Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Award type：Award from Japanese society, conference, symposium, etc.  Country：Japan

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1108/HFF-03-2019-0227

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Scopus

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DOI： 10.1016/j.ast.2019.105360

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Scopus

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DOI： 10.1063/1.5122260

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Scopus

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DOI： 10.1108/HFF-12-2018-0734

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Scopus

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DOI： 10.1108/HFF-03-2018-0094

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Scopus

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DOI： https://doi.org/10.1016/j.renene.2018.03.083

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

In this study, the smoothed profile-lattice Boltzmann method (SP-LBM) is proposed to determine the contact line dynamics on a hydrophobic or a hydrophilic curved wall. Two types of smoothed indicator functions are introduced, namely a function that identifies the solid domain for non-slip and non-penetration conditions and a function that denotes the boundary layer for no mass-flux and the wetting boundary conditions. In order to prevent fluid penetration into the solid boundary, the fluid-solid interaction force is computed based on the definition of the fluid velocity as proposed by Guo et al. [1]. In order to implement the Neumann boundary conditions for the order parameter and the chemical potential, the fluxes from the solid surfaces are distributed to relevant physical valuables through a smoothed profile. Several two-dimensional and three-dimensional numerical investigations including those determining the Couette flows, flow around a circular cylinder, transition layer on a wetting boundary, and dynamic behavior of a droplet on a flat or curved plate demonstrate the efficiency of the present method in calculating the contact angle of a droplet on curved surfaces with wall impermeability. The present model provides a simple algorithm to compute the surface normal vector and contact line dynamics on an arbitrarily shaped boundary by using a smoothed-profile. (C) 2017 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.compfluid.2017.09.012

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The particulate jet generated by solid particles falling from a circular orifice into an unbounded quiescent air is simulated. The three-dimensional vortex method, proposed for the analysis of particle-laden free turbulent flow in a prior study, is employed for the simulation. It is found that the falling particles induce complicated three-dimensional unsteady air flow involving large-scale eddies.
The air takes its maximum velocity at the jet centerline,
and the velocity profile satisfies the self-similarity around the centerline. The effect of particle diameter on the velocity distribution for the two phases is ivestigated. The entrained air flow rate is favorably compared with the value predicted by the analytical models.

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水流中に微小な気泡が分散し，水流と気泡が相互作用を及ぼし合いながら流れる気泡流に対する渦法を開発した．角柱周りの気泡流の解析に適用し，得られた結果が実験結果と一致することを確認し，解法の妥当性も示した．

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Solar Energy Society  

<p>A countermeasure against generator flooding was devised for a pico hydroelectric power generation system using a breastshot impulse turbine. Field tests showed that installing the generator at an angle so that its shaft side was lower prevented water from flooding the generator. In the indoor model experiments, there was no significant difference in turbine power characteristics when the inclination was less than 4 degrees.</p>

DOI： 10.24632/jsesc.2023.0_255

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Heliyon  

This study is focused on the development of a microhydraulic turbine that can stably and efficiently generate electricity even in channel where snow masses frequently flow down. A hydraulic turbine of an undershot cross-flow type was installed in an irrigation channel, and the change in the turbine performance was measured when spherical snowballs were released one by one from the upstream. The observation of the snowballs passing through the turbine was also conducted. Consequently, the variations in the power generated by the rotor were classified into three modes based on the motion of the snowballs, and could be organized by the ratio of the snowballs' cross-sectional area to the product of the rotor width and blade interval. Furthermore, the emergence of the power output overshoot phenomenon, in which the power output temporarily increases compared to clear water when the rotor restarts after stopping, was identified, and the relationship between the amount of loss when the rotor stops and that of electric energy gained during the overshoot was clarified. Certain guidelines for the installation of the undershot cross-flow type in irrigation channels of snowy regions was successfully obtained.

DOI： 10.1016/j.heliyon.2023.e20833

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Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Applications in Engineering Science  

In the field of metal cutting, the cutting oil scatters in air as a microscale oil mist, which adversely affects the work environment. A baffle plate-type mist trap was manufactured as simple equipment for collecting oil mist floating in air. The oil mist collection rate and pressure loss were determined using experiments and numerical simulations while varying the number of baffle plates and inflow velocity of air. The experimental results showed that the pressure drop increased with the number of baffle plates, whereas the oil mist collection rate improved. It was also clarified that larger particles can be collected as the number of baffle plates increased. Numerical simulations showed that a high amount of oil mist was trapped upstream of the second baffle plate, and the baffle plate placed further downstream had minimal contribution to oil mist collection. In both the experiments and numerical simulations, the oil mist collection efficiency was the highest when six baffle plates were arranged. This is because the pressure drop increases depending on the number of baffle plates, whereas the mist collection rate is almost constant when many baffle plates are placed.

DOI： 10.1016/j.apples.2023.100137

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Environment International  

A non-filter virus inactivation unit was developed that can control the irradiation dose of aerosolized viruses by controlling the lighting pattern of a 280 nm deep-UV (DUV)-LED and the air flowrate. In this study, the inactivation properties of aerosolized SARS-CoV-2 were quantitatively evaluated by controlling the irradiation dose to the virus inside the inactivation unit. The RNA concentration of SARS-CoV-2 remained constant when the total irradiation dose of DUV irradiation to the virus exceeded 16.5 mJ/cm2. This observation suggests that RNA damage may occur in regions below the detection threshold of RT-qPCR assay. However, when the total irradiation dose was less than 16.5 mJ/cm2, the RNA concentration monotonically increased with a decreasing LED irradiation dose. However, the nucleocapsid protein concentration of SARS-CoV-2 was not predominantly dependent on the LED irradiation dose. The plaque assay showed that 99.16% of the virus was inactivated at 8.1 mJ/cm2 of irradiation, and no virus was detected at 12.2 mJ/cm2 of irradiation, resulting in a 99.89% virus inactivation rate. Thus, an irradiation dose of 23% of the maximal irradiation capacity of the virus inactivation unit can activate more than 99% of SARS-CoV-2. These findings are expected to enhance versatility in various applications. The downsizing achieved in our study renders the technology apt for installation in narrow spaces, while the enhanced flowrates establish its viability for implementation in larger facilities.

DOI： 10.1016/j.envint.2023.108022

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Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Sensors  

The flowrate measurement of the gas–liquid two-phase flow frequently observed in industrial equipment, such as in heat exchangers and reactors, is critical to enable the precise monitoring and operation of the equipment. Furthermore, certain applications, such as oil and natural gas processing plants, require the accurate measurements of the flowrates of each phase simultaneously. This study presents a method that can simultaneously measure the volumetric flowrates of each phase of gas and liquid two-phase mixtures, Qg and Ql, respectively, without separating the phases. The method employs a turbine flowmeter and two pressure sensors connected to the pipes upstream and downstream of the turbine flowmeter. By measuring the rotational speed of the rotor and the pressure loss across the flowmeter, the flowrate of the two-phase mixtures Qtp = (Qg + Ql) and the gas volumetric flowrate ratio β = (Qg/Qtp) are determined. The values of Qg and Ql are calculated as βQtp and (1 − β)Qtp. This study also investigates the measurement accuracies for air–water two-phase flows at 0.67 × 10−3 ≤ Qtp ≤ 1.67 × 10−3 m3/s and β ≤ 0.1, concluding that the full-scale accuracies of Qtp, β, Qg, and Ql are 3.1%, 4.8%, 3.9%, and 3%, respectively. These accuracies either match or improve the accuracies of similar methods reported in the literature, indicating that the proposed method is a viable solution for the determination of phase-specific flowrates in gas–liquid two-phase mixtures.

DOI： 10.3390/s23094270

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PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Powder Technology  

In this study, the wake characteristics of a sphere with a uniaxial through-hole (that is, vented sphere) and that of a sphere without a through-hole (that is, basic sphere) are investigated to clarify the effect of the uniaxial through-hole on the vortex shedding in the wake. A sphere with a diameter of 25.4 mm having a 6 mm circular uniaxial through-hole was fixed to the test section of the wind tunnel and arranged perpendicularly to the streamwise direction. Results show that the vented sphere stabilizes the vortex shedding. A dominant peak at f=55Hz is observed in the wake of the vented sphere, whereas a convex peak over a wide range of 40<f<70Hz is observed in the wake of the basic sphere. In addition, the Reynolds stress in the wake of the vented sphere takes a constant value, whereas it attenuates as the flow moves toward the downstream direction for the basic sphere. The cause of these differences in the Reynolds stress is explained using the co-spectrum of the streamwise and spanwise velocity fluctuations. In the wake of the basic sphere, the negative co-spectrum peak over a wide range of 40<f<70Hz attenuates as the flow moves toward the downstream direction. In contrast, a clear negative peak appears in the wake of the vented sphere at f=55Hz, indicating the persistence of the periodic structure of the vortex shedding as the flow moves toward the downstream direction.

DOI： 10.1016/j.powtec.2022.118175

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ocean Engineering  

Water exit is an extremely important phenomenon because it contributes to the development of physics and biology and its application in engineering. In particular, it is necessary to consider the spatiotemporal change in the water mass entrained around an object to correctly understand the scenario of water mass. In this study, a solid particle is launched vertically upward in water toward the surface. The volume of the water mass is estimated using images captured from two orthogonal directions while considering the spatiotemporal development of the water mass. In this study, two water mass estimation methods (Models 1 and 2) are constructed and applied to experimental results of the water exit reported in a previous study by the authors Takamure and Uchiyama (2020a). Model 1 considers the spatiotemporal development of the water mass and estimates the vertical motion of the particle under the influence of water mass with high accuracy when the water mass barely develops around the particle (i.e., submergence depth is small). However, when a large water mass entrains around the particle with an increase in the submergence depth, the estimation accuracy of the volume of the water mass decreases owing to the multilayer structure of the water mass. Model 2 improves the estimation accuracy of the volume of the water mass when the particle covers a large amount of water mass by considering the existence of the multilayer structure of the water mass. For the largest submergence depth in the experiment in this study on the water exit of the particle, the estimation accuracy of the volume of the water mass for Model 1 was approximately 50%, while that for Model 2 was over 80%. Further, the motion of the particle can be estimated with high accuracy even if the water mass is relatively complex and has a multilayer structure by incorporating the effects of the multilayer structure of the water mass into Model 1. This method enables us to estimate the water mass quantity easily and accurately by photographing an object from two orthogonal directions using two synchronized high-speed cameras. This water mass estimation technique is useful for understanding physical phenomena and for engineering applications.

DOI： 10.1016/j.oceaneng.2022.112848

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Environment International  

A general-purpose virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The inside of the virus inactivation unit is a rectangular conduit with a sharp turn of 180° (sharp-turned rectangular conduit). Virus inactivation is attempted by directly irradiating the air passing through the conduit with DUV rays. The flow characteristics of air and virus particles inside the virus inactivation unit were investigated using numerical simulations. The air was locally accelerated at the sharp turn parts and flowed along the partition plate in the sharp-turned rectangular conduit. The aerosol particles moving in the sharp-turned rectangular conduit were greatly bent in orbit at the sharp turn parts, and then rapidly approached the partition plate at the lower part of the conduit. Consequently, many particles collided with the partition plates behind the sharp-turn parts. SARS-CoV-2 virus was nebulized in the virus inactivation unit, and the RNA concentration and virus inactivation rate with and without the emission of DUV-LEDs were measured in the experiment. The concentration of SARS-CoV-2 RNA was reduced to 60% through DUV-LED irradiation. In addition, SARS-CoV-2 passing through the virus inactivation unit was inactivated below the detection limit by the emission of DUV-LEDs. The virus inactivation rate and the value of the detection limit corresponded to 99.38% and 35.36 TCID50/mL, respectively.

DOI： 10.1016/j.envint.2022.107580

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Scopus

PubMed

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Renewable Energy  

This study developed a microhydraulic turbine that can stably and efficiently generate electricity even in canals where snow and ice masses frequently flow down. An undershot cross-flow hydraulic turbine was selected as the development target, and experiments were conducted in an irrigation canal in a heavy snowfall area. Spherical snowballs were made to flow down to the turbine from the upstream direction. The behavior of the snowballs and the power generation performance were investigated as these snowballs passed through the rotor. When the diameter of the snowball is smaller than the blade interval of the rotor, the snowball passing through the rotor causes a small decrease in power output. In contrast, when the diameter of the snowball is larger than the blade interval, the snowball is entrained between the rotor and canal bottom, temporarily stopping the rotor, and resulting in a large decrease in power generation. These results suggest that an undershot cross-flow hydraulic turbine can reduce power generation performance due to snow and ice masses when its blade interval is larger than the expected size of the snow and ice masses. This study developed some design guidelines for this turbine that are highly adaptable to snow- and ice-flowing irrigation canals.

DOI： 10.1016/j.renene.2022.09.062

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Advances  

Wake flows have significant effects on vehicles, buildings, and other objects encountered in daily life. Thus, wake control techniques are of practical importance and have been extensively investigated. One passive wake-control technique is to create a vent on a bluff body, which has been determined to be effective for wake control on a circular cylinder but has not been sufficiently studied for wake control on a sphere. Therefore, this study examined the effect of the vent angle on the characteristics of the wake of a sphere. A sphere with a uniaxial through-hole (vent) was placed in a uniform flow, and the vent angle was varied in the streamwise direction. The Strouhal number in the high-frequency and low-frequency modes was examined. The flow field in the sphere wake varied with respect to the vent angle. Three frequency modes (high, low, and very low), the occurrence of a switching phenomenon, wherein the velocity fluctuated between positive and negative values, and high-frequency energy injection by the vent were observed. In addition, a high dominant frequency was observed only in the positive velocity fluctuation region.

DOI： 10.1063/5.0098762

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1177/16878132221107249

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Advances  

A desktop-type air curtain system (DACS) capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the DACS. The aerosol blocking effect of the DACS was investigated using particle image velocimetry measurements. A scenario in which the arm of a patient in the blood collection room is placed on the gate of the DACS was also investigated. Air curtain flow was maintained inside the gate of the DACS. The aerosol particles approaching the DACS were observed to bend abruptly toward the suction port without passing through the gate, signifying that the aerosol particles were blocked by the air curtain flow. When the arm of the patient was placed on the gate of the DACS during blood collection, the airflow above the arm was disrupted. However, the aerosol blocking performance remained unaffected. We envisage that this system will be useful as an indirect barrier not only in the medical field but also in situations where sufficient physical distance cannot be maintained, such as at the reception counter.

DOI： 10.1063/5.0086659

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physics of Fluids  

In this study, the effect of Reynolds number (Re) on the mixing process of a two-layer density-stratified fluid, caused by the interaction between a vortex ring and the density interface, was numerically investigated using an improved vortex-in-cell method. The density-stratified fluid consisted of water (upper layer) and an aqueous sodium chloride solution (lower layer). Re of the simulated vortex ring was varied from 644 to 1932. We numerically investigated the behavior of the vortex ring and density-stratified fluid, and compared the same with that from a previously conducted experimental study from the literature. The vortex structure generated during the interaction was visualized in three dimensions. Furthermore, the mixing process was evaluated in terms of the stirring index, gradient of concentration, and stirring efficiency. The mixing behavior of the vortex ring was a function of the interaction pattern. For example, for a large Re, with the penetrative pattern, the stirring efficiency reached a constant value that was smaller than that from the partially penetrative pattern. The results showed that a strong stirring caused by an increase in Re of the vortex ring would not always lead to effective mixing.

DOI： 10.1063/5.0086096

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Association for Wind Engineering  

DOI： 10.5359/JWE.47.1

Scopus

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmefed.2022.os03-22

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>A virus inactivation unit that can inactivate viruses was developed using deep ultraviolet (DUV) LEDs that emit DUV rays with a wavelength of 280 nm. The flow characteristics of virus particles inside the virus inactivation unit were investigated using numerical simulations. The percentage of particles colliding on the inner wall of the virus inactivation unit is 56 %. Especially, many particles collide with the partition plates behind the sharp-turn parts.</p>

DOI： 10.1299/jsmemecj.2022.s055-11

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>A desktop-type air curtain device capable of being installed on a desk to protect healthcare workers from infectious diseases was developed. Pseudo-exhaled air containing aerosol particles emitted from a mannequin was blown toward the air curtain generated by the air curtain device. The aerosol blocking effect of the air curtain device was investigated using particle image velocimetry measurements. Air curtain flow was maintained inside the gate of the air curtain device. The aerosol particles approaching the air curtain device were observed to abruptly bend towards the suction port without passing through the gate, signifying that the aerosol particles were blocked by the air curtain flow.</p>

DOI： 10.1299/jsmemecj.2022.s055-10

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Powder Technology  

In this study, experiments and numerical simulations are performed where a hollow particle with a uniaxial through–hole is dropped freely in water, and its behavior is investigated. The distribution of falling particle trajectories reveals significant deviation in the direction perpendicular to the through–hole of the particle. In addition, the pressure distribution at the particle surface and the vorticity field of the wake of the particle are distributed asymmetrically in the plane perpendicular to the through–hole of the particle. Conversely, this pressure distribution and vorticity field are distributed symmetrically with respect to the direction parallel to the through–hole of the particle. Thus, this study clarifies that the movement of the particle in the direction parallel to the through–hole is suppressed. These results provide valuable novel insights into the control of particle motion.

DOI： 10.1016/j.powtec.2021.07.020

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Experimental Thermal and Fluid Science  

A spherical particle with a diameter of 25.4 mm and density of 2640 kg/m3 was launched vertically upward toward the free surface of calm water. The Froude number of the particle passing through the water surface was varied. The dependence of the Froude number on the particle motion and water surface behavior was investigated from the instant the particle crossed the water surface until it attained its maximum displacement position. Based on the classical energy conservation law, the energy lost in the interaction between the particle and water surface (i.e., interface containing energy, Eo) was estimated. Eo was found to increase with the increase in the Froude number when the particle crossed the water surface. In addition, owing to Eo at the maximum displacement position of the spherical particle, the height and width of the interfacial water sheet changed by the same ratio at the point of intersection of the upper side of the particle with the calm water surface. This result was in agreement with that obtained by changing the submergence depth, as reported by Takamure and Uchiyama (2020). This finding suggests that the characteristics of the interfacial water sheet are the dominant parameters influencing the interface containing energy. The presented findings can help determine the parameters to model the water exit problem.

DOI： 10.1016/j.expthermflusci.2021.110453

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Ocean Engineering  

An experiment was conducted in which a solid sphere with a density of 1,875 kg/m3 and diameter of 24.8 mm was launched vertically upwards in water towards the air–water interface. By changing the Reynolds number, Re, based on the launch velocity, the motion of the sphere due to interference with the air–water interface was investigated along with the behavior of the interface. The experimental results of the sphere's vertical position in water agree with the theoretical values. However, in air, the experimental results gave lower vertical positions than the theoretical values. When the Reynolds number where the sphere reaches the air–water interface is Rew1¯=0.2×103, the vertical trajectory of the sphere branches above and below the ensemble average immediately after passing the air–water interface. This difference in bifurcation does not depend on the Reynolds number in water. However, no branching occurs when Rew1¯ is large. There is an inverse relationship between the asymmetry of the air–water interface that occurs when the sphere passes through the interface and the sphere's maximum displacement. It was shown that the energy loss of the sphere and the asymmetry of the air–water interface have a linear relationship in all cases with different Reynolds numbers. This means that there is a invariant relationship between the energy lost by the sphere passing through the air–water interface and the asymmetry of the interface.

DOI： 10.1016/j.oceaneng.2021.109282

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Fluid Dynamics  

Abstract—: In this study, the interaction between a spherical solid particle descending in a fine-bubble plume and the fine-bubbles around the particle is investigated experimentally. The fine-bubbles, which are formed by water electrolysis and have an average diameter of 0.037 mm, rise via buoyancy to form bubble plumes. The average bubble velocity in the conduit is 0.05 mm/s. A spherical solid particle with a diameter of 11.1 mm and a density of 1130 kg/m3 is dropped into the fully-developed bubble plume. The particle falls in a meandering motion in the fine-bubble plume. In this process, the terminal velocity of the particles falling in the fine-bubble plume is almost identical to that of a particle falling in the quiescent water. Additionally, after the fine-bubbles have been separated from the particle surface, they flow into the wake of the particle, forming a stagnant region. The particle wake diameter increases threefold, as compared with its value in the downstream direction of the fine-bubble plume.

DOI： 10.1134/S001546282105013X

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Visualization  

Abstract: In this study, two vortex rings composed of upper fluid were continuously ejected vertically downward toward the interface of the two-layer density-stratified fluid. The motion of the vortex rings and behavior of the lower layer fluid were investigated via visualization experiment, and the effect of time interval between the injections of the two vortex rings on the mixing of the density-stratified fluid was investigated. The first emitted vortex ring (VRA) advected vertically downward in the upper layer, passed through the density interface, and then advected in the lower layer. After VRA reached the maximum depth in the lower layer, the upper part of the fluid mass ejected into the upper layer due to buoyancy. The lower fluid was entrained in the upper layer. Subsequently, a new vortex ring (VRC) was generated by the fluid mass ejected in the upper layer and advected vertically upward in the upper layer. The second vortex ring emitted (VRB) collided with the tip of the fluid mass of the VRA ejected from the lower layer. Subsequently, it slightly penetrated the lower layer, rolled up the lower layer fluid into the upper layer, and coalesced with VRC to collapse. In the process of vortex merging, the mixing of the upper and lower layers reached a maximum when the VRA reached the maximum depth. Furthermore, it was clarified that the mixing ability of the upper and lower layers depends on the ejection time interval of the two vortex rings. Graphic abstract: [Figure not available: see fulltext.]

DOI： 10.1007/s12650-020-00738-8

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Renewable and Sustainable Energy  

The volume penalization vortex-in-cell (VP-VIC) method, which combines the vortex-in-cell and vortex penalization methods, is a kind of immersed boundary method that has the advantage of accurately calculating the vorticity field near the boundary. It is expected to be used as a design tool for shape optimization. In this study, the flow and performance of a small Savonius turbine rotor (rotor diameter DR = 245 mm) with S-shaped blades, which is used for small-scale distributed power generation with output less than 100 kW, were analyzed by numerical simulation. The results were compared with those of previous experimental studies to examine the usefulness of the VP-VIC method for fluid analysis around the Savonius turbine. The Reynolds number (Re=U0DR/ν) based on the streamwise velocity U0 is 1.32×105. The volume penalization vortex-in-cell (VP-VIC) method is applied for flow simulation, and the rotational motion of the rotor is analyzed using the calculation method previously proposed by the authors for the fluid force acting on the solid boundary (blade surface). As a result, the relationship between the rotational speed of the rotor and the output coefficient obtained in this simulation is similar in the experimental results of Golecha et al. [Appl. Energy 88, 3027-3217 (2011)] using S-shaped blades. In particular, with an increase in the load torque, the rotational speed of the rotor decreases, and the rotor stops momentarily. When the rotor stops, the positive torque of clockwise rotation acts on the advancing blade, while the negative torque of counterclockwise rotation acting on the returning blade decreases; hence, the rotor restarts immediately after stopping. In addition, it is established that the rotor output can be accurately predicted. Based on the above, it is reconfirmed that the VP-VIC method is beneficial for predicting the performance of a Savonius turbine.

DOI： 10.1063/5.0051203

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Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Internet of Things (Netherlands)  

A self-powered wireless sensor node was developed to measure the water flowrate. It is composed of a turbine flowmeter and an IoT control unit. The turbine flowmeter generates electric power from the rotation of the rotor. The IoT control unit, consisting of a microcomputer and a low power wide area (LPWA) communication module, uses the power generated by the rotor rotation to detect the rotational speed of the rotor (the water flowrate) and to communicate wirelessly with a server on the Internet. Experiments were also conducted to evaluate the performance of the sensor node. The power generated by the rotor rotation was sufficient to operate the wireless sensor node as a self-powered unit. The full-scale accuracy and indication accuracy of the measured flowrate were 1.2% and 2.8%, respectively. The wireless sensor node could stably upload the measured flowrate to a server on the Internet.

DOI： 10.1016/j.iot.2020.100327

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Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Lecture Notes in Mechanical Engineering  

A solid sphere is launched vertically upward from water toward the air–water interface, and the modulation of the sphere’s motion and the behavior of the air–water interface induced by the sphere are investigated. Spheres with three different densities ρp are used: the almina sphere (ρp = 3900 kg/m3), teflon sphere (ρp = 2180 kg/m3), and duracon sphere (ρp = 1360 kg/m3). Through a visualization experiment on the motion of a sphere in water, it was demonstrated that the launch velocity of the sphere can be set with high accuracy. When the sphere passes through the air–water interface, it forms a complex interface while entraining water. Additionally, spheres with small ρp were demonstrated to not always vertically collide with the air–water interface; this causes different behaviors of the spheres in the air.

DOI： 10.1007/978-981-15-5183-3_17

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>A spool valve for water hydraulics, Aqua Drive System (ADS), which uses tap water, has some rectangular openings at control ports for precise control because of the low viscosity of the water. In the valve, cavitation happens quickly, and it occurs some troubles, e. g. noise and vibration, erosion, degradation of controllability. This study focuses on cavitation behavior and cavitation-related noise and pressure-flow rate characteristics of a rectangular orifice. Jet flow behavior issuing from a rectangular orifice strongly depends on its aspect ratio. So, cavitation could be affected by the aspect ratio. However, there is little knowledge of the relationships between the aspect ratio and cavitation noise or pressure-flow rate. This research investigates the aspect ratio influence on cavitation, noise, and pressure-flow rate characteristics with different pressure conditions. The equivalent diameter of the orifice used in this study is from 0.35 to 1.3mm, and it is based on a product spool valve model. As a result, the cavitation jet behavior changes with the orifice aspect ratio and the ambient pressure. But the noise characteristics show the almost same tendency for different aspect ratio.</p>

DOI： 10.1299/jsmehs.2021.58.f021

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study focused on the characteristics of a cavitating jet issuing from a small rectangular orifice with different aspect ratios. The orifice size is similar to the control port in a water hydraulic spool valve. The authors conducted the flow visualization to capture the overall and cross-sectional jet images. The maximum Reynolds number based on the equivalent diameter is approximately 1.3×10⁵. The results show that cavitation bubbles generate in the jet shear layer and just downstream the jet exit. The shape of the cavitation region varies with the streamwise position except for the two-dimensional orifice having an aspect ratio (AR) of 38.3. In the square orifice, the cavitation region rotates at 45 degrees from the jet exit like an axis switching. The cavitation region in the jet of AR=6.76 deforms from the rectangular shape. On the other hand, under the large aspect ratio condition, the shape of the cavitation region is maintained relatively downstream.</p>

DOI： 10.1299/jsmefed.2021.os03-20

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>A sphere with a uniaxial through-hole of 6mm with a sphere diameter of 25.4 mm and density of 1360 kg/m³ was launched vertically upward toward the free surface of calm water. The effect of initial angle of the uniaxial through-hole was investigated from the time the sphere passed through the calm water surface until it attained its maximum displacement position. When uniaxial through-hole of the sphere and the water surface are horizontal, a slight rotation occurs in the sphere that rises in the water. As the initial angle of the uniaxial through-hole increases, the sphere over the water surface deviates greatly from the central axis.</p>

DOI： 10.1299/jsmefed.2021.os03-04

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>In this study, we investigated the characteristics of the wake of a sphere with a uniaxial through-hole．The sphere diameter was 25.4 mm, and the through-hole diameter was 6 mm. The sphere was placed in a uniform flow so that the through-hole is perpendicular to the streamwise direction. The Reynolds number based on the sphere diameter and the uniform flow velocity was 12,000. The flow velocity was measured by a hot-wire anemometer. As a result, the velocity defect of the sphere was smaller than that of a sphere without such through-hole. However, the significant differences were hardly observed as the flow moves toward the downstream direction.</p>

DOI： 10.1299/jsmemecj.2021.s051-09

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>A self-powered wireless sensor node was developed to measure the water flowrate. It is composed of a turbine flowmeter and an IoT control unit. The IoT control unit, consisting of a microcomputer and a low power wide area communication module, uses the power generated by the rotor rotation to detect the rotational speed of the rotor (the water flowrate) and to communicate wirelessly with a server on the Internet. Experiments were also conducted to evaluate the performance of the sensor node. The power generated by the rotor rotation was sufficient to operate the wireless sensor node as a self-powered unit. The full-scale accuracy and indication accuracy of the measured flowrate were 1.2 % and 2.8 %, respectively. The wireless sensor node could stably upload the measured flowrate to a server on the Internet.</p>

DOI： 10.1299/jsmemecj.2021.s144-01

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>The purpose of this study is to improve the power generation efficiency of the self-powered turbine flowmeter developed by the authors. To increase the efficiency, the NACA airfoil was applied to the blade of the rotor. It was shown that the efficiency is favorably improved over the entire range of the flowrate by using the NACA airfoil blade.</p>

DOI： 10.1299/jsmefed.2021.os03-15

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physics of Fluids  

Submerged solid spheres with specific gravities relative to water ranging from 1.36 to 7.93 were launched vertically upward toward the free surface of calm water. The motion of each sphere and the behavior of the water surface were investigated from the time the sphere passed through the calm water surface until it attained its maximum displacement position. The energy lost in the interaction between the sphere and the water surface (i.e., the interfacial containing energy Eo) was estimated from energy conservation. A larger Eo at the maximum displacement position of the sphere led to a larger increase in the height and width of the interfacial water sheet where the upper side of the sphere intersected with the free surface of calm water. This result corresponded to the result obtained by changing the submergence depth, as reported by Takamure and Uchiyama ["Air-water interface dynamics and energy transition in air of a sphere passed vertically upward through the interface,"Exp. Therm. Fluid Sci. 118, 110167 (2020)]. This aspect suggests that the characteristics of the interfacial water sheet are the dominant parameters influencing Eo. The presented findings can facilitate the determination of parameters to model the water exit problem.

DOI： 10.1063/5.0024032

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.powtec.2020.05.091

Web of Science

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>The characteristics of a fine-bubble plume passing through two tandem cylinders are investigated. Fine-bubbles with a mean diameter of 0.055 mm are released by water electrolysis from electrodes placed at the bottom of a tank. They induce an upward water flow around them with rising due to buoyancy. Orthogonally to the axis of such fine–bubble plume, two cylinders with a diameter <i>D</i> of 30 mm are arranged in tandem. The distance between the cylinders, <i>L</i>, ranges between 1.5<i>D</i> and 3<i>D</i>. This study visualizes the bubbles and water flow around the cylinders. It also measures the bubble velocity distribution. The experiments reveal the water and bubble shear layers originating at the sides of the lower cylinder and make clear their behavior around the upper cylinder. This study elucidates the effects of <i>L</i> on the characteristics of the fine-bubble plume, such as the stagnant bubbly flow and the bubbly wake around the cylinders.</p>

DOI： 10.1299/JFST.2020JFST0019

Scopus

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>The flow and performance of a rotor of a Savonius hydraulic turbine provided with a shield plate were analyzed by the two-dimensional simulations. The rotor diameter <i>D_R</i> is 142 mm, and the Reynolds number based on the velocity of the main flow <i>U</i>₀, <i>U</i>₀<i>D_R</i>/<i>ν</i>, is 1.1×10⁵. The shield plate with a length of 0.5<i>D_R</i> is installed upstream of the rotor, perpendicular to the main flow. The comparative experimental studies have visualized the flow and clarified that the shield plate increases the power output of the rotor. The vortex in cell method combined with the volume penalization method was applied to the flow simulation, and the torque acting on the rotor was computed with a custom method by the authors. The simulated flows around the shield plate and rotor agreed with the experimentally visualized ones. The simulation successfully revealed the effect of the shield plate on the flow and power output of the rotor. These demonstrate the applicability of the present simulation method for the performance prediction of the rotor of Savonius hydraulic turbines provided with a shield plate.</p>

DOI： 10.1299/transjsme.20-00181

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmefed.2020.os03-10

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmemecj.2020.s05129

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>In a present experiment, a solid sphere with a density of 2600 kg/m³ and diameter of 25.4 mm was launched vertically upward in water toward the air-water interface. The submergence depth was changed and the launch velocity was adjusted so that the Reynolds number of the sphere immediately after passing the air-water interface was almost equal at each submergence depth. The energy ratio <i>E_p</i>/<i>E_k</i> was defined as the ratio of the kinetic energy <i>E_k</i> of the sphere immediately after it passed through the air-water interface to the potential energy <i>E_p</i> when the sphere reached the maximum displacement position. <i>E_p</i>/<i>E_k</i> decreased when the submergence depth was <i>H</i>/<i>d</i> < 3. However, it had a constant value of <i>E_p</i>/<i>E_k</i> ~ 0.57 when the submergence depth was <i>H</i>/<i>d</i> ≥ 3. In addition, when the submergence depth was <i>H</i>/<i>d</i> ≥ 3, the ratio of each energy became similar immediately after passing through the water surface. This indicated that each energy distribution had reached the equilibrium state.</p>

DOI： 10.1299/jsmemecj.2020.s05110

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmetokai.2020.69.602

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019  

This study experimentally investigates the mixing of a two-layer density-stratified fluid of water (upper layer) and aqueous sodium chloride (NaCl) solution (lower layer) induced by the interaction between a vortex ring and the density interface. The vortex ring, which consists of water, is launched from an orifice in the upper layer toward the density interface, after which its motion, along with the behavior of the lower fluid, is visualized through a planar laser-induced fluorescence method. The Atwood number that expresses the nondimensional density jump across the density interface is set at 0.0055, and the Reynolds number Re of the vortex ring is varied from 2050 to 3070. The visualization experiment clarifies that the vortex ring penetrating the density interface is bounced while collapsing in the lower fluid. Furthermore, it elucidates that the bounced upper fluid entrains the lower fluid into the upper layer by inducing a second vortex ring consisting of the lower fluid. Thus, this study reveals the effect of Re on the mixing of the upper and lower fluid induced by the launched vortex ring.

DOI： 10.1115/AJKFluids2019-4972

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>Cavitation is one of the significant issues for water hydraulic components. This study focuses on the relationships between the cavitation phenomenon and noise under various pressure condition. Cavitating jet from a rectangular orifice with different aspect ratio was investigated in this study to reveal the critical parameter for the cavitation in a water hydraulic spool valve. The author performed flow visualization and noise measurement. The experimental results showed that the relationship between jet behavior and noise characteristics. The noises of all aspect ratio jets had a peak at the same positive downstream pressure. The both of cavitation and noise were suppressed for the largest aspect ratio of <i>AR</i>=52.0.</p>

DOI： 10.1299/jsmefed.2019.os3-23

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>To investigate the variation in a sphere's motion and the behavior of the air-water interface induced by the sphere, a solid sphere is launched vertically upward in water toward the air-water interface. Four spheres with different densities <i>ρ_p</i> were studied: a stainless steel sphere (<i>ρ_p</i> = 7930 kg/m³), an alumina sphere (<i>ρ_p</i> = 3900 kg/m³), a Teflon sphere (<i>ρ_p</i> = 2180 kg/m³), and a Duracon sphere (<i>ρ_p</i> = 1360 kg/m³). By experimentally visualizing the sphere motion in water, their launch velocity can be set with high accuracy. When a sphere passes through the air--water interface, it makes the interface more complex and entrains water. Additionally, spheres with a small value of <i>ρ_p</i> were demonstrated to not always vertically collide with the air--water interface.</p>

DOI： 10.1299/jsmefed.2019.os3-08

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This article describes the flow around bluff body in microbubble plume. Firstly, the flow around two circular cylinders arranged in tandem within a microbubble plume was investigated. The experiment revealed the water and bubble shear layers originating at the sides of the lower cylinder, and allowed the elucidation of their behavior around the upper cylinder. Secondly, the motion of a solid spherical particle in a microbubble plume and the behavior of bubbles around the particle were studied. The studies clarified the bubble distribution and velocity around the particle.</p>

DOI： 10.1299/jsmemecj.2019.w05102

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study investigates the flow past two cylinders arranged in tandem within a microbubble plume inside a tank. Microbubbles with a mean diameter of 0.055 mm are released by water electrolysis from electrodes placed at the bottom of the tank. Upon rising, these microbubbles induce an upward water flow around them due to buoyancy. Orthogonally to the axis of this microbubble plume, two cylinders with a diameter <i>D</i> of 30 mm are arranged in tandem. The distance between the cylinders, <i>L</i>, ranges between 1.5<i>D</i> and 3<i>D</i>. The bubbles and the water flow around the cylinders are visualized, and the bubble velocity distribution is measured. The experiments reveal the water and bubble shear layers originating at the sides of the lower cylinder, and allow the elucidation of their behavior around the upper cylinder. Furthermore, this study makes clear the effects of <i>L</i> on the flow around the two cylinders, such as the stagnant bubbly flow and the bubbly wake.</p>

DOI： 10.1299/jsmefed.2019.os3-07

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study is concerned with the numerical simulations of the flow and performance of a rotor of a hydraulic Savonius turbine. The flow was simulated using the vortex in cell (VIC) method in combination with the volume penalization (VP) method. The torque acting on the rotor was computed using a custom method, which can accurately calculate the fluid forces on solid bodies in flows simulated by the VIC-VP method, to analyze the rotational speed and power output of the rotor. The simulated flow around the rotating blades agreed qualitatively with the experimentally visualized flow, and the analyzed relation between the rotor's rotational speed and power output agreed well with the experimentally measured relation. These demonstrate that the VIC-VP method in combined with the authors' method for calculating fluid forces is applicable for the simulations of flow and performance of hydraulic Savonius turbines.</p>

DOI： 10.1299/jsmemecj.2019.s05121

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>Pin-on-disk sliding tests have been carried out to investigate lubrication properties of nanometer-thick liquid films. However, it is difficult to experimentally observe the detailed flow behavior of the films at the nanoscale contacting interface. To solve this problem, we performed numerical simulations with the moving particle semi-implicit (MPS) method in this study. To model a pin sitting on a rotating disk lubricated with a nanometer-thick liquid film, the effects of surface tension and external force were taken into account in the governing equation. As a result, details of the behavior of the film and pin and their interference were visualized. This result suggests that the MPS method is potentially useful for clarifying the mechanism of lubrication with nanometer-thick liquid films.</p>

DOI： 10.1299/jsmemecj.2019.s16105p

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019  

This study investigates the flow past two cylinders arranged in tandem within a microbubble plume inside a tank. Microbubbles with a mean diameter of 0.055 mm are released by water electrolysis from electrodes placed at the bottom of the tank. Upon rising, these microbubbles induce an upward water flow around them due to buoyancy. Orthogonally to the axis of this microbubble plume, two cylinders with a diameter D of 30 mm are arranged in tandem. The distance between the cylinders, L, ranges between 1.5D and 3D. The bubbles and the water flow around the cylinders are visualized, and the bubble velocity distribution is measured. The experiments reveal the water and bubble shear layers originating at the sides of the lower cylinder, and allow the elucidation of their behavior around the upper cylinder. Furthermore, this study makes clear the effects of L on the flow around the two cylinders, such as the stagnant bubbly flow and the bubbly wake.

DOI： 10.1115/AJKFluids2019-4971

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This article describes the flow around bluff body in microbubble plume. Firstly, the flow around two circular cylinders arranged in tandem within a microbubble plume was investigated. The experiment revealed the water and bubble shear layers originating at the sides of the lower cylinder, and allowed the elucidation of their behavior around the upper cylinder. Secondly, the motion of a solid spherical particle in a microbubble plume and the behavior of bubbles around the particle were studied. The studies clarified the bubble distribution and velocity around the particle.</p>

DOI： 10.1299/jsmemecj.2019.w15102

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier Ltd  

This study develops a micro-hydraulic turbine with excellent performance in the passage of foreign matter included in the water flow. The runner has four blades, with a circular hollow around the rotating axis to pass foreign matter through the runner. The ratio of the hollow diameter D2 to the runner outer diameter D1, D2/D1, is defined as the hollow ratio ε. Laboratory experiments are conducted by introducing polyester fibers into the water flow as foreign matter. The turbine efficiency η decreases with increasing ε under the fiber-free condition. For the runner having no hollow (ε = 0), η decreases drastically with increasing the mass of the introduced fibers. This is due to the blockage of the runner by the fibers. But η for the runners provided with the hollow decreases less. This demonstrates that the hollow makes the fibers pass successfully through the runner. Additional experiments are conducted using the runner with ε = 0.25. The blade leading edges near the central axis are rounded with radius R. When R/D1 = 0.1875, the decrease in η due to the fibers is extremely small. The rounded leading edges successfully prevent the runner from catching the fibers, demonstrating that they effectively heighten the passage performance of foreign matter through the runner.

DOI： 10.1016/j.renene.2018.03.083

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1177/1748301818771811

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Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study conducts experimental exploration on the motion of a solid spherical particle falling in a microbubble plume and the bubble behavior around the particle. Bubbles with a mean diameter of 0.037 mm, released into a rectangular conduit using the electrolysis of water, rise by the buoyant force and induce a bubble plume. A spherical particle with a diameter 11.1 mm and density 1130 kg/m³ is released from the top of the conduit. The experiment clarifies that the particle falls meandering through the plume and that the terminal velocity is almost the same as that for a particle falling in quiescent water. The experiment also makes clear that the bubbles separate from the particle surface and that the separation induces a stagnation area just behind the particle. A wake still exists at a location with a distance of three times of the particle diameter from the particle.</p>

DOI： 10.1299/jsmefed.2018.os5-20

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study investigates the motion of a spherical particle in microbubble plume and the bubble behavior around the particle. Microbubbles with a mean diameter of 0.037 mm, released into a rectangular conduit using the electrolysis of water, rise by the buoyant force and induce a bubble plume in the conduit. A spherical particle with a diameter 10 mm and a density 1022 kg/m³ is placed on a mesh stretched near the bottom of the conduit at the commencement of the microbubble release from the cathode. The experiments clarify the effects of the bubble volumetric flux on the motion of the particle. They also explore the bubble distribution and velocity around the rising, still and lowering particle to make clear the front stagnation and wake of the particle.</p>

DOI： 10.1299/jsmemecj.2018.s0510401

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>In the present study, we propose a method for calculating the fluid dynamic forces acting on bodies in a two-dimensional simulation of a flow around a moving body by using the vortex–in–cell method. The body is represented using the volume penalization method which introduces the influence of the body on the flow as an external force in the form of a penalization term into the Navier–Stokes equation. The pressure field is computed by solving the Poisson equation, which is derived by obtaining the divergence of the Navier-Stokes equation. The pressure and viscous stress on the body surface are obtained from a quadratic function along the vector normal to the surface. A flow around a circular cylinder oscillating in still water is simulated, and the fluid dynamic force acting on the cylinder is calculated using the proposed method. The velocity profiles across four cross-sections at three different time points agree well with the results of a measurement conducted using a laser Doppler velocimeter. The in-line force acting on the cylinder agrees with the results of the simulations performed using the boundary-conforming formulation.</p>

DOI： 10.1299/jsmemecj.2018.s0510105

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study simulates the behavior of a vortex ring launched toward the interface of a two-layer density stratified fluid and the resulting mixing phenomena between the fluids. Initially, the density-stratified fluid is in a static condition in a tank. The upper and lower fluids are glycerol aqueous solution and an aqueous solution of potassium dihydrogen phosphate, respectively. The vortex ring with a diameter of 26.4 mm is launched vertically downward from the upper fluid region. It travels by the vertical motion toward the density interface. The Reynolds number, based on the circulation of the vortex ring, is 3500. The simulation conditions are parallel with an experimental work of one of the authors. The vortex in cell method, which was presented by the authors for flow simulations of two-layer density stratified fluid in a prior study, is used. The simulation favorably highlights the collision, deformation and penetration of the vortex ring at the density interface. It also successfully reveals the mixing between the upper and lower fluids induced by the motion of the vortex ring. These simulated results are discussed by comparing with the corresponding experimental ones.</p>

DOI： 10.1299/jsmemecj.2017.s0520406

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>This study numerically investigates the mixing of a two-layer density stratified fluid caused by vortex rings. Initially, the density-stratified fluid is in a static condition in a tank. The upper and lower fluids are glycerol aqueous solution and an aqueous solution of potassium dihydrogen phosphate, respectively. Two vortex rings are arranged on a vertical line in the lower fluid, and the axial interval is 80 mm. The diameter of the vortex ring is 26.4 mm, and the Reynolds numbers based on the circulation are 4000, 6000, and 8000. The vortex rings are launched simultaneously in the vertically upward direction. The simulation explores the collision of the vortex rings with the density interface, the entrainment of the fluids into the vortex rings, and the resulting mixing between the fluids. It also clarifies the behavior of each vortex ring, such as the deformation and the interaction with the density interface.</p>

DOI： 10.1299/jsmemecj.2017.s0520405

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Hosokawa Powder Technology Foundation  

<p>The generation and transport of solid particle clusters by a vortex ring launched into quiescent water are explored. A vortex ring launcher, composed of a cylinder and a piston, is mounted at the bottom of a water tank. Polyacetal particles are placed on a mesh stretched near the cylinder outlet. The number of particles is 100, the mean diameter and density are 1.52 mm and 1417 kg/m³ respectively. The water in the cylinder is discharged vertically upward into the tank by the piston to launch the particle-laden vortex ring. Such two-phase flows of the Reynolds number Re based on the piston velocity and the cylinder diameter at 6500, 7500 and 13000 are investigated. The particles are entrained just after the launch of the vortex ring of <i>Re</i> = 7500 and 13000. The resultant particle cluster is transported by the convection of the vortex ring. The water velocity on the vertical cross-section of the vortex ring lessens due to the particles, resulting in the reduction of the circulation of the vortex ring. The reduction is larger for the lower <i>Re</i>.</p>

DOI： 10.14356/hptf.15102

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Engineering  

This study is concerned with the feasibility of power generation using a pico-hydraulic turbine from sewage flowing in pipes. First, the sewage flow rate at two connection points to the Toyogawa River-Basin Sewerage, Japan, was explored for over a year to elucidate the hydraulic energy potential of the sewage. Second, the performance of the pico-hydraulic turbine was investigated via laboratory experiments that supposed the turbine to be installed in the sewage pipe at the connection points. This study indicates that the connection points have hydraulic potential that can be used for power generation throughout the year. It also demonstrates that the pico-hydraulic turbine can be usefully employed for power generation from sewage flowing in the pipe at the connection points.

DOI： 10.1016/J.ENG.2016.04.007

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Powder Technology  

The interactions between a vortex ring and solid particles near a horizontal wall in the air are explored in this study using numerical simulations. The vortex ring is moved toward the particles initially arranged in layers above the wall. The Reynolds number of the vortex ring is 1146. When the Stokes number St is 0.1, the particles initially arranged around the central axis of the vortex ring are driven toward the wall while moving in the radial direction. They distribute circularly along the outer edge of the particle cluster on the wall. The particles near the layer's edge are whirled up. Three-dimensional vortex structures, including secondary and tertiary vortex rings, are produced around the particles. When St = 1, vortical flows induced around the particles appear in the broader region. They reduce rapidly owing to the motion of particles relative to the wall (collision and rebound). The drag force acting on the particles lowers the strength of the vortex ring and also suppresses the approach of the vortex ring toward the wall.

DOI： 10.1016/j.powtec.2016.07.042

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Advances and Applications in Fluid Mechanics  

This study is concerned with the numerical simulation of incompressible flows around two circular cylinders in tandem arrangement. A vortex in cell (VIC) method combined with an immersed boundary (IB) method is applied to the simulation. The Reynolds number Re, based on the diameter D of cylinder and the flow velocity upstream of the front cylinder, ranges from 200 to 9500. The distance L between the cylinders is varied from 1.5D to 8D. The simulated flow characteristics, such as the behavior of the shear layers separated from the cylinders, the vortex shedding and the fluid forces acting on the cylinders, are favorably compared with the existing results. The simulation can also successfully analyze the effects of Re and L on the flow characteristics. These simulation results demonstrate that the VIC method combined with the IB method is usefully applicable to the simulation of incompressible flows around two tandem cylinders.

DOI： 10.17654/FM019040787

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Chemical Engineering Science  

The interactions between rising air bubbles and the vortex core of swirling water flows in a cylindrical tank are experimentally investigated. A stirring disc mounted at the center of the tank bottom is rotated to produce swirling water flows around the central (vertical) axis of the tank, and small air bubbles are successively released from tubules mounted near the stirring disc. The bubbles rise helically in the swirling water flow because of the buoyancy force, and some bubbles are entrained into the vortex core. The precessional amplitude of the vortex core is enhanced by the bubbles when the bubble flow rate Qg is very low. But it decreases with increasing Qg when Qg is larger than a certain value. In the horizontal cross-sections near the stirring disc, the bubbles make the water flow field nonaxisymmetric and reduce the water velocity. The water velocity variation due to the bubbles affects the shape of the vortex funnel formed at the water surface.

DOI： 10.1016/j.ces.2015.11.042

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>Mixing phenomena, induced by a jet issued diagonally upward into a two-layer densitystratified fluid in a cylindrical tank, are numerically simulated. The upper and lower fluids are water and a NaCl aqueous solution, respectively. The mass concentration of the NaCl-water solution is 0.02. The lower fluid is issued from a nozzle mounted on the tank bottom. The angle of the nozzle to the tank bottom is 60 degree, and the Reynolds number defined by the jet velocity and the nozzle diameter ranges from 475 to 3089. The simulation highlights the jet behavior relative to the density interface and the resultant mixing phenomena.</p>

DOI： 10.1299/jsmefed.2016.0207

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Web of Science

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

DOI： 10.1299/jsmecmd.2016.29.050

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>The interactions between rising air bubbles and the vortex core of swirling water flows in a cylindrical tank are experimentally investigated. A stirring disc mounted at the center of the tank bottom is rotated to produce swirling water flows around the central (vertical) axis of the tank, and small air bubbles are successively released from tubules mounted near the stirring disc. The bubbles rise helically in the swirling water flow because of the buoyancy force, and some bubbles are entrained into the vortex core. The precessional amplitude of the vortex core is enhanced by the bubbles when the bubble flow rate <i>Q</i>_g is very low. But it decreases with increasing <i>Q</i>_g when <i>Q</i>_g is larger than a certain value. In the horizontal cross-sections near the stirring disc, the bubbles make the water flow field non- axisymmetric and reduce the water velocity.</p>

DOI： 10.1299/jsmemecj.2016.s0520304

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

<p>We improve the accuracy and the numerical stability of the immersed boundary-lattice Boltzmann method (IB-LBM) to calculate the motion of a droplet on hydrophobic surfaces in complex geometry. To exactly derive the Chan-Hilliard equation, we use the proper source term proposed by Liang and the two-relaxation-time (TRT) collision operator. The series of the numerical tests, including Zalesak’s disk rotation, a single vortex, and a deformation of a sphere demonstrate that the computational effectiveness of the TRT collision operator is superior to that of the multi relaxation time collision operator. Analytical and numerical solutions of the symmetric shear flows demonstrate that the implicit diffuse direct-forcing method without the computational cost of the sparse matrix solver reduces the velocity slip and boundary value deviation as effectively as the implicit correction method for any relaxation times. The present IB-LBM with the TRT collision operator appropriately calculates the contact angle of liquids on the arbitrary shaped surfaces.</p>

DOI： 10.1299/jsmefed.2016.0711

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy  

This study simulates the flow through a small-scale open cross-flow hydraulic turbine and analyzes the turbine's performance. The simulation employs a two-dimensional particle method that was used for the simulation of a small-scale impulse-type hydraulic turbine in a prior study. Flow in the turbine is successfully simulated, with the simulated turbine performance showing good agreement with experimental measurements. The simulations also clarify that the deterioration in performance with increasing water flow rate is caused by the degeneration of the radially outward flow between the rotor blades.

DOI： 10.1177/0957650915592260

Web of Science

Scopus

Language：English   Publishing type：Research paper (scientific journal)   Publisher：International Journal of Turbo and Jet Engines  

The aim of this study was to develop a nano-hydraulic turbine utilizing drop structure in irrigation channels or industrial waterways. This study was focused on an open-type cross-flow turbine without any attached equipment for cost reduction and easy maintenance. In this study, the authors used an artificial indoor waterfall as lab model. Test runner which is a simple structure of 20 circular arc-shaped blades sandwiched by two circular plates was used The optimum inlet blade angle and the relationship between the power performance and the flow rate approaching theoretically and experimentally were investigated. As a result, the optimum inlet blade angle due to the flow rate was changed. Additionally, allocation rate of power output in 1st stage and 2nd stage is changed by the blade inlet angle.

DOI： 10.1515/tjj-2015-0005

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This study is concerned with the numerical simulation of the jet issued into two-layer density-stratified fluid in a cylindrical tank. Vortex in cell (VIC) method combined with an Immersed Boundary (IB) method is applied to the simulation. The upper and lower fluids are water and a NaCl-water solution, respectively, and the lower fluid is issued vertically upward from a nozzle on the bottom of the tank. The Reynolds number Re defined by the jet velocity and the nozzle diameter ranges from 95 to 1188, and the mass concentration of the NaCl-water solution is set at 0.02. The simulation highlights that the jet behavior relative to the density interface and the resultant mixing phenomena depend on Re. Such simulated results are confirmed to agree well with the experimentally visualized ones, demonstrating the validity of the present simulation method.

DOI： 10.1299/jsmefed.2015._0210-1_

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This study explores the bubble plume around a circular cylinder in a water tank. Small gas bubbles with diameter of less than 0.06 mm are released from electrodes on the bottom of the tank by using the electrolysis of water. They induce the water flow with rising by the buoyant force. In such bubble plume, a circular cylinder with diameter D of 30 mm is mounted at an elevation of 6.5D above the electrodes. This study visualizes the bubbles and water flow around the cylinder and measures the bubble velocity distribution. The experiment elucidates the separated shear layers originating from the cylinder wall, their roll-up, and the bubble entrainment in the resultant large-scale eddies behind the cylinder.

DOI： 10.1299/jsmemecj.2015._s0510402-

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)  

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Advances and Applications in Fluid Mechanics  

This study proposes a numerical simulation method for a jet flow issued into a two-layer density-stratified fluid. The method is based on the Vortex in Cell method, which discretizes the vorticity field into vortex elements and computes the time evolution of the flow by tracing the convection of each vortex element using the Lagrangian approach. The proposed method is applied to simulate a jet flow, which was experimentally investigated in the authors’ prior study, so as to demonstrate the validity of the method. The simulation highlights that the jet behavior relative to the density interface depends on the jet Reynolds number and that it agrees well with the experimentally visualized one.

DOI： 10.17654/15-aafm-01701-115

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Procedia IUTAM  

A vortex in cell (VIC) method for bubbly flow is proposed. It computes the time evolution of the flow by calculating the behavior of the vortex element as well as the bubble motion with the Lagrangian approach. The proposed method is also applied to simulate a bubble plume to demonstrate the validity. In a tank containing water, small air bubbles are released from the base of the tank. The bubbles rise due to the buoyant force, inducing the water flow around them. The simulation for the plume at the starting period highlights that the rising bubbles induce vortex rings at their top and that a bubble cluster appears owing to the entrainment of the bubbles into the vortex rings. The rising velocity for the top of the bubbles is proportional to the square root for the flow rate of the released bubbles, being consistent with an existing theoretical investigation. The simulation also demonstrates that the developed bubble plume having jet characteristics is successfully captured.

DOI： 10.1016/j.piutam.2015.11.014

Web of Science

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Advances and Applications in Fluid Mechanics  

A simulation method for gas-liquid bubbly flows entraining small bubbles is proposed. It is based on the Vortex in Cell (VIC) method originally presented to simulate incompressible single-phase flows. The staggered grid discretization method and the vorticity correction method, which were proposed for the VIC method simulating single-phase flows by the authors’ prior study, are employed. The liquid velocity field is discretized with vortex elements, and the time evolution of the bubbly flow is simulated by calculating the behavior of each vortex element and the bubble motion through the Lagrangian approach. The proposed method is applied to the simulation of a bubble plume in a water tank to discuss the validity and applicability. Small air bubbles are released successively from the base of the tank, and their rise due to the buoyant force induces the water flow around them. The simulation at the starting period of the bubble release highlights that the rising bubbles induce vortex rings at their top and that a bubble cluster appears owing to the entrainment of the bubbles into the vortex rings. The rising velocity of the top of the bubbles is proportional to the square-root of the flowrate of the released bubbles, being consistent with the existing theoretical and numerical investigations. The simulation also demonstrates that the developed bubble plume having jet characteristics is successfully captured.

DOI： 10.17654/15-aafm-01701-091

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ICOPE 2015 - International Conference on Power Engineering  

This study is concerned with the development of a hollow micro-hydraulic turbine excellent in foreign matter passage performance. The runner has a circular hollow around the central (rotating) axis so that foreign matter included in water can easily flow without blocking the turbine. The laboratory experiments are conducted to investigate the turbine performance. The guide vane successfully heightens the turbine efficiency. Though the maximum efficiency decreases with increasing the hollow ratio ϵ when ϵ>0.25, it remains unchanged when ϵ≤ 0.25. The hollow of the runner effectively heightens the passage performance of the polyester fibers entrained into the turbine. When employing the guide vane, the developed micro-hydraulic turbine of ϵ≥0.375 is not blocked by the fibers and maintains its function.

Scopus

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This study is concerned with the development of a hollow micro-hydraulic turbine excellent in foreign matter passage performance. The runner has a circular hollow around the central (rotating) axis so that foreign matter included in water can easily flow without blocking the turbine. The laboratory experiments are conducted to investigate the turbine performance. Though the turbine efficiency decreases with increasing the hollow ratio e when ε>0.25, it remains unchanged when ε&le;0.25. The hollow of the runner effectively heightens the passage performance of the polyester fibers entrained into the turbine. The developed micro-hydraulic turbine of ε&ge;0.375 is not blocked by the fibers and maintains its function.

DOI： 10.1299/jsmeenv.2015.25.143

CiNii Research

Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of Mechanical Engineers  

This study is concerned with the development of a hollow micro-hydraulic turbine excellent in foreign matter passage performance. The runner has a circular hollow around the central (rotating) axis so that foreign matter included in water can easily flow without blocking the turbine. The laboratory experiments are conducted to investigate the turbine performance. The guide vane successfully heightens the turbine efficiency. Though the maximum efficiency decreases with increasing the hollow ratio ε when ε>0.25, it remains unchanged when ε≦0.25. The hollow of the runner effectively heightens the passage performance of the polyester fibers entrained into the turbine. When employing the guide vane, the developed micro-hydraulic turbine of ε≧0.375 is not blocked by the fibers and maintains its function.

DOI： 10.1299/jsmeicope.2015.12._icope-15-_70

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：ASME/JSME/KSME 2015 Joint Fluids Engineering Conference, AJKFluids 2015  

Jet flow issued into two-layer density-stratified fluid in a cylindrical tank is numerically simulated. Vortex in cell (VIC) method combined with an Immersed Boundary (IB) method, which is presented by the current authors, is applied to the simulation. The upper and lower fluids are water and a NaCl-water solution, respectively, and the lower fluid is issued vertically upward from a nozzle on the bottom of the tank. The Reynolds number Re defined by the jet velocity and the nozzle diameter ranges from 95 to 1188, and the mass concentration of the NaCl-water solution Co is set at 0 and 0.02. The simulation highlights that the jet behavior relative to the density interface and the resultant mixing phenomena depend on Re. Such simulated results are confirmed to agree well with the experimentally visualized ones, demonstrating the validity of the present simulation method.

DOI： 10.1115/ajkfluids2015-24394

Scopus

Authorship：Lead author   Language：English  

Language：English  

Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (invited, special)  

Language：English   Presentation type：Oral presentation (invited, special)  

Applicant：国立大学法人名古屋大学

Application no：2018-129481  Date applied：2018.7

Applicant：名古屋大学

Application no：2017-043135  Date applied：2017.3