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Air-water interface dynamics and energy transition in air of a sphere passed vertically upward through the interface

Takamure, K; Uchiyama, T

EXPERIMENTAL THERMAL AND FLUID SCIENCE 118 巻 2020年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Experimental Thermal and Fluid Science

The water exit problem is a fundamental problem in fluid dynamics, and the behavior of the air–water interface and the energy transition of an object exiting water have not been thoroughly investigated. In this study, a solid sphere with a density of 2.64×103kg/m3 and diameter of d=25.4 mm was launched vertically upward in water toward the air–water interface. The motion of the sphere and the behavior of the interface were investigated for varying submergence depths H from the launch position of the sphere to the interface. The launch velocity was set so that the Reynolds number immediately after the sphere passed the air–water interface was about 3000 for all cases of H. The kinetic and potential energies of the sphere and the energy lost because of the air–water interface (i.e., interfacial containing energy) were estimated based on the classical law of energy conservation. For H/d⩽3, the ratio between the kinetic energy immediately after passing through the air–water interface and the potential energy at the maximum displacement position decreases with increasing H, but this energy ratio takes a constant value of 0.57 for H/d⩾4. Additionally, for H/d⩾4, kinetic energy is transformed to potential energy and interfacial containing energy at a fixed ratio for each vertical position. The spreading characteristics of the water mass after the sphere has passed the air–water interface and the thickness and width of the interfacial water sheet when the top of the sphere reached the calm free surface were investigated by focusing on their relationship to the energy distribution. For H/d⩾4, where the energy ratio takes a constant value, the increase in the rate of spread of the water mass with increasing H/d is clearly smaller than that of H/d⩽4. Furthermore, for H/d⩾4, the ratio between the thickness and width of the interfacial water sheet is constant. In other words, in the region where the ratio between the kinetic energy of the sphere immediately after passing through the air–water interface and the potential energy at the maximum displacement position has a constant value, the shape of the interfacial water sheet is self-similar. These findings contribute to the determination of variable parameters when modeling the water exit problem.

DOI： 10.1016/j.expthermflusci.2020.110167

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Numerical simulations of the flow and performance of a hydraulic Savonius turbine by the vortex in cell method with volume penalization

Uchiyama, T; Gu, Q; Degawa, T; Iio, S; Ikeda, T; Takamure, K

RENEWABLE ENERGY 157 巻頁： 482 - 490 2020年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Renewable Energy

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 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.

DOI： 10.1016/j.renene.2020.05.001

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Energy transition in air of a sphere launched vertically upward in water

Takamure K., Uchiyama T.

OCEAN ENGINEERING 207 巻 2020年7月

記述言語：日本語掲載種別：研究論文（学術雑誌）出版者・発行元：Ocean Engineering

In a present experiment, a solid sphere with a density of 2.64 × 103 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 effects of the submergence depth on the motion of the sphere and behavior of the air–water interface were investigated, which indicated that the Reynolds number immediately after the sphere passed through the air–water interface was Re¯w1∼3000 at all submergence depths (1.0d≤H≤6.0d; d is the diameter of the sphere and H is the submergence depth). The experimental values of the maximum displacement position were always smaller than the theoretical values owing to the energy dispersion caused by the water droplets entrained around the sphere. When the submergence depth was H∕d<3, the higher the submergence depth, the smaller was the rise of the sphere after passing through the air–water interface. However, when the submergence depth was H∕d≥3, the temporal changes in the vertical trajectory of the sphere were approximately equal. The energy ratio Ep∕Ek was defined as the ratio of the kinetic energy Ek of the sphere immediately after it passed through the air–water interface to the potential energy Ep when the sphere reached the maximum displacement position. Ep∕Ek decreased when the submergence depth was H∕d<3; however, it had a constant value of Ep∕Ek∼0.57±0.05 when the submergence depth was H∕d≥3. In addition, when the submergence depth was H∕d≥3, the ratio of each energy (kinetic energy, potential energy, and interfacial energy) became similar immediately after passing through the water surface. This indicated that each energy distribution had reached the equilibrium state. These findings contribute to the determination of variable parameters when modeling the water exit problem.

DOI： 10.1016/j.oceaneng.2020.107426

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Dynamics of impact cratering on granular bed by hydrogel sphere

Matsuda, Y; Kamiya, R; Yamaguchi, H; Uchiyama, T

PHYSICS OF FLUIDS 32 巻 ( 6 ) 2020年6月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physics of Fluids

A lot of studies on the dynamics of a granular impact cratering by a liquid drop have been carried out. However, the results so far are controversial due to the complex impact dynamics of a liquid drop, such as deformation, splash, and penetration into the granular bed. In this study, we focused on the dynamics of the granular impact cratering by a hydrogel sphere, which deforms without splashing and penetrating. We investigated the maximal deformation time of the sphere and the lift-off time of the grains. Both the maximal deformation time and the lift-off time are similar to each other and depend on the -1/2 power of the Young's modulus of the hydrogel sphere. This power law of the maximum deformation time is the same as an impact of a gel sphere on a flat solid surface. The angle of the ejected curtain was evaluated. The angle is larger for the impact with small deformation of the sphere than that for the impact with large deformation, and the angle is less dependent on the free-fall height. We also investigated the distributions of the ejected grains using the grains dyed by a fluorescent dye. The distribution was visualized by the fluorescent images captured before and after the impact. At the crater rim, the number of the dyed grains flying to and away are balanced. The number of the dyed grains gathered at the dimensionless distance from the crater center of 1.15, where the distance is nondimensionalized by the crater radius, is the largest. This maximum value for the number of the gathered grains is larger for the impact with small deformation than that with large deformation. This result is consistent with the dependence of the impact mode on the angle of the ejected curtain.

DOI： 10.1063/5.0011406

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Motion of a spherical particle in a microbubble plume and the behavior of microbubbles around the particle

Uchiyama, T; Kawasaki, Y; Degawa, T; Takamure, K

PROCEEDINGS OF THE INSTITUTION OF MECHANICAL ENGINEERS PART C-JOURNAL OF MECHANICAL ENGINEERING SCIENCE 234 巻 ( 7 ) 頁： 1340 - 1350 2020年4月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science

This study aims to investigate the motion of a solid spherical particle in a microbubble plume and the behavior of bubbles around the particle. Microbubbles (mean diameter 0.037 mm) released into a rectangular conduit by the electrolysis of water rise via buoyancy and form a bubble plume in the conduit. A solid spherical particle with a diameter of 10 mm and density of 1022 kg/m3 is placed on a mesh stretched across the cross-section near the bottom of the conduit, and microbubbles are then released from the cathode. Experiments are conducted with the bubble volumetric flux in the conduit j G at 0.05 and 0.09 mm/s. The particle repeatedly rises and falls when j G = 0.05 mm/s, and it rises almost vertically when j G = 0.09 mm/s. The absolute value of the vertical velocity of the particle is lower than that of the bubble. There is a belt-like region where the bubble velocity is extremely lower behind the particle. Such wake behind the particle clearly appears when the particle is falling, because the bubble velocity relative to the particle is higher.

DOI： 10.1177/0954406219893000

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Numerical simulation of bubbly flow around a cylinder by semi-Lagrangian-Lagrangian method

Nguyen, V; Degawa, T; Uchiyama, T; Takamure, K

INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW 29 巻 ( 12 ) 頁： 4660 - 4683 2019年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Numerical Methods for Heat and Fluid Flow

Purpose: The purpose of this study is to design numerical simulations of bubbly flow around a cylinder to better understand the characteristics of flow around a rigid obstacle. Design/methodology/approach: The bubbly flow around a circular cylinder was numerically simulated using a semi-Lagrangian–Lagrangian method composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase. Additionally, a penalization method was applied to account for the cylinder inside the flow. The slip condition of the bubbles on the cylinder’s surface was enforced, and the outflow conditions were applied to the liquid flow at the far field. Findings: The simulation clarified the characteristics of a bubbly flow around a circular cylinder. The bubbles were shown to move around and separate from both sides of the cylinder, because of entrainment by the liquid shear layers. Once the bubbly flow fully developed, the bubbles distributed into groups and were dispersed downstream of the cylinder. A three-dimensional vortex structure of various scales was also shown to form downstream, whereas a quasi-stable two-dimensional vortex structure was observed upstream. Overall, the proposed method captured the characteristics of a bubbly flow around a cylinder well. Originality/value: A semi-Lagrangian–Lagrangian approach was applied to simulate a bubbly flow around a circular cylinder. The simulations provided the detail features of these flow phenomena.

DOI： 10.1108/HFF-03-2019-0227

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Numerical simulation of fluid forces on moving solid body by the vortex in cell method with volume penalization

Degawa, T; Gu, Q; Uchiyama, T; Takamure, K

AEROSPACE SCIENCE AND TECHNOLOGY 94 巻 2019年11月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Aerospace Science and Technology

This study proposes a method for calculating the fluid forces acting on moving solid bodies in flows simulated by the vortex in cell (VIC) method. The body is represented using the volume penalization (VP) 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 taking the divergence of the Navier-Stokes equation. The pressure and viscous stress on the body surface are calculated using a quadratic function along the vector normal to the surface. This study simulates the flow around a cylinder oscillating in still water by the VIC-VP method, and calculates the fluid forces acting on the cylinder using the proposed method. The velocity profiles on four cross-sections at three different time points agree well with the results of a measurement. The in-line force acting on the cylinder also agrees with the existing results computed by a boundary-conforming formulation. These demonstrate the validity of the authors' method for calculating the fluid forces on solid bodies in flows simulated by the VIC-VP method.

DOI： 10.1016/j.ast.2019.105360

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Deformation of a vortex ring caused by its impingement on a sphere

Nguyen, VL; Takamure, K; Uchiyama, T

PHYSICS OF FLUIDS 31 巻 ( 10 ) 2019年10月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Physics of Fluids

The deformation of a vortex ring caused by its impingement on a sphere was numerically investigated using a proposed vortex-in-cell method. The method was validated by simulation of the collision of a vortex ring with a rigid planar surface and proved to be most satisfactory in the analysis of the dynamics of a vortex structure. In a coaxial collision, the behavior of the vortex structure is similar to that in the case of a planar surface. A secondary vortex ring is formed owing to the separation of the boundary layers on the sphere, caused by the effect of the primary vortex ring. The interaction between the secondary and primary vortex rings plays an important role in the dynamics of the vortex structure when the secondary vortex ring is completely formed. In a noncoaxial collision, the structure of the secondary vortex is moderately different from that in the coaxial collision. Moreover, the vortex structure in the coaxial collision is two-dimensional, in which the vorticity field is dominated by two transverse components, whereas that in the noncoaxial collision is three-dimensional. The total kinetic energy in both the cases decreases gradually during the entire period of evolution, whereas the enstrophy reduces in the early stage, then increases considerably, before a gradual reduction in the final stage. The enstrophy reaches a peak when the secondary vortex ring is completely formed, at which stage the effects of vortex stretching and vorticity production at the solid boundary are higher than that of vortex diffusion.

DOI： 10.1063/1.5122260

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Numerical simulation of the interaction between a vortex ring and a bubble plume

Nguyen, VL; Degawa, T; Uchiyama, T

INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW 29 巻 ( 9 ) 頁： 3192 - 3224 2019年9月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Numerical Methods for Heat and Fluid Flow

Purpose: This paper aims to provide discussions of a numerical method for bubbly flows and the interaction between a vortex ring and a bubble plume. Design/methodology/approach: Small bubbles are released into quiescent water from a cylinder tip. They rise under the buoyant force, forming a plume. A vortex ring is launched vertically upward into the bubble plume. The interactions between the vortex ring and the bubble plume are numerically simulated using a semi-Lagrangian–Lagrangian approach composed of a vortex-in-cell method for the fluid phase and a Lagrangian description of the gas phase. Findings: A vortex ring can transport the bubbles surrounding it over a distance significantly depending on the correlative initial position between the bubbles and the core center. The motion of some bubbles is nearly periodic and gradually extinguishes with time. These bubble trajectories are similar to two-dimensional-helix shapes. The vortex is fragmented into multiple regions with high values of Q, the second invariant of velocity gradient tensor, settling at these regional centers. The entrained bubbles excite a growth rate of the vortex ring's azimuthal instability with a formation of the second- and third-harmonic oscillations of modes of 16 and 24, respectively. Originality/value: A semi-Lagrangian–Lagrangian approach is applied to simulate the interactions between a vortex ring and a bubble plume. The simulations provide the detail features of the interactions.

DOI： 10.1108/HFF-12-2018-0734

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Numerical simulation of annular bubble plume by vortex in cell method

Nguyen, VL; Degawa, T; Uchiyama, T

INTERNATIONAL JOURNAL OF NUMERICAL METHODS FOR HEAT & FLUID FLOW 29 巻 ( 3 ) 頁： 1103 - 1131 2019年3月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：International Journal of Numerical Methods for Heat and Fluid Flow

Purpose: This study aims to provide discussions of the numerical method and the bubbly flow characteristics of an annular bubble plume. Design/methodology/approach: The bubbles, released from the annulus located at the bottom of the domain, rise owing to buoyant force. These released bubbles have diameters of 0.15–0.25 mm and satisfy the bubble flow rate of 4.1 mm3/s. The evolution of the three-dimensional annular bubble plume is numerically simulated using the semi-Lagrangian–Lagrangian (semi-L–L) approach. The approach is composed of a vortex-in-cell method for the liquid phase and a Lagrangian description of the gas phase. Findings: First, a new phenomenon of fluid dynamics was discovered. The bubbly flow enters a transition state with the meandering motion of the bubble plume after the early stable stage. A vortex structure in the form of vortex rings is formed because of the inhomogeneous bubble distribution and the fluid-surface effects. The vortex structure of the flow deforms as three-dimensionality appears in the flow before the flow fully develops. Second, the superior abilities of the semi-L–L approach to analyze the vortex structure of the flow and supply physical details of bubble dynamics were demonstrated in this investigation. Originality/value: The semi-L–L approach is applied to the simulation of the gas–liquid two-phase flows.

DOI： 10.1108/HFF-03-2018-0094

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FLOW PAST TWO CYLINDERS ARRANGED IN TANDEM WITHIN A MICROBUBBLE PLUME

Uchiyama, T; Kano, R; Degawa, T; Takamure, K

PROCEEDINGS OF THE ASME/JSME/KSME JOINT FLUIDS ENGINEERING CONFERENCE, 2019, VOL 5 頁： . 2019年

EXPERIMENTAL STUDY OF MIXING OF TWO-LAYER DENSITY-STRATIFIED FLUID BY A VORTEX RING

Cao, L; Ito, R; Degawa, T; Matsuda, Y; Takamure, K; Uchiyama, T

PROCEEDINGS OF THE ASME/JSME/KSME JOINT FLUIDS ENGINEERING CONFERENCE, 2019, VOL 5 頁： . 2019年

Development of a propeller-type hollow micro-hydraulic turbine with excellent performance in passing foreign matter 査読有り

Uchiyama, T., Honda, S. and Degawa, T.

Renewable Energy 126 巻頁： 545-551 2018年

Numerical simulation of jet issuing diagonally upward into density-stratified fluid in cylindrical tank 査読有り

Degawa, T., Uchiyama, T., Aozasa, I., Ishikawa, A. and Motoyama, K.

J. Power and Energy Eng. 6 巻 ( 3 ) 頁： 38-52 2018年

Smoothed profile-lattice Boltzmann method for non-penetration and wetting boundary conditions in two and three dimensions

Seta, T; Uchiyama, T; Takano, N

COMPUTERS & FLUIDS 159 巻頁： 64 - 80 2017年12月

記述言語：英語掲載種別：研究論文（学術雑誌）出版者・発行元：Computers and Fluids

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.

DOI： 10.1016/j.compfluid.2017.09.012

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Control of air bubble cluster by a vortex ring launched into still water 査読有り

Uchiyama, T., Kusamichi, S.

Int. J. Chemical Engineering and Applications 8 巻 ( 1 ) 頁： 37-46 2017年

Generation and transport of solid particle clusters using a vortex ring launched into water 査読有り

Uchiyama, T., Yano, C., and Degawa, T.

Int. J. Chemical Engineering and Applications 8 巻 ( 4 ) 頁： 253-260 2017年

Behavior of a jet issuing diagonally upward into two-layer density-stratified fluid in a cylindrical tank 査読有り

Degawa, T., Fukue, S., Uchiyama, T., Ishikawa, A., and Motoyama, K.

J. Flow Control, Measurement & Visualization 5 巻頁： 51-64 2017年

Study of the interactions between rising air bubbles and vortex core of swirling water flow around vertical axis 査読有り

Chemical Engineering Science 142 巻頁： 137-143 2016年

Numerical simulation of the interactions between a vortex ring and solid particles suspended above a horizontal wall 査読有り

301 巻頁： 966-980 2016年

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