Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society for Aeronautical and Space Sciences  

DOI： 10.2322/tjsass.66.10

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CiNii Research

Authorship：Lead author,　Corresponding author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s00193-022-01079-1

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Other Link： https://link.springer.com/article/10.1007/s00193-022-01079-1/fulltext.html

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

In this study, three-dimensional numerical simulations and experiments of the interaction between a normal shock and bubbles generated by the repetitive energy depositions of a laser pulse in a Mach 1.92 flow was conducted. As a result of the shock–bubble interaction, a vortex ring, caused by a baroclinic effect, was generated. Owing to the self-induced velocity field, the advection velocity of the vortex rings decreased with increasing laser pulse energy. In the experiments, when interactions among the vortex rings became strong, separations in transverse directions between adjacent bubbles were induced. This was reproduced through numerical simulations by imposing an artificial disturbance in the initial positions of the bubbles, i.e., by 5% of the bubble diameter in a transversal direction. The asymmetric behaviors of a row of vortex rings were classified into three patterns based on the ratio of the distance between the vortex rings to the size of the vortex rings ( λ: inverse Strouhal number). In pattern 1, with λ >2.9, there was negligible interference between the vortex rings because the interval of the vortex rings was sufficiently large. In pattern 2, with λ = 0.97–1.2, separation in the vortex-ring rows appeared, and the separation angle increased as λ decreased. In pattern 3, with λ <0.62, the interference intensified, and the vortex rings collapsed, forming a turbulent flow behind the shock wave.

DOI： 10.1063/5.0083596

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

To achieve high-thrust-density operation, we propose electrostatic-magnetic hybrid ion acceleration in which the empirical thrust density limit of the electrostatic acceleration is surpassed without violent plasma oscillation by combing the collisional momentum transfer mechanism, which is the ion acceleration mechanism of the electromagnetic acceleration. To achieve hybrid ion acceleration, we experimentally obtained two design criteria: one near anode propellant injection and another at the on-axis hollow cathode location. The thrust characteristics of three thrusters composed of a slowly diverging magnetic field between an on-axis hollow cathode and a coaxially set ring anode were examined. By injecting xenon propellant along the anode inner surface, the electron impact ionization process was enhanced, and generated ions are electrostatically accelerated through the radial-inward potential gradient perpendicular to the axial magnetic lines of force. The hybrid ion acceleration characteristics were obtained only if these two criteria were satisfied and the obtained thrust was consistent with the thrust formula derived for steady-state, quasi-neutral plasma flows. In addition to the criteria, strengthening the magnetic field and enhancing the propellant mass flux were effective for improving thrust density without deteriorating thrust efficiency. Among the experimental conditions in this study, the maximum thrust density was 70 N/m2 with an anode specific impulse of 1200 s, which cannot be achieved in a purely electrostatic thruster with thrust density 6.3 times than that of a typical Hall thruster.

DOI： 10.1063/5.0066083

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Authorship：Lead author,　Corresponding author   Language：Japanese   Publisher：AIP Advances  

We evaluate the energy conversion efficiency of an electrical exploding foil accelerator that accelerates a thin dielectric foil (called the flyer) to more than 1 km/s, which is propelled by electrically exploded bridge material. The effective flyer mass ejected from the accelerator is estimated by impulse measurements obtained using a gravity pendulum as well as by time-resolving flyer velocity measurements obtained using a photonic Doppler velocimetry system. For two different bridge sizes (0.2 and 0.4 mm), the flyer velocity and impulse increase with the input energy at the bridge section. The maximum flyer velocity and impulse, that is, 4.0 km/s and 67 µN s, respectively, are obtained by supplying 0.33 J of input energy. Upon increasing the input energy, the effective flyer mass also increases and exceeds the designed-bridge mass for both bridge sizes. The energy conversion efficiency from input electrical energy to flyer kinetic energy is calculated based on the effective flyer mass, velocity, and input energy. Both bridge sizes show comparable efficiencies: 27% and 30% for 0.2 and 0.4 mm bridges, respectively. The efficiency increases with increasing specific input energy at least up to 15 MJ/kg for the 0.4 mm bridge, whereas the efficiency of the 0.2 mm bridge above 30 MJ/kg decreases. This is owing to the excessively high input energy density in the 0.2 mm bridge, which causes the effective flyer mass to increase by including surrounding materials. These results indicate that the specific input energy should be optimized for obtaining maximum efficiency.

DOI： 10.1063/5.0061699

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Event date： 2023.3

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：産業技術総合研究所 つくば中央   Country：Japan  

Event date： 2023.1

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：宇宙科学研究所   Country：Japan  

Event date： 2018.1

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Georgia Institute of Technology   Country：United States  

Event date： 2017.10

Language：English   Presentation type：Oral presentation (general)  

Venue：Georgia Institute of Technology   Country：United States  

Applicant：株式会社デンソー，株式会社日本自動車部品総合研究所，国立大学法人名古屋大学

Application no：特願2014-244196  Date applied：2014.12

Announcement no：特開2016-107175  Date announced：2016.6

Country of applicant：Domestic  

集中講義方式で実施する．はじめに航空機，ロケット，人工衛星の概論的な解説を行い，その内容を参考に設計するテーマを決めて設計を行う．設計結果は設計報告書にまとめるとともに，発表会で発表する．

講義で習得した原理や法則を体験的に理解し、実験装置や各種測定機器の作動原理、操作法など実験の方法を修得する。また、実験結果の整理、分析を通して科学技術報告書の作成法を学ぶ。