永田 靖典

<p>The satellite communication system without ground antennas is highly beneficial to ease construction and maintenance of the ground station. To realize it, the Iridium communication service which is consisted of 66 satellites on the LEO (Low-Earth Orbit) is focused. The telemeter and command data are transmitted and received through the Internet, Iridium ground station, and Iridium satellites. Then, only a PC connecting to the Internet is required for the present telecommunication system. To demonstrate this concept, the EGG (re-Entry satellite with Gossamer aeroshell and GPS/iridium) nanosatellite mission was conducted in 2017, which is the first satellite operated via only the Iridium SBD (Short Burst Data) communication. In this paper, the communication performance of the Iridium communication applied to LEO satellite is investigated and the EGG mission result is described. Trajectory-based simulation shows that the present system will function well even under the Doppler shift criteria, though the available time rate will be degraded. Actually, it worked successfully on the EGG mission regardless of the satellite location. Moreover, the telemeter data was acquired in semi-real time manner on the atmospheric-entry phase, which is very difficult for the ordinary ground antenna system. This should be the important feature of the present system. </p>

<p>The electrodynamic heat shield is new type of heat protection system for atmospheric-entry vehicle, which utilizes the Lorentz force acting on the weakly ionized plasma flow inside the shock layer. A huge amount of calculation is necessary to estimate overall effect of the electrodynamic heat shield, because its effect interacts with the atmospheric-entry trajectory. In the present study, the Viscous Shock Layer (VSL) analysis method for electrodynamic heat shield is proposed for the quick analysis, which can calculate much faster than Navier-Stokes (NS) simulation. For this purpose, the VSL equations for the electrodynamic heat shield analysis are introduced under the ideal gas assumption, including circumferential momentum equation and Maxwell equations. The new method is also proposed to solve the new VSL equations. By the comparison to the NS simulation, the new VSL method gives good estimations of drag force and wall heat flux for wide ranges of interaction parameter and Hall parameter although the slight difference of wall heat flux at the stagnation point is observed. Therefore, the present VSL method could be applicable to the estimation tool of the electrodynamic heat shield effect. </p>

<p>In semiconductor production, efficiency and precision of the cleaning process are very important. In this study, we handle "Single Wafer Cleaner" that is one of the washing methods in the way of blowing air to a wafer with a turning disk at a high speed. However, the flow in the device becomes turbulent, which causes the problem that water drops and dusts re-attach to the wafer surface. Therefore, it is necessary to understand the flow in the device exactly to solve this problem. In previous studies, we experimented to establish the method of understanding the flow in the semiconductor wafer cleaner without a covering cup that is used for liquid splash preventing. In this study, numerical calculations were performed to observe the flow in the device to study influence of covering cup and find a suitable turbulence model to simulate the experiment.</p>

<p>We conducted numerical simulations of the benchmark experiments of the pump sump conducted by Matsui et al. (2006 & 2015) and compared the simulation with the experimental data to investigate the effects of turbulence model, grid density and detection method of the vortices. We determined a threshold of the gas-liquid fraction function of VOF method (α) and the second invariant of velocity gradient tensor (Q2) to detect the air-entraining and submerged vortices by using vorticity, respectively. This method well detected the vortices and well reproduced the experiments for the RANS simulation using SST k-ω model. Large eddy simulation using Smagorinsky model, however, was sensitive to the grid system and difficult to reproduce the experimental vortex structures even for the finest grid system having 3.7 mil-lion cells.</p>

<p>展開型柔軟エアロシェルは，将来の革新的な大気圏突入システムとして期待されている．我々のグループでは，カプセル形状の本体の周りに取り付けられる円錐形状の薄膜フレアと，その外周に取り付けられたガス圧で展開し形状を維持するインフレータブルリングで構成される，薄膜フレア型の展開型柔軟エアロシェルに注目して研究開発を進めてきた．本技術に対する我々の研究開発活動の特徴は，大気球実験，観測ロケット実験，国際宇宙ステーション/「きぼう」からの超小型衛星の放出機会など，各種フライト機会を利用し，その都度，フライト実験機を開発し，実際に飛行させることで，各要素技術のフライト環境での実証や大気圏突入システムとしての機能検証を行ってきた点にある．本稿では，展開型大気圏突入機の研究開発の紹介とともに，我々がこれまでに行ってきた各種フライト試験の概要について紹介する．</p>

<p>Fluctuating pressure (p' ) of a large-scale vortical structure generated in a semiconductor single wafer spin cleaner was detected by using microphone array. Twelve microphones were installed on the exhaust cover under the rotating disk of the cleaner with their interval of 7.5° or 15°. Power spectrum densities (PSD) of p' were compared with those of fluctuating velocity measured by PIV for various rotation angular velocities to identify fluctuations due to convection of the large-scale vortical structure. Good agreement of PSDs indicates that the large-scale structure could be detected by using microphone. Cross-correlation of p' measured at different positions revealed that the large-scale structure convected to the downstream in the rotational direction of the disk. The convection speed was about 12 % of the angular velocity of the rotating disk. Number of the vortex in the large-scale structure was also evaluated from the time-series p' data. Time-space contour map was made for p' based on the data measured at the different angular position, and showed periodical swept strip patterns. Presences of the strip patterns indicate the pressure disturbances were stably convected to the downstream. From this time-space map, two-dimensional Fourier transform efficiently extracted the number of vortices in the large-scale structure.</p>

<p>Numerical prediction of air-entraining and submerged vortices in pump sumps is important for engineering applications. The validation of pump sump simulations, however, still is not enough, because the simulations is very complicated; for examples, treatment of gas-liquid interface, detection method of the vortices and selection of turbulence model etc. We conducted numerical simulations of the benchmark experiments of the pump sump conducted by Matsui et al. (2006, 2016) and compared the simulation with the experimental data to investigate the effects of turbulence model, grid density and detection method of the vortices. We determined a threshold of the gas-liquid fraction function of VOF method (α) and the second invariant of velocity gradient tensor (Q₂) to detect the air-entraining and submerged vortices by using vorticity, respectively. This method well detected the vortices and well reproduced the experiments for the RANS simulation using SST k-ω model. Large eddy simulation using Smagorinsky model, however, was sensitive to the grid system and difficult to reproduce the experimental vortex structures even for the finest grid system having 3.7 million cells.</p>

<p>In semiconductor production, efficiency and precision of the cleaning process is important. In this study, we handle "Single Wafer Cleaner" that is one of the washing methods in the way of blowing air to a wafer with a turning disk at a high speed. However, the flow in the device becomes turbulence, which causes a problem that water drops and dusts re-attach to the wafer. It is necessary to understand the flow in the device. In previous investigations, we were able to get knowledge of the detection of vortices using numerical computation and Particle Image Velocimetry analysis in using the simplified experiment model. Therefore, we tried to understand the detection of large-scale vortices combining speed data and the unsteady pressure data. We measure pressure using microphones and perform the frequency analysis and cross correlation of the data. In doing so, we have get the knowledge of the vortical structure.</p>

<p>It is known that the critical Reynolds number of turbulent transition in the straight-pipe flow is about 2300. However, it is reported that turbulent transition is delayed when there are micro-bubbles in water. And the drag was reduced in same Reynolds number range. To confirm the effect of the drag reduction, it is important to make a laminar flow at the entrance of the test section. To keep flow stable, we ensure the long entrance section of about 4 m. Then we measured the differential pressure and calculated friction factor in the straight pipe with circular cross section. The inner diameter of the pipe is 20 mm. In this experiment, turbulent transition took place at the same Reynolds number range when we use water with micro-bubbles and without micro-bubbles.</p>

大気球シンポジウム 平成27年度（2015年11月5-6日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000044004レポート番号: isas15-sbs-004

大気球シンポジウム 平成27年度（2015年11月5-6日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000044012レポート番号: isas15-sbs-012

第46回流体力学講演会/第32回航空宇宙数値シミュレーション技術シンポジウム (2014年7月3日-4日. 弘前文化センター), 弘前市, 青森県形態: カラー図版あり資料番号: AA1530023006レポート番号: JAXA-SP-14-010

第46回流体力学講演会/第32回航空宇宙数値シミュレーション技術シンポジウム (2014年7月3日-4日. 弘前文化センター), 弘前市, 青森県形態: カラー図版あり資料番号: AA1530023011レポート番号: JAXA-SP-14-010

The aerodynamic force enhancement effect occurs by applying magnetic field around a reentry vehicle in a weekly-ionized flow behind the strong detached shock wave. Recently, this force enhancement effect was experimentally investigated using an expansion tube which can produce high speed and high enthalpy flow. Because aerodynamic force measurement is difficult due to short test flow period in expansion tube, drag measurement system which employed a piezofilm with fast responsiveness was developed in this study. This drag measurement system was calibrated using CO2 pulse laser and applied to experimental investigation on the aerodynamic force enhancement effect in expansion tube. The aerodynamic force acting on simple models in the flow produced by the expansion tube can be measured in this system. Additionally, the increase of the drag force due to magnetization in a weekly-ionized flow was observed.

We experimentally and numerically investigated large-scale structures formed by vortices in a single wafer spin cleaner. The Q-criterion identified the vortices developed in the cleaner as the flow regions with positive second invariant of the velocity gradient tensor obtained by both the PIV and LES. The time-series two-components PIV data shows that small-vortices were clustered near and under the edge of the rotating disk and were periodically emanated from there to the housing wall of the cleaner. The emanation frequency was increased with increasing in the angular velocity of the rotating disk. Three-dimensional LES reveal that six longitudinal vortices were spirally developed from under the edge of the rotating disk to the housing wall. This structure stably rotated slower than the disk speed. Fourier analysis of the LES data agreed with that of the PIV data. This supports that the passages of the stable spiral vortices on the PIV measurement region resulted in the periodical emanation of the clustered small-vortices observed in the PIV. Such a very large-scale spiral structure will induce reattachment of contaminants on the wafer surface, and should be destructed for development of much higher efficient cleaner.

大気球シンポジウム 平成26年度（2014年11月6-7日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000021009レポート番号: isas14-sbs-009

大気球シンポジウム 平成26年度（2014年11月6-7日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県資料番号: SA6000021010レポート番号: isas14-sbs-010

第45回流体力学講演会/航空宇宙数値シミュレーション技術シンポジウム2013 (2013年7月4日-5日. タワーホール船堀), 東京形態: カラー図版あり資料番号: AA0062268010レポート番号: JAXA-SP-13-011

平成24年度宇宙航行の力学シンポジウム（2012年12月13日-14日. 宇宙航空研究開発機構宇宙科学研究所）, 相模原市, 神奈川県資料番号: SA6000010028

平成24年度宇宙航行の力学シンポジウム（2012年12月13日-14日. 宇宙航空研究開発機構宇宙科学研究所）, 相模原市, 神奈川県資料番号: SA6000010033