大山 聖

レポート番号: Ⅱ-2

第53回流体力学講演会/第39回航空宇宙数値シミュレーション技術シンポジウム (2021年6月30日-7月2日. 日本航空宇宙学会 : 宇宙航空研究開発機構(JAXA)オンライン会議) The 53rd Fluid Dynamics Conference / the 39th Aerospace Numerical Simulation Symposium (June 30 - July 2, 2021. The Japan Society for Aeronautical and Space Sciences : Japan Aerospace Exploration Agency (JAXA), Online meeting) In this paper, aerodynamic characteristics around the blade of the hexacopter ''HAMILTON (HexAcopter for Martian pIt crater exploraTiON)'' for Mars exploration are investigated to obtain design knowledge regarding multicopter drone flying in Martian atmosphere. Reynolds-averaged Navier-Stokes simulation with the moving overlapped grid was employed for aerodynamic evaluation of two cases; one is hexa-rotor case and the other is single rotor case in order to compare single rotor case and hexa-rotor case and reveal unique characteristics of multirotor case. According to computational results, in both cases, hexa-rotor and single rotor, the maximum figure of merit could be observed at higher hovering thrust conditions. It is suggested that the baseline blade geometry could generate thrust efficiently at higher thrust conditions. The flow structure around the hexa-rotor can be classified into three groups; turn-in side where the flow was drawn the inside by blades rotation, turn-out side where the flow was put out to the outside by blades rotation, and the center side which was located between the turn-in and turn-out sides. The rotors of the center side took the low figure of merit compared with the other rotors because of aerodynamic interference from the turn-in side and the turn-out side rotors. Therefore, the total figure of merit of all rotors increased when the distance among rotors is increased. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA2130027012 レポート番号: JAXA-SP-21-008

In this study, AC DBD plasma actuator is applied to control the flow around NACA0015 and Ishii airfoils in a low Reynolds number condition (Re = 63,000). Here, the Ishii airfoil is a high performance airfoil at the low Reynolds number condition. The DBD plasma actuator is located at x/c = 5% and is actuated in burst mode with the nondimensional burst frequency F+ from 0.1 to 20. Maximum control authority is achieved with Vpp = 6kV and F+higher than 6 for both airfoils. Results show that different effect of separation control between NACA0015 airfoil and Ishii airfoil.

The convective Mach number and density ratio dependences of sound sources and flow structures in a compressible mixing layer are investigated by direct numerical simulations. Characteristics of sound sources are analyzed using the source terms of Lighthill equation. As the Mach number increases sound source strength decreases, because vortex motion is weakened by compressibility. For density ratio dependence, the emission angle of Mach waves becomes shallower and vortices show sparse structures as density ratio increases. In addition, larger vortex structures appear at lower density side for higher density case.

Large-eddy simulations of the separated flow over an NACA0015 airfoil controlled by the DBD plasma actuator are conducted and the flow fields and the aerodynamic performances are compared with the Ishii airfoil, one of the high performance airfoil at the low Reynolds number. The DBD plasma actuator is set at the 5% chord length from the leading edge of NACA0015 airfoil and operated in burst mode at the Reynolds number Re=63,000. In both cruise and post stall angle of attack, Ishii airfoil show higher aerodynamic performance than NACA0015 airfoil when DBD plasma actuator is OFF. However, when the DBD plasma actuator is activated, NACA0015 show higher aerodynamic performance.

DESTINY is injected to long elliptical orbit by Epsilon rocket launcher. If the apogee altitude of the injected orbit is high enough, it is achieved to ease the requirements for design and operation of the spacecraft. This paper investigates the ability of trajectory injection by means of 4-stage Epsilon rocket using the method of multi objective optimization under several flight constraints.

"DESTINY" is an acronym of "Demonstration and Experiment of Space Technology for INterplanetary voYage", which is proposed by JAXA/ISAS as "ISAS Small Scientific Satellite" mission. In this mission, trajectory design is one an important technical element because of its many revolution low-thrust orbits with many mission objectives and constraints. Evolutionary computation is utilized to find candidates for the orbit.

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Aerodynamic characteristics of reusable observation vehicle are computationally investigated under subsonic and supersonic flows using the RANS (Reynolds-averaged Navier-Stokes) simulations. The initial investigation for the concept design is done with the light optimization using the light CFD. The results show that the simulations using coarse grid estimate the axial force coefficient and the lift to drag ratio accurately except some cases. The results indicate the correlation between the supersonic lift to drag ratio and the axial force coefficient. The results show the correlation between the y-coordinate of the design variable and the volume. The required knowledge for the concept design in the near future is obtained.

PARSEC airfoil parameters often used for transonic airfoil design are re-examined by data-mining Pareto-optimal airfoil designs. The Pareto-optimal airfoils are obtained by using a multiobjective evolutionary algorithm. For data mining, scatter plot matrix coupled with correlation coefficient is used. The present result shows that the PARSEC airfoil parameters may not be the best choice for transonic airfoil design. The result also indicates that data mining from Pareto-optimal airfoils may give more information than data mining from all feasible airfoils.

The performance of the surface air-flow induced by non-thermal plasma is studied experimentally. The non-thermal plasma is generated by atmospheric dielectric-barrier discharge. The input discharge power was 1.8W. At first, flow induced by the discharge on a flat plate is investigated. Velocity profile is measured by a hot-wire anemometer. The maximum value 1.1 m/sec was observed on the plate surface. Secondary, separation control for wing surface flow is investigated using a 9cm chord NACA0015 in a wind tunnel at 20m/s of air stream velocity (Re〜1.2x10^5). Barrier discharge electrode is set on the leading edge of the wing. Separation angle is increased by 3.5 degrees and the maximum of the lift coefficient is improved by 12%.

This paper describes recent activity in JAXA aiming reformation of design and development (D & D) process by introduction of information technology, simulation technology, reliability engineering, etc for rocket valve reliability improvement. In this activity, JAXA's information system for rocket valve D & D will be developed by the end of FY2007. This information system consists of detailed FMEA/FTA utilization support tool, QFD utilization support tool, and material database system and material database utilization support tool. This information system will help to improve efficiency and reliability of D & D process of JAXA's rocket valves and other JAXA's products.