大山 聖

<p>火星探査航空機は，将来の火星表面探査の画期的なシステムとして期待されている．しかしながら，火星の大気密度は地球と比べ1/100程度しかなく，得られる揚力は極端に小さい．そして，その飛行領域は低レイノルズ数環境として知られており，航空機の空力特性は大幅に悪化することが知られている．我々のグループでは，火星探査航空機を実現するために，この低レイノルズ数環境下での様々な空力課題に取り組んでおり，その解決に向けて実験/CFDの両面から取り組んでいる．また，実際に飛行試験機を作製し，大気球による高高度飛行実証試験（Mars Airplane Balloon Experiment-1, MABE-1）を通して，実フライトにおける空力データの取得にも取り組んでいる．本稿では，まずWGで取り組んでいる火星探査航空機の概略と空力課題の例および現状を紹介し，続いて，飛行試験の概要と結果の概略を報告する．</p>

第34回宇宙構造・材料シンポジウム（2018年12月4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: SA6000137024レポート番号: B02

大気球シンポジウム 平成30年度（2018年11月1-2日. 宇宙航空研究開発機構宇宙科学研究所 (JAXA)(ISAS)）, 相模原市, 神奈川県著者人数: 15名ほか資料番号: SA6000128031レポート番号: isas18-sbs-031

The present study experimentally proposes separation control around a pitching airfoil with burst (duty cycle) actuation of a wide range of the burst frequency using a dielectric barrier discharge plasma actuator. Experiments are conducted using a two dimensional NACA0015 (c = 100 mm) airfoil with the chord based Reynolds number of 63,000. The airfoil pitches from 5 deg to 25 deg with fluctuation frequency of 2 Hz corresponding to reduced frequency of 0.02π. A plasma actuator are installed at the leading edge and driven in continuous and burst modes with F+ = 0.5 - 60. Flow field is evaluated with unsteady pressure measurement. From the results, three control effects 1) delay of dynamic stall, 2) CL increase in the pitch-down phase, and 3) promotion of reattachment in the pitch-down stage are observed in burst actuation for a pitching airfoil.

Aerodynamics optimization of airfoil for flying-wing type Mars airplane is conducted to show tradeoff between maximization of aerodynamic performance and stability requirement. To see the tradeoff between the two objectives, a multiobjective evolutionary algorithm is used where aerodynamic performance of each airfoil is evaluated with a two-dimensional laminar Navier-Stokes flow solver. Some design constraints are applied to obtain feasible airfoil shapes. The obtained Pareto-optimal airfoils show tradeoff between the two design objectives. Analysis of the flow field of the obtained airfoils leads to some useful knowledge in designing airfoil for flying-wing type Mars airplane.

A generic framework for incorporating constraint handling techniques (CHTs) into multi-objective evolutionary algorithms (MOEAs) is proposed to resolve the differences between MOEAs from algorithmic and implementation perspective with respect to the incorporation of CHTs. To verify the effectiveness of the proposed framework, the performances of the combined algorithms of five CHTs and four MOEAs on eight constrained multi-objective optimization problems are investigated with the proposed framework. The experimental results show that the outperforming CHT can vary by constrained multi-objective optimization problems, as far as examined in this study.

© 2018, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved. We propose to use a helicopter for exploration of pit craters and caves on Mars. Helicopter does not contaminate inside of pit craters and caves because it does not emit gas including carbon compounds. In addition, a helicopter can explore caves even if the bottom of the caves is covered by rocks. We propose to explore the pit craters found near Elysium Mons because they are suitable for the aerial exploration because (1) there is higher possibility of existence of life and (2) air density is relatively high. We consider two specific missions using a helicopter; one is a mission which explores only a pit crater and the other is a mission which explores both a pit crater and a cave. The present analysis shows both missions are feasible.

© 2018, AIAA Aerospace Sciences Meeting. All rights reserved. Large-eddy simulations are conducted to investigate the control effects of a dielectric barrier discharge plasma actuator on a dynamic flowfield with a Reynolds number of 2.56 × 105 and a reduced frequency of 0.02π. The objective flowfields include dynamic stall phenomenon, flow separation and reattachment. First the flowfield without control is investigated and it is found that dynamic stall process can be classified into five stages; formation of a laminar separation bubble, breakdown of the laminar separation bubble which triggers formation of a dynamic stall vortex, convection of the dynamic stall vortex, full stall from the leading edge, and recovery to the attached state. Then the control effects with three burst frequencies (F +) of 0.5, 6, and 50 in nondimensionalized value are investigated. The DBD plasma actuator successfully enhances the cycle-integrated aerodynamic performances of the airfoil and major control effects are summarized into three; delay of dynamic stall, enhancement of aerodynamic forces during full stall by large vortices, and promotion of reattachment. The most effective burst frequency for each control effect differs from each other, showing that the best case for delaying the dynamic stall onset is the case with F + of 50 while the best case for promoting the reattachment is the case with F + of 6. The results show that the promoting the reattachment is effective for improving the cycle-integrated net damping and shortening the duration under the stall. For further improvement, the current results give a strong prospect of a closed-loop control in which F + is adapted to the change in the flowfield.