青山 剛史

極めて複雑なシステムとなっている近年の航空機は，その開発において，設計変更による手戻りや認証試験の複雑化などに起因する開発スケジュールの長期化およびコストの増大が大きな問題となっている．その解決手段として，デジタル技術，特にDX技術が世界的に注目されている．もし我が国がこの潮流に乗り遅れると，海外OEMのTier 1事業において確立してきた不可欠なパートナーとしての地位を失いかねない．このような状況下，JAXAは「新たな航空機を創出する航空機ライフサイクルDX技術の研究開発」を航空技術部門の活動における三本柱の一つと位置づけ，2022年度から着手している．その後，2023年度には，「経済安全保障重要技術育成プログラム」の一環として公募されたNEDO事業に，「航空機の設計，認証，生産プロセスの革新とプロセス統合」のテーマが採択され，共同提案者とともに設計DX，認証DX，生産DXおよびプロセス統合（DXプラットフォーム）の課題に取り組んでいる．

In the present study, the interaction between a wind turbine tower and blades and its aerodynamic effect on the wake structure are investigated using the rFlow3D CFD code, which was developed by JAXA. NREL Phase VI experimental wind turbine is selected as the computational test case. The result shows the shed vortex from the tower does not affect the total wind turbine performance significantly. However, cyclic fluctuation of the aerodynamic load and the change of vortex structure behind the tower are captured clearly. The rotational flow and shed vortex from the tower cause the increase of turbulence intensity and irregular velocity distributions. This is considered as one of the key features for capturing the wake vortex breakdown accurately. It is shown that the tower and blade interaction is important for detailed wake investigation even in this upwind wind turbine case.

Insects generate sound by their flapping wings as a consequence of spatial and temporal changes of pressures on the wing surface and vortices generated by the wing motion. To clarify the mechanism of sound generation, hybrid method combining CFD techniques and acoustic analysis is incorporated here and detailed characteristics of flapping sound, e.g. directivity of transmission or spectrum distributions, are clarified.

JAXAではヘリコプタ飛行時の主要な騒音であるBVI(Blade Vortex Interaction)ノイズの予測システムであるMENTORを開発している。その中で先行するロータブレードが放出した翼端渦をBeddoseの渦モデルを用いてモデル化しているが、このモデルはブレードが作る誘導流中の渦の幾何学的な配置を実験結果に基づいてモデル化しており、計算コストを抑えながら実用的な精度で渦の影響を考慮できるメリットを持つ。しかしながら、渦の減衰の効果を含まないため、予測されたBVIノイズは実際の計測値に比べて過大評価される傾向があった。そこで、本研究ではBeddoseの渦モデルに渦の減衰の効果を取り入れて計算を行い、渦の減衰がBVI騒音に与える影響を評価した。

Two types of prediction tools for helicopter noise have been developed under the cooperative research between Advanced Technology Institute of Commuter Helicopter Ltd. (ATIC) and National Aerospace Laboratory (NAL) . One of them is a combined method of CAMRAD II, interpolation code for blade motion and wake geometry, aerodynamic code of 3D unsteady Euler solver, and aeroacoustic code based on Ffowcs Williams and Hawkings (FW-H) formulation. The other consists of CAMRAD II, 3D unsteady Euler solver using moving overlapped grid method, and FW-H code. The acoustic waveform of Blade-Vortex Interaction (BVI) noise predicted by the former tool is in good agreement with the experimental data of 1/7-scale model AH-1 Operational Loads Survey (OLS) rotor. This method is applied to investigate the effect of blade-tip shape on the intensity of BVI noise. As a result, it is shown that anhedral and swept-forward tip shapes effectively reduce the BVI noise of OLS rotor in a descent flight condition. The predicted Effective Perceived Noise Level (EPNL) of a helicopter is also compared with the experimental data obtained by ATIC and reasonable correlation is obtained. The latter tool successfully predicts the distinct spikes in the BVI wave-form of ATIC model rotor tested in German-Dutch Wind Tunnel (DNW) . In the comparison of measured and calculated carpet noise contours, reasonable agreement is obtained. The present tools are expected to be useful for the design of low-noise helicopters in the future.