Study on Generation Mechanism and Control of Aerodynamic Noise Radiated from Longitudinal Vortex

2019 Fiscal Year Final Research Report

• Project/Area Number: 17K06174
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Fluid engineering
• Research Institution: Kure National College of Technology
• Principal Investigator: Ogawa Shigeru 呉工業高等専門学校, 55401, 嘱託教授 (90714262)
• Project Period (FY): 2017-04-01 – 2020-03-31
• Keywords: 縦渦 / 空力騒音 / 渦度 / 流れ場 / 音場 / 二重極音 / 音場解析 / 時間微分圧力変動

Outline of Final Research Achievements

The study aims to clarify the mechanism of how longitudinal vortex induces aerodynamic noise.
Based on the theory of Lighthill-Curle equation, the noise was estimated in the far field and compared with the experimental data. The result shows that the noise source is dipole noise. The measurement of noise source was experimentally conducted with beamforming method. The method clarified noise source distribution, which indicates that the dominant noise source is located at the apex of the vortex. The simulation was employed to relate flow field with noise field. As a result, it was found that although the flow field has the strongest vorticity at the apex of the vortex, the vorticity itself has little relationship with time derivatives of surface pressure fluctuations. Time derivatives of the vorticity have the strong correlation with time derivatives of surface pressure fluctuation. This new findings indicate that dominant noise source was located a little far away from the apex itself.

Free Research Field

音響流体力学

Academic Significance and Societal Importance of the Research Achievements

学術的意義として、縦渦から放射される空力騒音に関する、理論・実験・解析の三領域から総合的な知見が得られた。特に、低マッハ数・高レイノルズ数の流れ場の領域の音源は二重極音源であるとする理論が縦渦の音源にも適用でき、また音源は縦渦先端に局所的に存在していること、そして二重極音源に直接な影響を与えているのは渦度ではなく、渦度の時間微分であること等が解明でき、今後の音源探査に役立つものと考えられる。
社会的意義としては、自動車・新幹線・飛行機などの高速の乗り物や風車などには、縦渦が共通項として存在する。今回得られた知見を活用して騒音の低減策に繋げられれば、共通の対策効果が期待できるため波及効果も大きい。