角柱近傍の平板が流れ場と音場に及ぼす影響

概要

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In studying the mechanism of aerodynamic noise generated by the body of an automotive vehicle, it is necessary to consider the effects of not only an object in the air flow, but also the body surface located close to the object on the noise. In the present paper, a square cylinder and a flat plate were employed as a test model, and aerodynamic noise in the far field and pressure fluctuations on the flat plate were examined by changing the distance between the square cylinder and the flat plate. A commercial, numerical simulation code based on Lattice Boltzmann Method was used to obtain the data on the flow structure and aeroacoustic properties. In parallel with this numerical simulation, an experiment was conducted with regard to this model. It was found from the experiment that the aeolian sound is generated by Karman vortices when the clearance between the square cylinder and the flat plate is 60% height or more of the square cylinder. In addition, the flat plate plays a role of an acoustic reflection surface. The effect of the flat plate on the far field noise level appears in the frequency region with St =0.25 or more, and an increase in the noise level by the acoustic reflection is about 5dB. Therefore, it is necessary to consider the non-compact acoustic characteristics to estimate the far field noise level.