Aerodynamic Sound Sources from Flows around a Rectangular Cylinder with a Low Mach Number

Abstract

In order to clarify dominant aerodynamic sound sources with regard to the sound generated from flows around a rectangular cylinder, decoupled simulations based on Lighthill's acoustic analogy are performed. The freestream Mach number is 0.2 and 0.4, and the Reynolds number based on the side length and the freestream velocity is 150. In these decoupled simulations, acoustic fields are predicted by the acoustic simulations using Lighthill's tensor, which is computed by incompressible flow simulations. It is clarified that the predicted acoustic fields are in good agreement with those by direct simulations. Moreover, it is presented that the shift of the propagation angle of the acoustic waves due to the Doppler effects can be captured by the present decoupled simulations. Also, the scattered sound is predicted by the force exerted on the flow by the cylinder, which is computed by the results of the above-mentioned decoupled simulation. The direct sound is computed by subtracting the scattered sound from the total sound. As a result, the effects of the freestream Mach number on the contributions of the scattered and direct sounds to the total sound are clarified. Moreover, by investigating the effects of filtering out a part of the acoustic sources in the wake on the predicted acoustic fields, the dominant acoustic sources contributing to the far acoustic field are identified.