Study of Acoustic Sounds by Computational and Experimental Fluid Dynamics

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Acoustic sounds observed in four different fields of fluid dynamics are studied by four experts independently. Each expert in a field is supported by the other three experts in other fields who have different ideas, methods, know-hows and experiences, respectively. Inoue studied sounds produced by vortex-vortex interactions and shock wave-vortex interactions by 2D/3D direct Navier-Stokes simulations, and clarified the quadrupolar natures of sounds by the interactions. He also studied the 3D compressible flows around helicopter rotors and captured numerically vortex ring states and auto-rotation states for first time which are closely related to helicopter noises. Hayase studied numerically unsteady 2D flows in an orifice and also through spool valves, and showed that acoustic sound produced in these flows are closely related to the behavior of vortices. Sasoh studied experimentally tunnel sonic booms produced by highspeed trains, and showed that the booms are directly related to shock waves generated by entrance of a train in a long tunnel. Tsubota studied acoustic sounds in superfluid Helium and clarified that generation of quantized vortices is one of the sources of sounds in low temperature flow fields. The results obtained by the four experts are compared with each other. It is found that there are common natures among the sounds observed in spite of the difference of the flow fields studied ; for example, sounds produced by vortex-vortex interactions and vortex-sounds interactions have quadrupolar natures while dipolar property is predominant when obstacles or walls exist.