Sound Generation by Interactions among Vortex, Heat and Shock Wave

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Generation mechanism and natures of sound through vortex, heat and shock wave interactions are studied both computationally and experimentally. Inoue developped a highly-accurate, compressible Navier-Stokes code (6th-order in space and 4th-order in time) and applied it to shock-vortex interauction problems. The results show that, (1) three sounds are generated successively by the interaction between a single vortex and a plane shock wave, (2) each sound has a quadrupolar nature, and (3) the strengths of the sounds depend both on the strengths of a shock wave and a vortex. Inoue also applied the code to the interaction between a pair of vortices and a shock wave, and clarified that the number of sound generated by the interaction and the characteristic naturcs of the sounds depend on whether the pair of vortices moves in the same direction as the shock wave or opposite to it. Inoue also studied compressible flowfields around a helicopter and clarified the characteristic natures of the f … More lowfields in a vortex ring state and in an autorotation state for the first time. The results suggest strongly that the sound generation in the helicopter rotor flowfield is closely related to the interaction between the tip-vortices and the rotor baleds. Fukunishi imposed a sound wave on a turbulent boundary layr, and examined the vortical motion in the boundary layr. Fukunishi found that the turbulent boundary layr can be effectively excited by the sound wave. Sasoh studied experimentally the sound noise at the exit of a tunnel produced by a highspeed bullet train (Shinkansen), and found that attenuation of a shock wave produced by a Shinkansen is inevitable to reduce the sound noise. Sasoh proposes the use of pseudo-perforated walls in a tunnel. By using a two-dimensional Navier-Stokes code, Ju studied numerically flowfields produced by the interaction of premixed gases of H2 and air with a shock wave, and found that the so-called Richtmyer-Meshkov instability plays an important role in the generation of vortices and thus the generation of sound. Hattori simulated numerically sound pressure fields generated by the head-on collision of two vortex rings, and found the following important results. (1) When the strengths of the two vortex rings are equal, two sounds are generated and each sound has quadrupolar nature. (2) When the strengths of the two vortex rings are not equal, four sounds are generated and the direction of the sound propagation is affected by the difference of the strengths of the two vortex rings. Hattori and lnoue also studied the characteristic natures of sound generated by oblique collisions of two vortex rings, and captured numerically the generation of octupolar sounds. Less