Basic research of the generation mechanism of aerodynamic noise-Development to complex flow fields and control of the noise-

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In this project, the generation and propagation mechanisms of aerodynamic noises generated in complex flow fields have were investigated. Inoue and Hatakeyama developed a highly-accurate finite difference numerical scheme (8-th order accurate in space and 4-th order in time) to solve the unsteady compressible Navier-Stokes equations. They applied the scheme to noise problems generated by multiple bodies placed in a uniform flow and found that flow and sound fields vary drastically depending on the spacing between the bodies. For the case of two bodies placed in tandem in a uniform flow, they found that the amplitude of sound waves is greatly suppressed (up to 1/50 of the single body case) or enhanced (up to ten times as large as the single body case), depending on the spacing of the bodies. For the case of two bodies in a side-by-side arrangement, they found that 6 different patterns of flow and sound fields appear depending on the spacing of the bodies. In both cases of tandem and side-by-side arrangement, bifurcation phenomenon was observed depending on initial conditions. These results strongly suggest a possibility of noise control. For the case of three bodies in a side-by-side arrangement, a beat of sound was observed. Fukunishi found experimentally that cavity noise can be suppressed significantly by placing a control panel in the cavity and suggested the possibility of turbulence control by this method. Nakamura investigated numerically supersonic jet noise problems and clarified the generation and propagation mechanisms in some detail. Ishii developed a highly-accurate new computer code and applied it to cavity noise problems. He clarified the importance of the span-length on the generation of the cavity noise.