乱流境界層内のキャビティ音発生におけるフィードバック機構 : 第2報,流体共鳴振動(流体工学,流体機械)

概要

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The fluid-acoustic interactions and the role of the acoustic resonance are clarified for the fluid-resonant oscillations in turbulent cavity flows by directly solving the compressible Navier-Stokes equations. The upstream boundary layer is turbulent, and the freestream Mach number is 0.15 or 0.3. The computational results are validated by experiments done in a low-noise wind tunnel. The depth-to length ratio of the cavity is varied from 0.9 to 2.5 and the results are compared with those of the fluid-dynamic oscillations, which take place in a shallow cavity with the depth-to-length ratio of 0.5. It is clarified that the mechanisms of the formation of large-scale vortices and the radiation of acoustic waves are essentially the same as those in the fluid-dynamic oscillations. However, the feedback loop is formed via a standing wave due to the acoustic resonance in the fluid-resonant oscillations, while a standing wave is not generated in the fluid-dynamic oscillations. The acoustic resonance amplifies the acoustic energy radiated by the collision of the vortices along the downstream wall. Moreover, the acoustic feedback becomes more intense due to the acoustic resonance. As a result, the fluid-resonant oscillations occur even at a low Mach number such as 0.15. Moreover, the effects of the cavity depth on the frequency as well as the amplitude of the fluid-resonant oscillations are clarified.
2010-05-25