2015 年 81 巻 826 号 p. 15-00148
Intense tonal sound radiates from flows around a trailing edge with an upstream kink shape such as found in an automotive body. To clarify the acoustic radiation mechanism and the effects of the kink shape angle on tonal sound, direct numerical simulations (DNS) of flows and sound fields and wind tunnel experiments were performed. As a result, the feedback loop of the sound generation was clarified as below. A vortex is shed between the kink shape and the trailing edge, and convects downstream. The acoustic wave radiates from distortion of the vortex due to the interference with the wall around the trailing edge. The acoustic waves are propagated and lead to the vibrating of shear layers around the kink shape. The disturbances due to this vibrating are amplified in the downstream of the reception point of sound, and a vortex is again shed. The reception point is located slightly downstream of the flow separation point. The positions of the acoustic source and the acoustic reception in this feedback loop were also clarified. Meanwhile, the tonal sound dose not radiate for smaller kink shape angle, where the vortex formation does not occur around the kink shape by the lack of flow separation. Also, for the larger kink shape angle, the large separation prompts turbulent transition and the tonal sound does not radiate.
