79 巻 (2013) 804 号 p. 1419-1433
To clarify the mechanism of acoustic radiation in flows around a cascade of flat plates, fluid structures and acoustic fields were elucidated by direct simulations. The simulations were mainly performed for flows around 5 parallel plates and the separation-to-thickness ratio s/d was 6.0. The freestream velocity was changed from 30 m/sec to 60 m/sec, and the acoustic resonance occurs between plates at the freestream velocity of 44 m/sec. At that velocity, the Reynolds number based on the chord length and the freestream velocity was 8.7×104 and that based on the plate thickness was 5.8×103. Computational results were validated by the experimental results performed in the present research. The computational results showed that large-scale vortices composed of fine-scale vortices are shed in the wakes of the plates independently of the acoustic resonance. When the large-scale vortex is shed from the upper or lower face, an expansion wave is radiated around the downstream edge of the upper or lower face, respectively. The compression wave is radiated around the downstream edge of the opposite face. The simulation for the flow around a single plate was also performed, and the results confirmed the above-mentioned acoustic radiation mechanism. For the flows around a cascade of flat plates, the sheddings of the vortices from neighboring plates are synchronized when the acoustic resonance occurs. It was also clarified that the mode of the synchronization is an anti-phase mode and the standing waves generated between plates are reinforced.