Abstract
The characteristics of sound sources are analyzed by Lighthill equation based on the direct numerical simulations of compressible isotropic turbulence to investigate the physical mechanisms of the noise from fine scale turbulence and their interactions with shocklets. We study mainly on the compressibility effects on the sound source terms in Lighthill equation by comparing various turbulent Mach numbers (M_<t0> = 0.1 to M_<t0> = 1.0), where the sound source terms are decomposed into the Reynolds stress, entropy, and viscous term. We show that the Reynolds stress term is the most contributer to the overall sound sources for all Mach number cases, on the other hand, the sound level of viscosity term is very small. Also the characteristics of sound sources are changed due to the generation of shocklets for high Mach number cases. For low Mach number flows, the Reynolds stress term and entropy term has positive correlation so that the overall sound level is intensified. However, for high Mach number flows, the overall sound level is weakened because the negative correlation between the Reynolds stress term and entropy term becomes stronger and they partially cancels out each other.
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