A numerical study of sound radiation by isotropic turbulence is carried out by combining turbulence simulation with Lighthill's acoustic analogy. In the first study we analyze sound generation by decaying isotropic turbulence obtained both with 64 3 Direct Numerical Simulation (DNS) and 16 3 Large Eddy Simulation (LES). Both simulations lead to similar results for acoustic power, in agreement with the numerical results of Sarkar and Hussaini, but slightly different from theoretical predictions of Proudman and Lilley. In the second study we analyze sound generation by forced stationary turbulence, simulated with 128 3 DNS using a forcing scheme which preserves turbulence structure. The acoustic power computed from the stationary turbulence is in good agreement with results obtained for decaying isotropic turbulence. The acoustic spectrum shows that the characteristic frequency of the generated sound is approximately four times the inverse eddy turnover time. The contributions of different turbulence scales to the generated noise are computed separately from filtered velocity fields. For the low Reynolds number turbulence analyzed, the scales which most contribute to noise generation are 2–3 times smaller than the energy-containing scales and lie between the energy and dissipation-rate spectral peaks.
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Witkowska et al. (1997) studied this question.