The radiated noise from isotropic turbulence

The radiated noise from isotropic turbulence is analyzed on the basis of the Lighthill relationship, whereby the fourth-order Lighthill's stress tensor retarded-time covariance is evaluated from the square of a similar second-order covariance, which is assumed known. In this derivation no statistical assumptions are involved. This result, using distributions for the second-order space-time velocity squared covariance based on the direct numerical simulation results of both Sarkar and Hussaini (1993) and Dubois (1993), is compared with a reevaluation of Proudman's (1952) original model. These results are compared with the sound power derived from a phenomenological model based on sample approximations to the retarded-time/space covariance T(xx). The numerical solutions of Sarkar and Hussaini for the acoustic power are compared with the results obtained from the analytic solutions. (AIAA)