Acoustic Behavior Of The Turbulence

In this paper, an experimental research on the acoustic behavior has been deduced. Since coherent structures in the jet flow could be taken as a stationary coherent acoustic sources with phase randomness, a mathematical relationship is obtained by the Fourier transform between the Lighthill stresses in the source region as a solution of the Lighthill equation in the frequency domain and the acoustic pressure distribution on a spherical surface with radius large enough in the wave length domain, under the foundation of systematic checking to Laufer-Yen's experiment, we get that the farfield acoustic radiation measured in this experiment with strong antenna effect coincode with the dipole-antenna effect obtained by a Fourier transform to the Lighthill stress dominant with its linear terms.Experimental measurement on the Lighthill stresses in the image of the acoustic source region reconcentrated by a spherical surface with a diameter ratio to the jet exit of 450:1 demonstrates that the normal Lighthill stresses T xxand Tr rare one order larger than the shear stresses, which consists with the original analysis of Ffowcs Williams and Kempton, where the directivity factor of the antenna effect is approximately equal to ? k2l2, the amplitude distribution of T xx or Tr r along axial could be fitted with a Gaussian curve, and its characteristic length scale consists with that measured in the source region. A high level of background noise mixed with the radiation of the coherent structures should be excluded, its level could be related with the value measured in the farfield, such that atθ=90.