Sound radiated by turbulence - acoustic analogy validation

Predicting sound radiated by turbulence is of interest in many applications including aeroacoustics, hydroacoustics, and combustion noise. Significant improvements in computer technology in recent years have renewed interest in applying numerical techniques to predict the sound from turbulent flows. One such technique is the hybrid acoustic analogy approach in which the turbulence is computed using a method such as direct numerical simulation (DNS) or large eddy simulation (LES), and the sound is calculated using an acoustic analogy. The objective of this study is to evaluate the hybrid approach for predicting sound from broadband turbulence at low turbulent Mach number using the Lighthill acoustic analogy.;Initial investigations study the effects of source spatial periodicity in an acoustic-analogy calculation. Since many applications of turbulence DNS or LES assume spatial periodicity in one or more directions, understanding such effects is important. In addition, the Lighthill acoustic analogy is validated for a two-dimensional, forced turbulent monopole source by comparison of DNS results with acoustic-analogy predictions.;A primary objective of this dissertation research is to validate the Lighthill acoustic analogy by comparison with DNS results for a three-dimensional, turbulent flow. To the author's knowledge, no such validation has previously been accomplished. In the DNS, both the turbulence and the acoustics in the far field are computed by solving the three-dimensional, compressible, unsteady Navier-Stokes equations. Boundary conditions are periodic in the x- and z-directions and nonreflecting in the y-direction. Acoustic wave propagation is statistically one-dimensional; the plane-mean sound propagates from the turbulence to the acoustic fax field in the y-direction. Analysis predicts that the plane-mean sound is equivalent to sound radiated by a distribution of dipole sources; the amplitude and frequency of plane-mean density fluctuations in the acoustic far field are predicted to scale as M3t and Mt , respectively, for a range of frequencies. DNS results confirm the acoustic-analogy predictions. This study is perhaps the first successful attempt to validate the Lighthill acoustic analogy for sound radiated from a three-dimensional, turbulent flow by comparison of DNS results with acoustic-analogy predictions.