POD Analysis of Sound Generation by a Turbulent Jet

A Proper Orthogonal Decomposition (POD) is constructed for a Mach 0.9 turbulent jet using a well-validated direct numerical simulation database. Norms are defined based on near-field volume integrals of pressure, turbulence kinetic energy, streamwise velocity, and total enthalpy, two-dimensional integrals of streamswise velocity (to match experimental measurements), and far-field integrals of pressure over a sphere. We find substantially different POD modes for the different norms, and their efficiency at representing the full data is strongly dependent upon the norm and specifically which data we attempt to represent. To reproduce near-field turbulence statistics requires relatively few modes computed by a kinetic energy or pressure norm. However, a large number of the POD modes computed using a near-field norm are required to represent the sound field. The dominant near-field POD modes computed with either the near-field pressure norm or the sound field norm have the structure of wave packets

Measurements of the turbulent energy dissipation rate

The one-dimensional surrogate for the dimensionless energy dissipation rate C/sub epsilon / is measured in shear flows over a range of the Taylor microscale Reynolds number R/sub lambda /, 70or approximately=300, a value of C/sub epsilon / approximately=0.5 appears to be a good universal approximation for flow regions free of strong mean shear. The present results for C/sub epsilon / support a key assumption of turbulence-the mean turbulent energy dissipation rate is finite in the limit of zero viscosit