Measurements of two-point velocity correlations in a round jet with application to jet noise

Abstract

This work documents two-point space-time correlation measurements made in a cold, M=OS round jet using a pair of two-component hotwire probes, From the simultaneously measured velocities space-time correlations are computed for axial and radial displacements for several radial locations each at three axial stations (4, 8, and 20 diameters). This rich type of turbulence data is required in many jet noise prediction theories, such as the Mani-Gliebe-Balsa (MGB) theory. In the past, these terms have been estimated from an isotropic, homogeneous turbulence model with a Gaussian form for space and time dependence. This turbulence model resulted in a particular partitioning of turbulent kinetic energy among the many quadrupole components. The work presented here indicates that such models are in error and proposes an axisymmetric model with lower order exponent. This model results in a different ratio of source directivities, which will impact the predicted jet noise source directivity. Using a lower-order exponent in the time-dependent part of the space-time correlation also shows better agreement with data and will change the predicted jet noise spectral characteristics.