Turbulence Measurements Relevant to Jet Noise

Abstract

Two-point space-time correlations of both the turbulent velocities and the square of these velocities have been measured in the mixing region of a 4-in. low-speed model jet (about 140 fps) with constant temperature hot-wire anemometers. These measurements include the ordinary u component of the turbulent velocity and also the components at 45° and 60° to the jet axis. Using the moving axis transformations of these space-time correlation functions together with the mean velocity measurements, an attempt has been made to estimate the basic directivity, the intensity, and the spectrum of both the “shear” and the “self”-noise generated by a unit volume of jet turbulence. The calculations are based on the Proudman form of Lighthill's integral for aerodynamic noise and Ribner's notion of “shear” and “self”-noise. The present attempt entails more experimental precision and is more advanced than previous work: very few generalizations and assumptions have been made concerning the complex velocity correlations that constitute the integrand of Lighthill's integral.