Intensity, scale and convection of turbulent density fluctuations

Abstract

This paper extends the quantitative schlieren technique to the separate determination of the local scales and intensity of turbulent density fluctuations. Measurements in an unheated supersonic jet are also extended to positions substantially further away from the jet than those reported hitherto, and show that high levels close to the nozzle reduce to levels comparable to subsonic velocity fluctuations beyond 18 diameters from the nozzle exit. Trends for the integral scales are similar to those based on subsonic jet velocity fluctuations. Separated-beam measurements show reflexion of disturbances on the jet centre-line just beyond the potential core. Spectra show a more peaked form close to the jet, and exhibit a rapid decrease in level with wavenumber.