Turbulent Prandtl number and spectral characteristics of a turbulent mixing layer

Abstract

Measurements have been made of all three velocity fluctuations and of the temperature fluctuations in a thermal mixing layer associated with a turbulent plane jet. In a region of the flow for which the Reynolds stresses and heat fluxes are large, the turbulent Prandtl number is equal to about 0.4. The small magnitude of the turbulent Prandtl number in the present and other mixing layer investigations seems to reflect the relatively strong coherence of the flow. Spectra and cross spectra of velocity and temperature fluctuations exhibit a pronounced peak at the average frequency of the coherent motion. A close similarity is noted between the spectrum of the lateral velocity fluctuation and the temperature spectrum.