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Turbulence and Shear Flow Phenomena -1 First International Symposium

ISBN Imprimir: 1-56700-135-1

EXPERIMENTAL STUDY OF ANNULAR SUPERSONIC MIXING LAYERS: TURBULENT KINETIC ENERGY BUDGET

Resumo

This paper presents turbulence measurements using Laser Doppler Velocimetry (LDV) in an annular supersonic mixing layer. The experimental apparatus consists in a circular supersonic jet (Dj = 50mm; Mj = 2.5) issuing in a subsonic flow (M~0.2). This situation generates an annular supersonic mixing layer in which convective Mach number is close to 0.9 making possible the observation of quite strong compressibility effects. Mean and turbulent velocity fields were then obtained using 3500 to 4000 samples at each experimental point. This high number of data ensures a good statistical convergence and accuracy for LDV measurements. Mean velocity fields exhibit the usual behavior of a compressible mixing layer. The spreading rate collapses well with plane mixing layers values obtained at the same convective Mach number. The Reynolds stress tensor is also similar to the one obtained in plane mixing layer case. Then, it seems that no crucial difference exists between plane and annular flow cases when dealing with mean velocity fields and Reynolds stress tensor. Using Strong Reynolds Analogy assumptions to estimate velocity-density correlations from LDV measurements it was then possible to compute turbulent kinetic energy budget. This budget seems to be very similar to the one obtained in a compressible plane mixing layer. The present results were also compared to DNS results in the same kind of flow. Some quantitative difference between the experimental and the computed budget are observed, but a good qualitative agreement is obtained. Particularly, the dissymetry of the diffusion term is confirmed both by experiments and computations in this kind of annular flow configuration.
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