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LDA MEASUREMENTS IN HIGH MACH NUMBER AXISYMMETRIC JET SHEAR LAYERS

Tong Feng
Dept. Of Aero. and Auto. Eng., Loughborough University, Loughborough, Leicestershire LE11 3TU, UK

James J. McGuirk
Department of Aeronautical and Automotive Engineering, Loughborough University, Leicestershire, United Kingdom

Abstract

An experimental survey has been undertaken to understand the behaviour of the annular mixing layer in the initial near-field region of axisymmetric jet development. High Mach number jets issuing from a convergent nozzle at Nozzle Pressure Ratios (NPR) from 1.68 to 3.0 were measured using LDA instrumentation. Detailed radial profile data are reported, particularly within the potential core region for mean velocity, turbulence rms and turbulent shear stress. Significant effects of NPR for supercritical jets were observed in the inviscid shock cell region, but profiles in the shear layer collapsed remarkably well. The growth rate of the annular shear layer over the potential core length was evaluated for a range of NPRs including underexpanded cases. A comparison of the compressibility-induced reduction in shear layer growth rate with planar shear layer data showed notable differences, with compressibility effects beginning earlier and being stronger than for planar shear layers.