Revisiting Compressibility Effects in Free Shear Layers Using Advanced Optical Diagnostics

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ABSTRACTPROPOSAL NO.: CTS-0306266PRINCIPAL INVESTIGATORS: MOHAMMAD SAMIMYINSTITUTION: OHIO STATE UNIVERSITY REVISITING COMPRESSIBILITY EFFECTS IN FREE SHEAR LAYERS USING ADVANCED OPTICAL DIAGNOSTICSCompressible jets are utilized in a myriad of engineering applications, vary in size from one millimeter in passenger size automobile fuel injectors to one meter in commercial airplane jet engines, and are almost always high Reynolds number and turbulent. In a recent work conducted by this team, a novel MHz rate planar imaging system was used to generate real-time movies of large-scale structures within supersonic axisymmetric jets. A key result was that for relatively high compressibility level (convective Mach number of 0.87), the convective velocity exhibited a bimodal distribution where structures were either approximately 33% faster or slower than theory predicted. Such deviation from theory has been found previously in planar shear layers, but has never been observed to deviate with both a fast and a slow mode in the same flow. A comprehensive study will systematically explore the effects of a matrix of variables such as flow geometry, flow visualization method, and compressibility level, on the dynamics of turbulence structures and their measured convective velocity. The work will advance "discovery and understanding" by involvement of graduate and undergraduate students, incorporation of the measurement techniques developed into the graduate curriculum, and rapidly disseminating the principal findings by maintaining an active web site and by participation of students and PIs in national and international meetings.