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Fluorescence Imaging Study of Transition in Underexpanded Free Jets

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3 Author(s)
Wilkes, J.A. ; Department of Physics, The College of William and Mary, Williamsburg VA 23187 USA and NASA Langley Research Center, Hampton VA, 23681-2199. email address: jennifer.a.wilkes@nasa.gov ; Danehy, P.M. ; Nowak, R.J.

Planar laser-induced fluorescence (PLIF) is demonstrated to be a valuable tool for studying the onset of transition to turbulence. For this study, we have used PLIF of nitric oxide (NO) to image underexpanded axisymmetric free jets issuing into a low-pressure chamber through a smooth converging nozzle with a sonic orifice. Flows were studied over a range of Reynolds numbers and nozzle-exit-to-ambient pressure ratios with the aim of empirically determining criteria governing the onset of turbulence. We have developed an image processing technique, involving calculation of the standard deviation of the intensity in PLIF images, in order to aid in the identification of turbulence. We have used the resulting images to identify laminar, transitional and turbulent flow regimes. Jet scaling parameters were used to define a rescaled Reynolds number that incorporates the influence of a varying pressure ratio. An empirical correlation was found between transition length and this rescaled Reynolds number for highly underexpanded jets.

Published in:

Instrumentation in Aerospace Simulation Facilities, 2005. iciasf '05. 21st International Congress on

Date of Conference:

2005