Abstract
Broadband root-mean-square (rms) values and frequency spectra for pressure fluctuations in the supersonic boundary layer on a Mach 3 DeLaval nozzle sidewall and in the freestream are reported for both adiabatic and cooled surface conditions. The flat sidewall of the nozzle contained four sections independently cooled by liquid nitrogen. During the experiments, the flat sidewall was operated (1) adiabatically, (2) cooled in an approximately uniform manner to −40°C, and (3) cooled in a nonuniform manner. For all thermal boundary conditions on the sidewall, a dynamic pitot probe was traversed through the boundary layer and into the freestream to measure the broadband pressure fluctuations from 30 Hz to 100 kHz. The influence of sidewall cooling on the measured pressure fluctuations was dependent on the unit Reynolds number. Compared with the pressure fluctuations measured with an adiabatic sidewall, uniform cooling of the sidewall was found to reduce the rms pressure fluctuations in both the boundary layer and the freestream by approximately 50% at the highest stagnation pressures used (unit Reynolds numbers above 44,000/cm). Uniform cooling of the sidewall increased rms pressure fluctuations for lower stagnation pressures (unit Reynolds numbers below 44,000/cm). A reduction in the pressure fluctuation amplitude within the boundary layer resulted in a corresponding reduction in the pressure fluctuation amplitude in the test section freestream. Tests using a nonuniform temperature distribution on the sidewall indicated that cooling the portion of the sidewall covering the nozzle throat had the most influence on the pressure fluctuations in the boundary layer and in the freestream.
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Acknowledgments
The reported work was partially supported by the State of Montana (USA) under the 1999 MONTS/EES Research Program as contract 414518. Undergraduate Research Assistant Thomas Nickou created the detailed drawings of the liquid cooled sidewall using the Pro-Engineer drawing and solids modeling program. Mr Nickou also processed many of the measured temperature distributions on the cooled sidewall to suitable graphical representations. Undergraduate Research Assistant Russell Stuver designed the system of piping and valves to supply liquid nitrogen to the cooled sidewall. Mr Stuver also performed a majority of the data processing. Technicians David Cox, Pat Vowell, and Kevin Amende skillfully machined the cooled sidewall from solid aluminum alloy plate. Dr. A. Demetriades assisted with writing the successful proposal on which the work was based, provided technical advice early in the project, and designed an improved mount for the DPP which functioned perfectly throughout the sequence of experiments.
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George, A.H., Amin, M.R. The influence of sidewall cooling on boundary layer pressure fluctuations for a two-dimensional supersonic nozzle. Exp Fluids 35, 58–69 (2003). https://doi.org/10.1007/s00348-003-0635-8
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DOI: https://doi.org/10.1007/s00348-003-0635-8