Supersonic flow separation in planar nozzles |
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Authors: | Dimitri Papamoschou Andreas Zill Andrew Johnson |
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Institution: | (1) University of California, Irvine, CA, USA;(2) Pankl Aerospace Systems, Cerritos, CA, USA |
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Abstract: | We present experimental results on separation of supersonic flow inside a convergent–divergent (CD) nozzle. The study is motivated
by the occurrence of mixing enhancement outside CD nozzles operated at low pressure ratio. A novel apparatus allows investigation
of many nozzle geometries with large optical access and measurement of wall and centerline pressures. The nozzle area ratio
ranged from 1.0 to 1.6 and the pressure ratio ranged from 1.2 to 1.8. At the low end of these ranges, the shock is nearly
straight. As the area ratio and pressure ratio increase, the shock acquires two lambda feet. Towards the high end of the ranges,
one lambda foot is consistently larger than the other and flow separation occurs asymmetrically. Downstream of the shock,
flow accelerates to supersonic speed and then recompresses. The shock is unsteady, however, there is no evidence of resonant
tones. The separation shear layer on the side of the large lambda foot exhibits intense instability that grows into large
eddies near the nozzle exit. Time-resolved wall pressure measurements indicate that the shock oscillates in a piston-like
manner and most of the energy of the oscillations is at low frequency.
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Keywords: | Supersonic nozzle flow separation Oscillating shock Flow instability |
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