The oscillatory response of multiple shock waves to upstream disturbances in a supersonic flow is studied numerically in a constant area rectangular duct. The flow is accelerated through a nozzle with an exit Mach number of 1.75 and continues in the constant area duct, where multiple shock waves are formed. To investigate the effect of upstream disturbance on shock oscillations, three parameters are varied systematically: upstream turbulent intensity, frequency of upstream pressure fluctuation, and amplitude of upstream pressure fluctuation. The wall shear stress variation along the duct length provides the location of separation and reattachment points in the flow field. The wall pressure frequency spectra were used to investigate the low-frequency unsteadiness in shock oscillations. The power spectral density of the wall static pressure and the probability density function (PDF) of shock location are analyzed, and the results suggest that as the upstream turbulent intensity is increased, the dominant frequency of oscillation is increased and the shock oscillations become more symmetrical. As the upstream disturbance frequency is increased, the shock oscillations become more symmetrical and follow the Gaussian curve closely. The shock wave oscillates with the same upstream excitation frequency when the upstream disturbance amplitude is increased. At large values of upstream disturbance amplitude, the PDF shows a large deviation from the Gaussian, and the rms amplitude of shock oscillation increases monotonously. At higher amplitudes of upstream disturbance excitation, the traces of shock train leading-edge location display path-dependence characteristics.
A fixed-geometry diffuser system was tested in an arc-heated, hypersonic, open-jet wind tunnel. facility at Mach numbers between 14 and 18 and Reynolds numbers (based on nozzle exit diameter) between 8,900 and 25,000. Tests were conducted both with an empty test section and with conical models in the flow. Test variables included test section open-jet length, diffuser second-throat length, and diffuser inlet geometry. Diffuser efficiency improved with increased diffuser secondthroat length, with increasing Reynolds number, and with the addition of conical models into the flow. Changes in open-jet length and diffuser inlet geometry had no appreciable effect on diffuser efficiency with an empty test section. A streamlined model support strut produced marked improvement in diffuser efficiency over a blunt support strut. I
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