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PIV And Schlieren Measurements Of A Linear Plug Nozzle Jet Interacting With External Flow

Paul Wißmann, Christian J. Kähler, Sven Scharnowski

University of the Bundeswehr Munich, Neubiberg, Germany


Plug nozzles represent a promising concept as part of a propulsion system for space launchers. The ability to adapt the nozzle jet to the ambient pressure level improves thrust performance in overexpanded operating conditions compared to conventional bell nozzles. In this study, the dynamics of a jet flow of a cold air plug nozzle model are investigated by means of PIV and high-speed schlieren measurements. For a fixed nozzle pressure ratio, the jet flow is studied in an externalouter flow environment with sub-, trans-, and supersonic Mach numbers. The effect of plug truncation is analyzed as well. It is found that the outer Mach number strongly influences the flow pattern, local velocity magnitudes and aerodynamic modes. The frequency and dominance of vortex shedding and jet screeching modes are found to be highly dependent on the Mach number of the surrounding flow. A truncated plug introduces local accelerations in its base wake region, causing an increased shock strength in the jet structure. In addition,it causes severe periodic fluctuations in the flow that are transmitted to the shear layer and induce acoustic wave emissions. The impact of the plug length on the flow dynamics has been seen to decrease with increasing outer Mach number.

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