This research activity deals with the interaction of the wake and jet flow of a generic space launcher equipped with an altitude compensating nozzle. Altitude compensating nozzles offer the advantage of increased thrust compared to conventional used nozzles. One realization of an altitude compensating nozzle is the dual-bell nozzle which features a one step altitude compensation. This is achieved by a contour inflection dividing the nozzle in two parts, the base nozzle and the nozzle extension. The nozzle flow separates at the contour inflection at low altitudes where the ambient pressure is high. The nozzle is then in sea-level operation mode. With increasing altitude of the launcher and thus decreasing ambient pressure, the nozzle switches to altitude mode with an attached nozzle flow throughout the whole nozzle what increases the thrust. Despite the advantages the dual-bell nozzle offers, it was not jet tested in flight since the transition process from sea-level mode to altitude mode has been a severe uncertainty in the design. High side loads can be generated if the flow separation is unsymmetrical what may destroy the nozzle. Especially, the interaction of an outer flow and the nozzle transition is still largely unknown. This research activity therefore investigates the interaction of a supersonic outer flow and the nozzle flow. It is observed, that in the presence of a supersonic outer flow an alternating switch between sea-level and altitude mode occurs for certain geometric configurations and nozzle total pressures. This nozzle operation behavior is known as flip-flop mode and should be avoided since it is very detrimental for the nozzle structure. The research approaches of this project are the following:
This research activity is founded by the German Research Foundation (Deutsche Forschungsgemeinschaft - DFG) in the framework of the Sonderforschungsbereich Transregio 40.
Alexander Barklage