Experimental investigation of the inflection geometry on dual bell nozzle flow behavior

The altitude adaption of the dual bell nozzle is achieved by the contour inflection, leading to a symmetrical and controlled separation under sea level conditions. When reaching a certain pressure ratio, the transition to high altitude mode takes place and the nozzle flows full. Former experimental studies have shown the existence of an intermediate flow state before the transition from one operating mode to the other takes place: the sneak transition, characterized by the separation of the flow downstream to the inflection, leading to increased side loads. To minimize this effect, various contour inflection geometries have been investigated. The study was divided into a cold flow and a warm flow test campaign on sub-scale planar models.