Experimental Study on Flow Transition in Dual Bell Nozzles

The dual bell nozzle is a concept of altitude adaptive nozzles. The flow adapts to the altitude by separating at the wall inflection at low altitude, and flowing full at high altitude. To understand the phenomenology of the flow by the transition from sea level to high altitude mode, a series of tests have been made under subscale cold flow conditions. Three nozzles with different geometries have been tested. Two of them were successively shortened and driven under the same conditions for each extension length. This study yields the influence of the geometric parameters of the base and extension on the transition conditions. Furthermore a prediction of the transition conditions is given.