Experimental and Numerical Study of Dual Bell Nozzle Flow

Kurzfassung

The dual bell is a nozzle concept for altitude adaption. The flow separates at the contour inflection in sea level mode in a mainly controlled and symmetrical way, reducing the side load generation and increasing the thrust. The transition to altitude mode is reached when the flow suddenly attaches to the extension for an improved altitude thrust. The conditions of this transition and its evolution are the key for the study of dual bell nozzles. For a better understanding of the flow behavior, a 2D subscale dual bell model has been designed and tested at the German Aerospace Center (DLR). The tests were divided into two campaigns and performed under cold and warm flow conditions. The evolution of the shock system at the inflection during the transition was observed using schlieren optics. The planar nozzle was tested under various conditions in pressure and temperature. Both test campaigns have been recalculated in cooperation with Astrium. Numerical and experimental results are presented in this paper.