Flap contour optimization for highly integrated SERN nozzles

The performance of a Single Expansion Ramp Nozzle (SERN) for hypersonic cru ise vehicles is examined with focus on the flow at the nozzle flap and the corresponding separation of the boundary layer. Two wind tunnel models are used to analyze the interaction of the free stream and the nozzle flow and the flow at the flap in detail. A finite element how code is employed to su pport the design of the Bap model and the analysis of the flow. Comparative contour studies show that the size and the location of the sepa ration at the flap cowl and therefore the aerodynamic quality can be influe nced by optimizing the flap cowl contour. The position of the separation is measured for different contours and varying Reynolds numbers at laminar, t ransitional and turbulent flow conditions. Numerical studies of a nozzle/af terbody configuration suggest an improvement of up to 3.5% in axial thrust for optimized flap contours in the examined Mach range between 1.64 and 6. At the same time the rotation of the thrust vector is reduced by up to 5 de grees at lower Mach numbers. (C) 2000 Editions scientifiques et medicales E lsevier SAS.