Performance of a hypersonic twin-nozzle system

A numerical investigation of a planar twin-nozzle system is made on the basis of previous experimental and numerical studies that indicated that the performance of single expansion ramp nozzles, suitable for the propulsion of any type of hypersonic cruise vehicle, can possibly be improved by the application of a bypass jet and gas injection at the ramp. The assumption of planar flow is justified by the flow properties in the near-field of a jet issued from a large-aspect-ratio slit nozzle. Systematic variations of the stagnation state and the dimensions of the secondary nozzle are performed and indicate that a good control of the primary jet channel shaping—and therefore also of the pressure distribution along the ramp contour—can be achieved by using a cold secondary jet that then acts as a kind of gaseous wall. The mass flux of the secondary jet must be of the order of the primary jet flux to obtain a satisfactory shaping effect over a sufficiently large distance. For far off-design cases, however, overexpansion of the primary nozzle jet still will result in flow recompression by shock waves and flow separation in downstream regions of the ramp contour. It is shown that wall bleeding in small sections of the wall is one possibility to influence and to stabilize the thrust vector control.