Shock-Generated Vortices in Rocket Nozzles

During the engine startup and shutdown of space launchers the nozzles operate in overexpanded regime, and flow separations in the divergent section may take place; their asymmetric character can yield side loads on the nozzle wall, with consequent major structural problems. These phenomena may also occur during the flight because of the buffeting effects caused by the recirculating flow at the launcher base. The study illustrates the basic characteristics of the phenomena inside the nozzle divergent section, and the physical origin of the side loads in classical nozzle configurations. The possible generation of the “inviscid separation phenomenon”, and its role on the occurrence of regimes of free- and restricted-shock separation are discussed. Moreover, a semi-analytical model is developed, to predict the shock shape and the possible vortex generation behind it.