Numerical simulation of different separated flow structures in supersonic nozzles

Two different separated flow structures may take place in supersonic rocket nozzles: the first is characterized by the classical separation at wall (free shock separation), whereas the second features a small separated region followed by reattachment and a large recirculating region at the nozzle core (restricted shock separation). The existence of these two structures is of great practical interest because it seems to provide a reasonable explanation for the generation of high side load peaks during startup transients, and because it seems to take place only in some families of nozzles. In the present paper flow separation in supersonic rocket nozzles is studied numerically to analyze the reasons leading to the generation of the different structures and to discuss problems concerning their numerical simulation.