Flow separation modes and side phenomena in an overexpanded nozzle

As a part of an aerodynamics Ecole Polytechnique project, separation modes which occur in supersonic nozzles at overexpanded regimes are numerically investigated and compared with known effects. Different shock generation and reflections in different nozzle types are observed and their impact on the two main separation modes, namely Free and Restricted Shock Separation (FSS & RSS) is explored. ONERA' experimental thustoptimized-contour (TOC) rocket nozzle was the reference case and it is compared with the corresponding Vulcain 2 nozzle and analogues conical and TIC nozzle contours. Strong lateral forces and side effects on the nozzle wall caused by the RSS and by transition FSS to RSS are depicted in terms of flow unsteadiness and presented in flow charts and diagrams. Additionally, some design criteria for modern thrust optimized nozzles according to these effects are proposed