Boundary-layer separation in supersonic propelling nozzles

Abstract

A comparison has been made between the pressure rise at separation in convergent-divergent nozzles and that in other models with supersonic flow and a turbulent boundary layer. In the case of nozzles with uniform divergence, close similarity is found to the characteristics of separation induced on surfaces with initially zero pressure gradient. Where exceptions to this general agreement occur, three special categories of nozzle data can be distinguished. The first, involving a change of behaviour in the vicinity of separation, is attributable to the existence of a laminar boundary layer or of one in a state of transition. A critical value of Reynolds number at separation, based on equivalent flat-plate length, is found to be around 0.7 million. The second form of abnormality corresponds to an unusually large amount of pressure rise in the region between separation and nozzle outlet; this can occur in nozzles of low divergence angle with either turbulent or laminar separation, the effect being most pronounced with the latter. Third comes the case of a shock.system in close proximity to nozzle outlet, where the full interaction pressure rise with a turbulent boundary layer is unable to develop.