An experimental and theoretical study of the interaction between an underexpanded rarefied jet and a perpendicular plane obstacle

A classification is proposed for flow regimes in front of an obstacle during the transition of continuous flow to free molecular flow. The boundaries of the various flow regimes are determined quantitatively as a function of the Reynolds number derived from flow parameters in the critical section of the nozzle and the distance to the obstacle. It is shown experimentally that an increase in the degree of rarefaction can shift the boundaries of the flow types typical of dense jets. It is also shown that an increase in the degree of rarefaction in the shock layer can cause the disappearance of the central circulation region.