Pitot pressures of correctly-expanded and underexpanded free jets from axisymmetric supersonic nozzles

The structures of the axisymmetric free jets from supersonic nozzles with the exit Mach numbers of 1.5 and 2.0 are studied with special attention to the decay of the Pitot pressures downstream of the Mach disk. The Pitot pressure probe and schlieren method are used in the experiments to diagnose the flowfield. A TVD numerical method is also applied to the Euler equations, and the computed jet structures are compared with experiments. In the underexpanded jet, the experimentally obtained Pitot pressure near the jet centerline is found to substantially recover downstream of the Mach disk. By comparing the numerical computation, this phenomenon is thought to be caused by the turbulent momentum transfer to the central region from the region outside the slip line where the stagnation pressure loss is small.