Micro-shock waves generated inside a fluid jet impinging on plane wall

An Nd:glass laser pulse (18 ns, 1.38 J) is focused in a tiny area of about 100-mum diam under ambient conditions to produce micro-shock waves. The las er is focused above a planar surface with a typical standoff distance of ab out 4 mm, The laser energy is focused inside a supersonic circular jet of c arbon dioxide gas produced by a nozzle with internal diameter of 2.9 mm and external diameter of 8 mm, Nominal value of the Mach number of the jet is around 2 with the corresponding pressure ratio of 7.5 (stagnation pressure/ static pressure at the exit of the nozzle), The interaction process of the micro-shock wave generated inside the supersonic jet with the plane wall is investigated using double-pulse holographic interferometry. A strong surfa ce vortex field with subsequent generation of a side jet propagating outwar d along the plane wail is observed. The interaction of the micro-shock wave with the cellular structure of the supersonic jet does not seem to influen ce the near surface features of the flowfield. The development of the coher ent structures near the nozzle exit due to the upstream propagation of pres sure waves seems to be affected by the outward propagating micro-shock wave . Mach reflection is observed when the micro-shock wave interacts with the plane wall at a standoff distance of 4 mm, The Mach stem is slightly deflec ted, indicating strong boundary-layer and viscous effects near the wall. Th e interaction process is also simulated numerically using an axisymmetric t ransient laminar Navier-Stokes solver. Qualitative agreement between experi mental and numerical results is good.