Jet-plate interaction in a supersonic screeching jet

This work presents an experimental investigation of the effect of a flat plate on the generation of axisymmetric A1 and A2 screech modes. The plate is installed parallel to the nozzle axis of an under-expanded supersonic jet issuing from a convergent nozzle at a radial distance of 0.7 nozzle diameters from the nozzle axis. The impact of the plate on the screech generation is assessed via acoustic measurements in the far field of the jet. We show that the surface presence drastically modifies the usual staging between A1 and A2 modes. Specifically, the plate induces the disappearance of the A2 mode and an extension of the A1 mode to the jet flow conditions for which A2 mode is usually supported in the free-jet case. Schlieren measurements are carried out to assess whether the modifications of the screech mode appearance might be related to modifications of the shock-cell structure within the jet.