When an axisymmetric underexpanded jet impinges on a flat plate perpendicularly, the feedback loop of the sound waves in and around the jet is known to cause the oscillation of the whole flow field. In this paper, the radial underexpanded jet issuing from a slit nozzle which consists of two tubes, face to face each other, is studied experimentally and numerically. Such flow field can be considered as a simple model of the wall jet of the impinging jet on the plate. In the experimental photograph, it is found that some shock rings appear around the nozzle and that the distortion and the deformation of the rings occur. They are considered to be caused by the sinusoidal oscillation of the jet and the motion of the vortices around the jet. Such oscillatory phenomena are shown by the computational results. Furthermore, the feedback mechanism of the readial jet is also discussed under the assumption of the axisymmetric flow field.

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