Measured Velocity Fluctuations Inside the Mixing Layer of a Supersonic Jet

Summary

The supersonic jet emits Machwaves which are rather regular ones, Previous experiments have shown that they are shock waves accompanying more or less circumferential mixing layer structures which are travelling at three preferred speeds. In order to find out the nature of these structures two special Doppler velocim-eters have been used for continuously recording the flow velocity fluctuations inside the mixing layer of a Mach-2-jet. In general the results agree with those obtained by many authors using hot wires or sampling Doppler velocimeters at lower Mach-numbers. No indication at all has been found however on the existence of a regular vortex pattern producing the shock waves. But in the present case the three preferred speeds were found to be the convection velocities in the middle and at the two edges of the mixing layer. The difference between those at the edges as well as the highest flow velocity variation within a certain layer equalled the sound speed.