Coherent Structures Producing Machwaves Inside and Outside of the Supersonic Jet

Summary

Supersonic jets emit Machwaves which are rather regular ones. Previous investigations using visualizations and an optical microphone have revealed that these Machwaves are shock waves which are accompanying mixing layer structures travelling downstream at three preferred speeds. The experimental results could be approximated by very simple relations. Local measurements within the mixing layer are needed in order to find out the reason for these relations. Two particular doppler velocimeters have been used for doing such measurements. They have shown that a weak regular contribution to the essentielly random velocity fluctuations exists. All results obtained so far agree with a hypothesis which is based upon the idea that the regular contribution consists of a vortex pattern the movement and extent of which are governed by pressure waves.