Experimental Investigation of Screech-Tone Characteristics of Jet Interaction with a Flat Plate

The screech-tone characteristics of an underexpanded jet in the vicinity of a flat plate in which the jet is emitted from a circular sonic nozzle and interacts with a flat plate placed parallel to the jet axis, have been investigated experimentally. The flow is visualized using the schlieren technique, and the unsteady pressure on the flat plate as well as the sound pressure level in the far field are measured for different jet-plate separation distances. It is found that screech tone vanishes when the flat plate comes close to the jet axis. However, there is an azimuthal directivity in its propagation, which depends on jet-plate separation distance. In addition, the highly oscillating baseline jet flow is suppressed by the jet-plate interaction, and screech tone completely disappears when the jet-plate separation distance becomes less than 0.61 of the jet diameter.