Noise Reduction of a Supersonic Jet Using Gas Injection from a Nozzle Wall

Abstract

Effects of gas injection from a nozzle wall on screech reduction of a supersonic under expanded jet are investigated experimentally. From a converging round nozzle, air is injected into the atmosphere (Main jet) at a pressure ratio of 2.25 (M =1.14). The exit diameter of the main jet nozzle is 8.0 mm. From small nozzles mounted in the main jet nozzle wall, air is injected in the normal direction to the main jet (Secondary jet). The exit diameter of the secondary nozzles is 1.0 mm. The number of the secondary nozzles is selected to be 2 or 4, and the mass flow rate of each secondary jet is set at 2.0% or 4.0% of the main jet. With the secondary jets, the screech SPL is reduced by 23 dB at the maximum, and the frequency profile of the broadband noise is also influenced. And with the secondary jets, the total pressure of the main jet is slightly decreased with the increase in the total mass flow rate of the secondary jets. Consequently, it is shown that the gas injection method is effective in screech reduction with a small loss in the total pressure.