Noise Reduction Performance of Aerodynamic Tabs in a Supersonic Jet

Abstract

Noise reduction performance of aerodynamic tabs in an under-expanded supersonic jet is investigated experimentally. From a converging round nozzle, air is injected into the atmosphere (Main jet) at a pressure ratio of 2.25 (Mj=1.14). The nozzle exit diameter D=8.0mm. From small nozzles mounted in the main jet nozzle wall, air is injected in the normal direction to the main jet (Secondary jet). The nozzle exit diameter d=1/8D and 1/16D, and the number of nozzles is varied from 1 to 8. The average total pressure of the main jet decreases with the increase in the total mass flow rate of the secondary jets. The secondary jet penetration is estimated from the momentum flux ratio and the secondary jet nozzle exit diameter. Equivalent secondary jet penetration is introduced to consider the effect of the number of secondary jet nozzles. The screech SPL decreases monotonously with the increase in the equivalent secondary jet penetration. The OASPL, which represents the broadband noise level, also decreases with the increase in the equivalent secondary jet penetration, and takes the minimum value where the screech is removed.It i§ shown that the jet penetration is one of the most important criteria of the noise reduction performance of aerodynamic tabs.