Supersonic Jet Noise Reduction by Coaxial Jets with Coplanar and Staggered Exits

Abstract

Far-field noise radiated from coaxial cold underexpanded jet flows issuing from convergent two-nozzle configurations with coplanar and staggered-exits is investigated experimentally. The coaxial jets are operated in the "inverted" mode, i.e., the outer (annular) jet flow Mach number is higher than that of the inner (round) jet. Keeping all other geometrical and operating conditions the same, the exit-stagger of the inner (round) and the outer (annular) nozzles was varied. It is shown that the extent of the exit-stagger affects both the flows and the radiated noise from such coaxial underexpanded jet flows and that comparatively, the lowest noise levels are achieved when the coaxial nozzle-exits are coplanar. Moreover, the effectiveness of the co-flowing inner jet flow in reducing the noise radiated from either the annular or the coaxial underexpanded jet flows decreases noticeably as the exit-stagger is increased.

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