An experimental investigation into the influence of installed passively controlled jet flows on wall-pressure fluctuations

Jet-surface interaction(JSI) represents a significant noise problem in the installation of modern ultra-high bypass ratio turbofan engines. The use of chevron nozzles is known to reduce low-frequency jet mixing noise(JM) by increasing the velocity gradient in the jet shear layer. This effect is expected to influence the jet flow in the vicinity of the wing and to modify the jet-surface interaction noise. To clarify the physics of these two(JSI and JM) noise source mechanisms, an extensive experimental investigation has been conducted in the anechoic chamber of the Doak Laboratory at the University of Southampton. Various measurements were carried out on an isolated subsonic jet and an installed beneath a 2D NACA4415 airfoil using different nozzle shapes and passive vortex generator geometries. The wall-pressure field on the airfoil surface was investigated using a set of wall-pressure transducers flush-mounted in the streamwise and spanwise directions on the pressure side of the airfoil. The unsteady wall-pressure data were analysed in both time and frequency domains to assess changes in: 1) surface trailing edge spanwise correlation length, 2) streamwise convection velocity of the hydrodynamic pressure field, and 3) modification of the hydrodynamic pressure field in the vicinity of the surface trailing edge.