Mach Number Effect on Aeroacoustic Characteristics of Compressible Jet Due to Chevron

The present experimental investigation reports the effect of chevron on flow characteristics and associated acoustic characteristics at different jet exit Mach numbers in high subsonic compressible jet. Flow characteristics are investigated with mean pressure measurement using miniature pitot tube in the flow, and acoustic characteristics are investigated using fluctuating pressure measurement with array of four microphones in the far field of jet. Chevron is used as a flow control device on the lip of the nozzle. Chevron converts axisymmetric jet development into corrugated shear layer, closer to the nozzle exit. This effect diminishes as jet grows downstream away from the nozzle exit. Corrugation of jet shear layer closer to the nozzle exit increases with increase in Mach number. Compressibility effect with change in Mach number is seen from potential core length and jet growth rate for base nozzle; however, chevron is found to reduce the compressibility effect with change in jet exit Mach number due to enhancement in mixing. Chevron reduces far-field overall sound pressure level at shallow polar angle (30°) by about to 2 dB at all the Mach number; however, increase in noise level at higher frequency observed at higher polar angle is mainly due to high-frequency noise sources produced from chevron petals. Noise level at higher polar angles and higher frequencies increases with increase in Mach number.