Jet-Airframe Interactions for Noise Suppression
The Embry-Riddle team developed a passive noise suppression technology utilizing the interactions of the airframe with the jet plume. In this technology, the flat surface of the airframe adjacent to the jet plume is modified to create a slightly wavy surface instead. Such design modification can be applied to the existing design concepts with engine mounted under the wing, as well as, the top-mounted engine configurations. The near-field perturbations are reflected by the wavy surface to create an excitation wave to amplify the jet and the shear layer instability. The wavy-surface parameters are designed such that the excitation frequency is the harmonic of the fundamental frequency responsible for the peak noise. Through nonlinear fundamental-subharmonic interaction, the sound source and its radiated far-field noise are reduced. To verify this concept, high-fidelity simulations of a supersonic rectangular jet in the vicinity of the airframe surface were carried out. Results show that when the flat airframe surface is reduced by a wavy one, the radiated sound was reduced by 3.7dB for top-mounted engine, and by 2.6dB for under-airframe engine.