Numerical simulation of supersonic jet noise

Abstract : Jets with complex shock-cell structures appear in numerous technological applications. Most supersonic jets used in aeronautics will be imperfectly expanded in flight, even those from carefully designed convergent-divergent nozzles. The adaption to the ambient pressure takes place in a sequence of oblique shocks which interact with the free shear layers and produce noise. The shock/shear-layer interaction emanates a broadband noise component. This may trigger the young shear layer at the nozzle, forming a feedback loop which results in a discrete noise component called screech. Both components are undesirable from structural and environmental (cabin noise) points of view. Screech tones are known to produce sound pressure levels of 160 dB and beyond. The focus of this research project lies in the numerical simulation of jet screech. Different numerical methods are shown with LES and DNS applications of a planar rectangular and three-dimensional jet with overset grid techniques to include complex geometries for the jet nozzle. Furthermore, a shock-capturing method is developed for high-order aeroacoustic computations. It consists in applying an adaptive second-order conservative filtering to handle discontinuities, in combination with a background selective filtering to remove grid-to-grid oscillations. The magnitude of the shock-capturing filtering is determined dynamically from the flow solutions using a procedure based on a Jameson-like shock detector. Results obtained for a shock-propagation problem are shown to validate the method, which will be now used for the simulations of supersonic jets. © 2009 Springer-Verlag Berlin Heidelberg.