Jet Screech Noise Computation

The near-field screech-tone noise of a typical underexpanded circular jet issuing from a sonic nozzle is simulated numerically. The self-sustained feedback loop is automatically established in the simulation. The computed shockcell structure, acoustic wave length, screech-tone frequencies, and sound pressure levels in the near field are in good agreement with existing experimental results. I. Introduction J ET noise is an important and still challenging topic in aeroacoustics. Many of its aspects are of primary practical importance, and the associated complicated physical phenomena are the topic of many experimental and theoretical investigations. In Refs. 1‐4, a comprehensive discussion and further references are provided. Under/overexpanded supersonic jets emit mixing noise, broadband shock-associated noise, as well as screech tones under certain conditions. The mixing noise is directly associated with large-scale structures, or instability waves, in the jet shear layer, and the broadband shock-associated noise is caused by the interaction of these waves with the shock-cell structure in the jet core. The screech tones arise due to a feedback loop involving the large-scale structures developing in the jet shear layer, their interaction with the jetcore shock-cell structure producing upstream propagating acoustic waves, and regeneration of the large-scale structures at, or in the vicinity of, the nozzle lip. This feedback loop leading to screech tones is sensitive to small changes in the system conditions, and the understanding of the phenomena to date is based mostly on experimental observations. 5−9 Screech is of particular interest not only because of general noise-reduction concerns, but also because of po