A NUMERICAL INVESTIGATION OF BROAD-BAND SHOCK NOISE

The interaction between a spatially developing, turbulent shear layer (Mc — 0.6) and an isolated oblique compression wave (AP/P^ = 0.2) is studied by direct numerical simulation. Analysis is performed on three key elements of this problem, namely the oblique compression-expansion wave, the associated acoustic field and the shear-layer turbulence. The acoustic field consists of two separate components: the downstream propagating mixing noise originating from the transitional region of the shear layer, and a nearly omni-directional shock noise component from a region slightly downstream of the interaction location. The shock noise component dominates the upstream radiation but its relative importance diminishes in the downstream direction. The frequency spectrum of the shock noise has a peak centered around fS^/AU = 1.17, which is slightly higher than that of mixing noise. In the near field, self-similar turbulence is shown to be established before the interaction. Two-point correlation of the turbulent fluctuations confirms the importance of accounting for the spatial coherence of the turbulence in any shock noise model. Minimal oscillations of the compression wave are observed. This is in sharp contrast to the two-dimensional shock-vortex study by Manning & Lele [8] in which substantial shock motion was observed.