CURVED 2-STREAM TURBULENT MIXING LAYERS - 3-DIMENSIONAL STRUCTURE ANDSTREAMWISE EVOLUTION

The three-dimensional structure and streamwise evolution of two-stream mixing layers at high Reynolds numbers (Re(delta) almost-equal-to 2.7 x 10(4)) were studied experimentally to determine the effects of mild streamwise curvature (delta/RBAR < 3%). Mixing layers with velocity r atios of 0.6 and both laminar and turbulent initial boundary layers, w ere subjected to stabilizing and destabilizing longitudinal curvature (in the Taylor-Gortler sense). The mixing layer is affected by the ang ular momentum instability when the low-speed stream is on the outside of the curve, and it is stabilized when the streams are reversed so th at the high-speed stream is on the outside. In both stable and unstabl e mixing layers, originating from laminar boundary layers, well-organi zed spatially stationary streamwise vorticity was generated, which pro duced significant spanwise variations in the mean velocity and Reynold s stress distributions. These vortical structures appear to result fro m the amplification of small incoming disturbances (as in the straight mixing layer), rather than through the Taylor-Gortler instability. Al though the mean streamwise vorticity decayed with downstream distance in both cases, the rate of decay for the unstable case was lower. With the initial boundary layers on the splitter plate turbulent, spatiall y stationary streamwise vorticity was not generated in either the stab le or unstable mixing layer. Linear growth was achieved for both initi al conditions, but the rate of growth for the unstable case was higher than that of the stable case. Correspondingly, the far-field spanwise -averaged peak Reynolds stresses were significantly higher for the des tabilized cases than for the stabilized cases, which exhibited levels comparable to, or slightly lower than, those for the straight case. A part of the Reynolds stress increase in the unstable layer is attribut ed to 'extra' production through terms in the transport equations whic h are activated by the angular momentum instability. Velocity spectra also indicated significant differences in the turbulence structure of the two cases, both in the near- and far-field regions.