CURVED 2-STREAM TURBULENT MIXING LAYERS REVISITED

Two experimental studies of mildly curved (delta(omega)/(R) over bar a pproximate to 5%) two-stream mixing layers, using different fluids and covering a wide range of Reynolds numbers, are analyzed. One study wa s performed in a low-speed water channel at Stanford University, utili zing flow visualization and laser Doppler velocimetry. In this case, t he Reynolds number was low (Re-delta omega approximate to 7400), the i nitial boundary layers were laminar, and the velocity ratio was 0.5. T he other investigation was performed in the NASA Ames Mixing Layer Win d Tunnel, in which the three-dimensional structure and streamwise evol ution of curved mixing layers at high Reynolds numbers (Re-delta omega approximate to 5.7 x 10(4)) were studied, using hot-wire anemometry. Mixing layers with velocity ratios of 0.5 and 0.6, and both laminar an d turbulent initial boundary layers,were subjected to stabilizing and destabilizing longitudinal curvature (in the Taylor-Gortler sense). In stable and unstable mixing layers originating from laminar boundary l ayers, well-organized spatially stationary streamwise vorticity was ge nerated, which produced significant spanwise variations in the mean ve locity and Reynolds stress distributions. With the initial boundary la yers on the splitter plate turbulent, spatially stationary, streamwise vorticity was not generated in either the stable or the unstable mixi ng layer. Linear growth was achieved for both initial conditions, but the rate of growth for the unstable case was higher than that of the s table case. Correspondingly, the far-field, spanwise-averaged peak Rey nolds stresses were significantly higher for the destabilized cases co mpared with the stabilized cases, which exhibited levels comparable to , or slightly lower than, those for the straight case. Universal scali ng of the streamwise evolution of the vorticity thickness and Reynolds stresses, using the velocity difference parameter, lambda, and the mo mentum thickness of the high-speed boundary layer, theta(1), was reaso nably successful in grouping the straight, stable, and unstable mixing -layer results over the diverse range of conditions. (C) Elsevier Scie nce Inc., 1996