| It is well known that external 2-D perturbations at frequencies low compared to the natural roll-up frequency lead to enhanced growth rates in a two-stream shear layer. The purpose of the present study was to quantify various aspects of the molecular mixing taking place in such flows. Experimental measurements were obtained for the amount of molecular mixing and the mixture composition in a chemically reacting turbulent shear layer subjected to 2-D perturbations, over a range of frequencies and amplitudes. In addition, the effect of 3-D forcing and combined 2-D/3-D forcing on the mixing field were studied. The results show that the fraction of the shear layer width filled with mixed fluid initially decreases and then increases with forcing frequency. Somewhat surprisingly, even though the addition of 3-D perturbations did cause spanwise undulations in the mixed fluid amount, the layer width and the average mixed-fluid concentration, it did not change the trend in the mixed-fluid fraction found for purely 2-D forcing. This indicates that streamwise vorticity injection does not necessarily lead to further increases of the mixing enhancement in this study in a liquid phase, high Schmidt number shear layer.; In a work independent from the above, the need for both mixing and kinematic data has led to the development of a technique to simultaneously measure velocity and concentration in a mixing layer. Although the technique is still in an evolutionary stage, the potential of this approach is demonstrated. |
