The effect of extra-strain rates of streamline curvature and divergence on mixing layers

Measurements have been made in two axisymmetric single-stream mixing layers, each subjected simultaneously to curvature and divergence. The boundary layer was turbulent at separation. In the 'very-strongly-strained' layer, the curvature was entirely of the stabilizing sense. The large-scale structures are suppressed but not destroyed, and divergence leads to a much more rapid recovery than would be expected from curvature alone. In the 'moderately-strained' layer, destabilizing curvature followed the stabilizing curvature. The Reynolds stresses and triple-velocity products varied qualitatively as the lagged strains, though, quantitatively, destabilizing effects are unlikely to have been absent in the lagged region of stabilizing curvature. The approach of an undistorted layer to asymptotic stress levels is distinctly non-monotonic.