Structure and Mixing in Turbulent Shear Flows

The broad problem being addressed in our research is to identify and describe the primary vortical ("coherent", "organized") large structures in various turbulent shear flows; to determine how they contribute to the mixing processes; and to make use of them in modelling and in possibly controlling or modifying those flows. Accumulating experimental evidence suggests that these primary vortical structures are different in different shear flows. Conclusions which follow from these views are that (i) there cannot be a universal turbulence model for these different flows; and (ii) existence of such structures implies the possibility of their manipulation or control and thus modification of the flow itself. These organized structures (and their response to excitation) are manifestations of instability response to natural or imposed disturbances and thus may be important in cooperation with other, physical processes, e.g. , acoustic coupling, rate controlled chemistry, etc., in problems like combustion chamber instability.