The turbulent shear layer at high Reynolds number is a canonical turbulent flow found in a variety of scenarios, from chemical lasers to jet-engine combustors. The mixing properties of the flow, both at large and small scales, are known to depend on a host of parameters, both local and global; in particular, the effects of the initial/inflow conditions, the flow compressibility, and the Reynolds number will be discussed here. Experiments were performed in the GALCIT Supersonic Shear Layer Facility and employed the (non-premixed) (H₂+ NO)/F₂ chemical system, in the fast-kinetic regime, to infer the structure and amount of molecular-scale mixing in a Reynolds number regime (Re<~10⁶) inaccessible to direct-measurement techniques, e.g., laser-induced fluorescence.

Inflow conditions were varied by perturbing each, or both, of the boundary layers on the splitter plate separating the two freestream flows, upstream of shear-layer formation. The results of chemically-reacting flip experiments reveal that seemingly small changes in inflow conditions have an undiminished effect on not only the large-scale structure and shear-layer growth rate, as had been documented previously, but also on molecular mixing and chemical-product formation, far downstream of the inflow region. An increase in flow compressibility, when decoupled from the other significant parameters of the flow, e.g., Reynolds number, decreases the large-scale growth, consistent with previous investigations, but increases the molecular-scale mixing within the turbulent shear-layer region. A new parameter for shear-layer compressibility successfully reconciles previous observations of shear-layer growth.

Both the dynamics and mixing of the turbulent shear layer depend on a variety of parameters in a complex, coupled manner. In addition, local descriptions of the flow are inadequate; the global-flow environment, e.g., initial/inflow conditions, must be regarded to be at least as important as local parameters.

References:

Slessor, M. D., Bond, C., and Dimotakis, P., 1998 "Turbulent shear-layer mixing at high Reynolds numbers: effects of inflow conditions," GALCIT Technical Report FM98-1.