2-WAY COUPLING IN SHEAR LAYERS WITH DILUTE BUBBLE CONCENTRATIONS

Direct numerical simulations are used to analyze the evolution of a te mporally growing two-dimensional shear layer seeded with dilute concen trations of bubbles under gravity. The bubble concentrations are dilut e enough so that bubble-bubble interactions can be neglected, but are large enough for cumulative effects of bubbles to influence the flow. The evolution of the bubble field is determined by tracking many indiv idual bubbles, and the flow field is advanced by using the Navier-Stok es equations with a coupling term representing the effect of the bubbl es on the flow. The results are interpreted in terms of the vorticity, density, and pressure fields relative to the one-way coupled or passi ve case. For the coupled case, a reduction in the magnitude of the vor ticity and pressure gradients near the vortex center is observed. In a ddition to modification of the flow, it is observed that the accumulat ion of bubbles is-smaller and the location of the equilibrium points a re shifted farther from the vortex center as a result of the coupling. It is explored how these changes are modified by different Froude num bers and bubble sizes. The differences between passive and coupled cas es usually increase due to larger accumulations as larger bubbles are considered. However, for certain Froude numbers an optimum coupling is observed at intermediate bubble sizes due to the absence of equilibri um points for large bubbles.