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.