The effect of fluid shear on oscillating bubbly flows

The impact of fluid shear on the bubble distribution in channel flows with periodically oscillating pressure gradient is examined by direct numerical simulations. Equal-sized and nearly circular bubbles are placed randomly in the channel at the initial time. In the absence of shear, the bubbles form columns spanning the width of the channel, but a strong enough shear breaks up the columns, leading to a more random bubble distribution. The effect of the nondimensional shear rate on the flow can be divided into low shear rate, moderate shear rate, and high shear rate regimes. The flow dynamics is also influenced by the Reynolds and the Euler number, and when these numbers decrease, the low shear rate regime, with stable tilted columns of bubbles, becomes smaller. Comparison of results for two- and three-dimensional flows shows that the dynamics observed in two-dimensional flows is also found in three dimensions.