DIRECT NUMERICAL SIMULATIONS OF MULTIPHASE FLOWS

Direct numerical simulations (DNS) have recently emerged as a viable tool to understand finite Reynolds number multiphase flows. The approach parallels DNS of turbulence, but the unsteady motion of a deforming phase boundary adds considerable complexity. Here, we briefly describe one particular method for DNS, front-tracking, and then review results for bubbly flows. Several simulations have shown that bubble deformation plays a very significant role in both determining the microstructure of the flow (the most probable bubble distribution) as well as the large-scale behavior of the system. Results for homogeneous bubbly flows and drag reduction due to bubble injection into a turbulent channel are discussed briefly and an investigation of the flow of nearly spherical bubbles in vertical channels is described in more detail. In all cases, DNS has lead to a fundamental new understanding of the flow.