Simulations for Microbubble Drag Reduction (MBDR) at High Reynolds Numbers

Simulations of turbulent channel flows at Re = 135 400, seeded with microbubbles, have been used to investigate the dynamics of microbubble drag reduction. The bubbles are found to exert an effective streamwise body force on the flow that retards the near-wall flow and results in a reduction in drag. Besides this density effect of the bubbles there is a suspension viscosity effect, and both depend on the local void fraction and bubble size. In addition, collisions or contacts between bubbles can lead to an enhanced dispersion at larger void fractions. These features are investigated for a range of conditions to guide the development of RANS models.