ESTIMATION OF SHEAR-INDUCED LIFT FORCE IN LAMINAR AND TURBULENT FLOWS

The goal of the present study is to demonstrate that direct numerical simulations (DNS) coupled with interface tracking methods can be used to estimate interfacial forces in two-phase flows. Current computational multiphase fluid dynamics codes model interfacial forces utilizing closure laws that are heavily dependent on limited experimental data and simplified analytical approximations. In the present work, a method for improving the current interfacial force database has been developed by using DNS to quantify the lift and drag forces on a single bubble in laminar and turbulent shear flows. A proportional-integral-derivative based controller was implemented into the finite element based, multiphase flow solver [PHASTA (Parallel, Hierarchic, higher-order accurate, Adaptive, Stabilized, finite element method Transient Analysis)] to control the bubble position. This capability allowed for utilization of a steady-state force balance on the bubble to determine lift and drag coefficients in various shear flows. Specifically, for low shear flows (2.0 s(-1)), the effect of the wall presence is analyzed, and for high shear flows, the effect of turbulence is studied. A number of uniform shear (10.0 to 470.0 s(-1)) laminar flows were simulated to assess lift and drag force behavior as the kinetic energy of the flow increased. Two high shear (236.0 and 470.0 s(-1)) turbulent flows were simulated to understand bubble-turbulence interaction influence on the drag and lift phenomena. Two uniform shear rates (20.0 and 100 s(-1)) were simulated utilizing pressurized water reactor fluid properties. The lift and drag coefficients estimated in this work are in agreement with models developed for low shear laminar flows, whereas for high shear laminar and turbulent flows, bubble-turbulence interaction became a dominating influence in the lift and drag coefficient estimation. The novel results and method presented in this paper offer a path to simulating full-fledged reactor coolant environments where the lift and drag forces on a single bubble can be studied.