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 sh...

This work demonstrates a strategy for hybrid turbulence modeling that relies on parameters identifying flow structures to regulate the model's level of scale resolution, independent of the computational grid and user input. The approach can be classified as second-generation unsteady Reynolds-averaged Navier–Stokes (URANS), where it is assumed that increased scale resolution inside rapidly deformed turbulence regions can consistently reduce modeling error compared to basic URANS closures. The methodology selects flow structures by evaluating the second invariant of the velocity gradient tensor in the resolved field. The functions used for this purpose are similar to techniques applied in topology studies to identify coherent structures. The proposed formulation extends a baseline nonlinear eddy-viscosity URANS model and achieves completeness by means of a differential Lagrangian operator that approximates a locally computed average. The model addresses the lack of general applicability deriving from globally filtering at small scales by reverting to the baseline URANS in flow locations with low acceleration, in which the URANS solution achieves best accuracy. Three flow test cases are presented, demonstrating substantial accuracy enhancement over the baseline URANS on the same grid sizes. Results obtained with this new closure demonstrate robust applicability to internal flows, showing large-eddy simulation (LES)-like statistics on coarse RANS computational grids. The observed increase in computational cost compared to the baseline URANS is only 3% to 24%, which represents almost two orders of magnitude reduction from LES.