Applying a non-equilibrium wall function in k-ε turbulent modelling of hydrodynamic circulating flow

摘要

Wall bounded flow with severe adverse pressure, separation, reattachment and stagnation has non-equilibrium (NE) exhibition. A wall function in turbulent flow is a remedy to avoid resolving near wall complex phenomena using predetermined functions as boundary conditions. The advantage of this case is permission to use a relatively coarse near wall cells and hence saving CPU time. Standard wall function (SWF) is a semi-empirical function that is just valid for constant shear near wall cell and local equilibrium flow. Popovac and Han-jalic introduced a non-equilibrium wall function as (PWF) with a blending method in v~2-f model. To investigate PWF in circulating flow, standard k-ε model that has key role in complex and expensive industrial problems is used in this study. The approach derived by Popovac and Hanjalic retains the functional form of the SWF and can be easily implemented in existing code. Simulation results are validated against direct numerical simulation (DNS) on channel and experimental data on backward facing step (BS) and a sharp U bend flow. Prediction with PWF shows that use of this wall function in k-ε model has not any sensitive change in near equilibrium flow. However, produces an improvement in NE conditions like flow in circulation zones.