Model for turbulent backflows
Introduction T URBULENT backflow regions exhibit a strong wake-like behavior down to the immediate vicinity of solid surfaces. This behavior precludes the use of the law-of-the-wall as a tool for analyzing such flow regions and dictates development of turbulence models dedicated to treating these flows. Such a model was developed and used successfully to predict a large class of flows involving detached flow regions. It was an algebraic model applied as a module within a "host" model (such as a ke model) to determine the eddy-viscosity field inside backflow regions. Experiments in turbulent recirculation zones' indicate that there is a wide class of such flows in which the backflow region is characterized by negligible turbulence production. In such cases, the balance of turbulence energy is between diffusion of energy from the outer (large-scale turbulence) flow into the reversed flow region and its dissipation within that region. This mechanism is used as a basis for a new turbulence model geared for backflow regions. The model, featuring the analytical solution of an ordinary differential equation (ODE) normal to walls, is introduced and tested. Like the previous model, it is used as a module within a host model to determine the eddy viscosity throughout backflow regions; unlike the previous model, it requires a host model that solves a field equation for the turbulence kinetic energy.