Large Eddy Simulation of the Turbulent Flow Past a Backward Facing Step

The heat transfer and fluid mechanics of a turbulent separating and reattaching flow past a single-sided backward-facing step are studied using large eddy simulation. A fully coupled, low Mach number preconditioned, collocated-grid, central differenced, compressible, finite volume formulation was developed to conduct the simulations. A sixth-order compact filter was used to prevent pressure-velocity decoupling. A compressible version of the dynamic subgrid scale model was used to model the effects of the smaller eddies. Navier-Stokes characteristic boundary conditions designed by Poinsot and Lele were used to provide boundary conditions. The isothermal turbulent flow past the step, at a Reynolds number of 5,540 based on the step height and upstream centerline velocity and a Mach number of 0.006, was simulated to validate the formulation. Subsequently, the bottom wall downstream of the step was supplied with constant wall heat flux levels of 1.0, 2.0, and 3.0 kWm2. The viscous sub-layer played a critical role in controlling the heat transfer rate. Streamwise and wall-normal turbulent heat fluxes were of the same order of magnitude. The Reynolds analogy did not hold in the recirculation region. However, the Stanton number profiles showed a striking similarity with the fluctuating skin-friction profiles.