Large eddy simulation of the turbulent flow past a backward-facing step with heat transfer and property variations

The heat transfer and fluid mechanics of a turbulent separating and reattaching flow past a backward-facing step are studied using large eddy simulation. A fully coupled, collocated-grid, low-Mach number preconditioned, compressible formulation employing central differences was developed to conduct the simulations. A sixth order compact filter was used to prevent pressure–velocity decoupling. A dynamic sub-grid scale procedure employing the compressible version of the Smagorinsky model has been used to capture the effects of the small scales. The isothermal turbulent flow past the step, at a Reynolds number of 5540 (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 a uniform wall heat flux; three simulations with increasing heat flux levels were conducted. 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.