A study of the heat transfer and fluid mechanics of the turbulent separating and reattaching flow past a backward facing step using large eddy simulation

摘要

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. Three-dimensional simulations of isothermal flows and flows with heat transfer causing significant property variations are performed. A fully coupled, time-derivative preconditioned, colocated-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 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. Periodic boundary conditions in the spanwise direction for all variables were employed. All solid walls were maintained at the reference temperature of 293 K and no slip velocity boundary conditions were used. Inflow conditions were provided from an independent large eddy simulation of a turbulent plane channel flow.;From the simulations, the mean reattachment point was located at x/h = 6.1 as opposed to x/ h = 6.51 from the recent experiments of Kasagi and Matsunaga. Excellent agreement with the experiments in the mean quantities and turbulent statistics was obtained. Subsequently, the bottom wall downstream of the step was supplied with uniform wall heat flux levels of 1.0, 2.0, and 3.0 kW/m2, while all other walls were insulated. The viscous sub-layer played a critical role in controlling the heat transfer rate. Dramatic variation of the wall temperatures in the recirculation region was observed. The simulations captured the presence of a second counter-rotating eddy that affected the Nusselt number profiles. 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.