Investigation of a turbulent convective buoyant flow of sodium over a backward-facing step

The influence of buoyancy-aided mixed convection on the heat transfer downstream of a sudden expansion of a plane channel is investigated by means of the steady-state Reynolds averaged Navier Stokes (RANS) simulation. A linear eddy viscosity model is used to compute the Reynolds stresses. The turbulent heat fluxes are modelled with a single gradient diffusion hypotheses using a local correlation to evaluate the turbulent Prandtl number. The velocity, turbulent kinetic energy and Reynolds shear stress profiles predicted are in good agreement with available DNS data. The local Stanton number trend is qualitatively well captured, however, its magnitude is underestimated for the mixed convection cases. Compared to the case of forced convection, the flow field and heat transfer change significantly. An influence of buoyancy is reported at very low Richardson numbers (Ri). A steady increase in heat transfer with rising influence of buoyancy is observed.