Direct Numerical Simulation of flow separation with heat conductionOder, Jure (Avtor) Tiselj, Iztok (Mentor) DNSconfined backward facing flowsodium flowNek5000The subject of the present thesis is the direct numerical simulation (DNS) of a confined backward facing (BFS) step geometry with a flow of two fluids with Prandtl numbers 0.005 and 0.1. The expansion ratio of the BFS geometry is equal to 2.25 and the outflow of the geometry has a square shape. The geometry is surrounded by no-slip walls and has no periodic boundaries. Additionally, a step wall and a heater downstream of the step are simulated. These are thermally coupled with each other and to the fluid domain. A recycling boundary condition is used to achieve a fully turbulent inflow boundary condition with a constant mass flow rate. The friction Reynolds number of the flow in the channel upstream of the step is around 207 and the Reynolds number based on the bulk velocity at the inflow and the hydraulic diameter of the inflow is approximately 7100. The reattachment zone was found at about 7.9 step heights downstream of the step. Because the step is confined in the span-wise direction, the average flow exhibits strong three-dimensional features. These features significantly increase the averaging time needed to achieve sufficiently low statistical uncertainties of flow properties. The DNS is performed with moderate spatial resolution on 30 million grid points, however, it took very long averaging time and 12 million time steps to obtain acceptable statistical uncertainties. In the thesis, the three-dimensional are explored and first and second order statistics are given for flow and thermal fields, which are relevant for the validation of Reynolds averaged Navier-Stokes modelling approaches. In the last section of the thesis, statistical uncertainties of the simulated variables in specific monitoring points are analysed. The statistical uncertainties were found to be higher for points located near the stagnation zones.20192019-12-22 07:45:12Doktorsko delo/naloga113361sl