Unsteady Reynolds-averaged Navier-Stokes: toward accurate prediction of turbulent mixing phenomena

Traditional steady-state simulation and turbulence modelling are not always reliable. Even relatively simple flow conditions phenomena such as buoyancy, flow oscillations and turbulent mixing can necessitate the use of computationally expensive unsteady simulation. Under these circumstances, the unsteady Reynolds-averaged Navier-Stokes (URANS) approach can offer accurate solutions without the prohibitive computational expenditure of large eddy simulation (LES) or direct numerical simulation (DNS). A particular benefit of the URANS methodology over LES type approaches is that it does not require complex boundary formulations at inflow or outflow boundary conditions. In order to test this methodology, the URANS approach is applied to three challenging nuclear engineering scenarios in which turbulent mixing plays a major role: parallel jets, fuel bundles and T-junctions. For each case, the capability of the methodology to accurately reproduce the flow field was assessed, and the results demonstrated that URANS holds promise to be the industrial standard in nuclear engineering applications that do not involve buoyancy.