Direct numerical simulation of turbulent flow over a backward-facing step
Kopera, Michal Andrzej
arxiv: Physics::Fluid Dynamics
A three-dimensional, turbulent \ud flow in a channel with a sudden expansion\ud was studied by direct numerical simulation of the incompressible Navier-Stokes\ud equations. The objective of this study was to provide statistical data of backwardfacing\ud step \ud flow for turbulence modelling. Additionally, analysis of the statistical\ud and dynamical properties of the \ud flow is performed.\ud The Reynolds number of the main simulation was Reh = 9000, based on the\ud step height and mean inlet velocity, with the expansion ratio ER = 2:0. The discretisation\ud is performed using the spectral/hp element method with stiffly-stable\ud velocity correction scheme for time integration. The inlet boundary condition is\ud a fully turbulent velocity and pressure field regenerated from a plane downstream\ud of the inlet. A constant \ud flowrate was ensured by applying Stokes \ud flow correction\ud in the inlet regeneration area.\ud Time and spanwise averaged results revealed, apart from the primary recirculation\ud bubble, secondary and tertiary corner eddies. Streamlines show an additional\ud small eddy at the downstream tip of the secondary corner eddy, with the\ud same circulation direction as the secondary vortex. The analysis of the 3D, timeonly\ud average shows the wavy spanwise structure of both primary and secondary\ud recirculation bubble, that results in spanwise variations of the mean reattachment\ud location. The visualisation of spanwise averaged pressure \ud uctuations and\ud streamwise velocity showed that the interaction of vortices with the recirculation\ud bubble is responsible for the \ud apping of the reattachment position. The\ud characteristic frequency St = 0:078 was found.\ud The analysis of small-scale energy transfer was performed to reveal large\ud backscatter regions in strong Reynolds stress areas in the mixing layer. High\ud correlation of small-scale transfer with non-linear interaction of large-scale velocity\ud and small-scale vorticity was found.\ud The data of the \ud flow fields was archived. It contains the averages for velocities,\ud pressure and Reynolds stress tensor, as well as 3D instantaneous pressure and\ud velocity history.
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