Unsteady RANS and LES Simulation of an Ideal Rankine Vortex Decay

The 3D numerical simulation was carried out for an idealized Rankine vortex using nonlineark-εmodel (one kind of RANS model) and large eddy simulation (LES) techniques. In this 3D simulation, the vortex flow field was given to rotate with the vertical axis in a free surface rectangular domain. In order to investigate the predictability of standard (linear) and non-lineark-εmodels, the decay of a trailing vortex was simulated and compared with previous DNS data. The governing equations for mean velocities and turbulent flows were discretized with the finite volume method based on a staggered grid system. It was observed that in the growth phase as well as in stabilized phase of turbulence, the decay rate of tangential velocity by RANS model was well comparable with LES simulation as well as previous DNS data. However, in the decay phase of turbulence, RANS model showed slightly faster decay of tangential velocity due to its slower decay of turbulence compared to LES or DNS. The patterns as well as magnitudes of secondary currents predicted by RANS and LES models were well comparable to each other.

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