U or V Shape: Dissipation Effects on Cylinder Flow Implicit Large-Eddy Simulation

Implicit large-eddy simulation studies of low-speed circular cylinder flows at subcritical Reynolds numbers of both 2580 and 3900 are conducted. Focus is placed on the controversial profile shape of the streamwise velocity around one diameter downstream from the cylinder. The minimum dispersion and controllable dissipation scheme is employed for the reconstruction and the simple low-dissipation AUSM scheme is used as the Riemann solver. The combined numerical method performs well in the implicit large-eddy simulation of the separated flows. With the numerical method's feature of controllable dissipation, the nonmonotonic effect of the numerical dissipation on the predicted length of the recirculation bubble is studied and explained. When the numerical scheme is excessively dissipative, the increasing of dissipation tends to turn the flow into laminar vortex shedding, leading to a greatly underestimated recirculation bubble and a V-shape profile. However, when the numerical dissipation is small, its mechanism of suppressing the perturbations magnified by the numerical dispersion will become important. Increasing the dissipation will then increase the predicted recirculation size by delaying the shear-layer transition and tends to show a U-shape profile result. For implicit large-eddy simulation, the dispersion should be minimized and the dissipation should be controlled to an appropriate level.