Large Eddy Simulation of the Flow Past a Circular Cylinder at Super-Critical Reynolds Numbers

Turbulent flows past bluff bodies involve very complex phenomena such as separation, reattachment and vortex shedding. Such flows are commonly observed in many applications and the flow around a circular cylinder is usually considered as a benchmark problem in this area. The laminar to turbulent transition in this case is limited by the particular geometry and flow conditions, i.e. transition is not induced by the body geometry itself but rather by the interactions of different unstable regions in the flow. Three different zones can be found: the boundary layer in the cylinder, two shear layers on top and bottom of the body and, finally, the wake.  

Although Reynolds-averaged Navier–Stokes (RANS) models have been applied successfully in many practical computations and appear to yield accurate predictions in attached flows as well as some with shallow separations, they tend to fail for massively separated flows. Large eddy simulation (LES), which directly calculates the large turbulent scales dependent on geometry with the fine scale turbulence modelled, attempts to provide higher accurate results. However, it remains too expensive for LES to be widely used in practical applications due to the excessive computing power requirements in high Reynolds number (Re) boundary layers.

In this study, to simulate the flow past a circular cylinder using LES, a novel combination of O- and H-grid structures is used to reduce mesh points and, in turn, the computational cost.  As already addressed in [1, 2, 3] for flows past a circular cylinder, there is a jump in the Strouhal number at about Re=350,000  and the flow experiences Strouhal numbers around St=0.45 for Reynolds numbers between 400,000 and 2,000,000 (super-critical regime). In the present work, to investigate this phenomenon numerically, the flow past a circular cylinder is simulated by LES for Reynolds numbers 300,000, 500,000 750,000, 1,000,000 and 1,250,000, and results are compared with experimental data presented in [1, 2, 3].

Reference

[1] Bearman PW. On vortex shedding from a circular cylinder in the critical Reynolds number regime. J Fluid Mech 1969;37:577–85.

[2] Schewe G. On the force fluctuations acting on a circular cylinder in cross-flow from subcritical up to transcritical Reynolds numbers. J Fluid Mech1983;133:265–85.

[3] Wen P, Qiu W. Numerical Studies of VIV of a Smooth Cylinder. In: Proceedingsof the 27th ITTC Workshop on Wave Run-up and Vortex Shedding. 2013.