Numerical simulation of vortex shedding from rectangular cylinders with different elongation ratios

RANS simulations are performed for flow past rectangular cylinders with different elongation ratios (L/D= 1, 2, 4, 6, 8, 10, 12, 14 and 16) at Re= 22 000 using the k-ω SST turbulence model. As L/D increases from 1 to 6, stepwise increase of Strouhal number (St) exists, whereas an almost linear variation of St with respect to L/D can be found (St= 0.1618*L/D) at L/D⩾ 8. In the flow, two small secondary vortices beneath the shear layers are identified and the trailing-edge secondary vortex presents opposite rotational direction comparing with the leading-edge main vortex. Analysis of the shear layer and vortex characteristics is carried out to correlate with the wall normal stress and shear stress on the rectangular cylinder surfaces. Further, four coupling modes between leading-edge vortex (L-vortex) and trailing-edge vortex (T-vortex) among cylinders with different L/D are observed, named L-Vortex Mode (i.e. L/D= 1–2), L-T-Vortex Mode (i.e. L/D= 4–8), T-L-Vortex Mode (i.e. L/D= 10–14), and T-Vortex Mode (i.e. L/D ⩾ 16). When L/D > 4, the convective velocity of the L- and T-vortex is not sensitive to the L/D.