The effect of turbulence and shear on the flow around three dimensional square cylinders

Abstract

The effect of turbulence and shear on the flow around square cylinders has been investigated (i) for models without a free end at incidence a in the range 00<a< 45 0 for models with and without end plates and, (ii) for models with a free end at a=00 and a= 45 0 for model height H to width D ratio H/D in the range 2 :5 H/D 5 11. The Reynolds number, based on 4 the model width was 4.8 x 10 It has been found that end plates are necessary to simulate a two dimensional flow condition in uniform smooth flow provided the wall boundary layer is greater than about 10% of the model span. In other uniform flow conditions, away from the wall boundary layer affected region, which is about the physical thickness of the boundary layer, two dimensionality could be assumed. In linear shear flow., end plates reduced the base pressure in the low velocity region. Two dimensional model results agree well with the published results. Finite square cross-section cylinders exhibit a free end region of length ZF and a root region. Three regimes, Low H/D, Middle H/D and High H/D are found in all flow conditions. The drag on the finite cylinder in smooth flow is lower than that in turbulent flows. Provided the flow is turbulent, increasing turbulence decreases the drag. For a particular flow condition, increasing H/D ratio increases the drag. It appears that in the high H/D regime there is a shedding of the free end eddy. The shedding frequency is lower than the shedding frequency in the root region of the cylinder. The effect of shear can be ascertained by correcting the flow results for the local velocity and thus shear need not be considered a critical flow simulation parameter.