Vortex Shedding Characteristics of Tapered Cylinders at Turbulent Wake

Vahid Tamimi; Mostafa Zeinoddini; Arash Bakhtiari

Abstract

The physics of flow regime around a tapered cylinder is strongly three-dimensional (3D) and complex. These pose numerical difficulties in capturing the vortex shedding phenomena in the wake of cylinder. This paper discusses the main characteristics of vortex shedding behind a fixed linearly tapered circular cylinder at relatively high Reynolds numbers. A computational fluid dynamics model is employed to solve the 3D incompressible transient Navier-Stokes governing equations. The numerical model is first calibrated/validated against available experimental and Direct Numerical Simulations data for vortex shedding past circular cylinders from other researchers. The calibrated model is then employed to explore vortex shedding characteristics behind a stationary and mildly tapered cylinder. A range of Reynolds number up to 29,000 is considered. The model is able, reasonably well, to simulate key physical vortex shedding characteristics for tapered cylinders. Phenomena such as variation of the shedding frequency along the cylinder span or cellular vortex shedding, vortex dislocations or vortex splitting, oblique vortex shedding, streamwise or longitudinal vortices and the variation of the vorticity patterns along the tapered cylinder are discussed. Lift and drag force coefficients of the tapered cylinder are also presented. Keywords: Tapered cylinder, cellular and oblique vortex shedding, vortex dislocations, lift and drag forces