Three-dimensional wake dynamics of curved cylinders

Three-dimensional computations have been performed in order to study the fundamental mechanisms of vortex shedding past curved circular cylinders in directions normal and parallel to the plane of curvature at Reynolds numbers of 100 and 500. The basic shape upon which all the geometries were built was that of a quarter ring. The spatial discretization of the three-dimensional Navier-Stokes algorithm was based on the spectral//ip element method. For the cases where the flow was normal to the plane of curvature, a quarter ring geometry and a curved cylinder ending semi-buried in the ground were studied. Different flow conditions were applied including a uniform or sheared velocity profile and a slip or a no-slip wall. The effect of a sheared velocity profile was found to be dominant to that of the wall boundary and resulted in vortex linking and lack of correlation along the span. For the cases where the flow was parallel to the plane of curvature, different configurations were investigated with respect to the leading edge orientation. When the flow was directed onto the outside of the bend, three-dimensional shedding was observed not governed by the variation of local normal Reynolds numbers considered by a sectional approach. With the free-stream aligned onto the inside of the bend, however, no conventional shedding was detected. The axial flow directed towards the top of the geometry and the production of streamwise vorticity played a key role in stabilizing the wake. The steady wake features persisted on the whole even when a straight cylinder extension was added on top of the curved body. The feeding of the axial flow, stemming from the curved part, into the straight cylinder extension, weakened the shedding process expected from a straight cylinder at these Reynolds numbers. Maximum w velocity components of the order of the free-stream at Re = 500 were located in the wakes of these bodies. Experimental work was also conducted alongside. The towing tank flow visualizations were found to be in qualitative agreement with the computational findings. Overall, the importance of investigating these curved cylinder flows with a fully three-dimensional approach has been demonstrated, especially for the second set of computations.Open Acces