On the three-dimensional flow development around circular finned cylinders

Abstract

The three-dimensional flow development around the circular finned cylinders is investigated numerically. Three finned cylinders with constant fin pitch (p), fin thickness (t), and effective diameter (Deff) and a range of diameter ratios (Df/Dr) within 1.25 ≤ Df/Dr ≤ 2.5 are considered in this study. One bare cylinder with a diameter equivalent to the effective diameter of the finned cylinders is also considered. The numerical simulations are performed using the large eddy simulation turbulence model for a free-stream velocity corresponding to the Reynolds number Re = 3900, defined based on the effective diameter (Deff). This study provides novel insights into the flow physics in the channel between the fins and its effect on the three-dimensional flow development. The results accentuate that the three-dimensional flow development around the finned cylinders fundamentally differs from that of the bare cylinder. In particular, the flow separation topology at the surface of the finned cylinders differs significantly from that of the bare cylinder due to flow entrainment between the fins. The distinct flow separation leads to the formation of streamwise edge vortices, which induces downwash flow in the near wake of the finned cylinders. The combined effect of the entrainment between the fins and downwash flow affects the vortex formation length and mean pressure distribution around the cylinder. As a result, the structural loading on the surface of the finned cylinders is distinctively different from that of the bare cylinder with profound dependence on the fin parameters.