A low Reynolds number flow and heat transfer topology of a cylinder in a wake

Abstract

The flow and heat transfer topology of an isothermal cylinder (diameter D) in the wake of another smaller (diameter d) cylinder is numerically investigated for a spacing ratio of L/d = 5.5 and at a Reynolds number of 200. The governing Navier-Stokes and energy equations are solved using the finite volume method. The focus is given on how the size of the upstream cylinder influences the flow and heat transfer topology around the downstream cylinder when the diameter ratio d/D is varied from 0.15 to 1.0. The upstream-cylinder shear layers for d/D < 0.3 reattach on the downstream cylinder and shed vortices behind it. They for 0.3 ≤ d/D ≤ 1.0, on the other hand, shed vortices in the gap, and the wake of the downstream cylinder features a primary vortex street followed by a secondary vortex street. The primary street evolves into the secondary street through merging and isolated-shedding processes. The arrival of a gap vortex on the front surface of the downstream cylinder generates an impulse that has the greatest impact on the heat transfer. The surface-averaged heat transfer enhances when d/D is decreased from 1.0 to 0.4, and it declines for a further decrease in d/D. The enhancement in heat transfer is ascribed to an increased shear layer velocity, reduced wake-recirculation size, and enhanced recirculation strength. A novel tertiary frequency in heat transfer fluctuation is identified. The correlation between the flow and heat transfer fluctuation at the tertiary frequency is explicatively done through first Fourier transform and wavelet analysis.