Flow and heat transfer around a diamond-shaped cylinder at moderate Reynolds number

Abstract

Hydrodynamics and heat transfer around a diamond-shaped cylinder in a stationary flow have been investigated using direct numerical simulation. Simulations were carried out for a steady flow with a Reynolds numbers ranging from 1 to 70 and for a Prandtl number corresponding to a gas (Pr=0.7). The study focuses on the influence of the diamond apex angle α (33⩽α≤120°) on the evolution of drag, wake length and Nusselt number. A comparison with the case of a circular cylinder is performed. It is shown that the drag coefficient of a diamond-shaped cylinder remains very close to the one of a circular cylinder (±10%) for Re<10 and that it is reduced by decreasing the apex angle for Re>10. In the same time, compared to the circular cylinder case, the reduction of the apex angle postpones significantly the Reynolds corresponding to the wake recirculation onset. When the Reynolds reference velocity is, as often, taken as the far field velocity, the corresponding Nusselt numbers are found to decrease with the apex angle α. However, it is found that when the reference velocity is based on the maximal vorticity near the equator, the Nusselt number of diamond-shaped cylinders seems to collapse on a single master curve. This may indicate that the relevant velocity scale to describe Nusselt variation, and thus the heat transfer, is dependant on the interfacial vorticity intensity rather than on the far field velocity.