Buoyancy Effect on the Flow Pattern and the Thermal Performance of an Array of Circular Cylinders

Abstract

In this paper we found, by means of numerical simulations, a transition in the oscillatory character of the flow field for a particular combination of buoyancy and spacing in an array of six circular cylinders at a Reynolds number of 100 and Prandtl number of 0.7. The cylinders are iso-thermal and they are aligned with the Earth acceleration (g). According to the array orientation, an aiding or an opposing buoyancy is considered. The effect of natural convection with respect to the forced convection is modulated with the Richardson number, Ri, ranging between −1 and 1. Two values of center to center spacing (s = 3.6d − 4d) are considered. The effects of buoyancy and spacing on the flow pattern in the near and far field are described. Several transitions in the flow patterns are found and a parametric analysis of the dependence of the force coefficients and Nusselt number with respect to the Richardson number is reported. For Ri = −1, the change of spacing ratio from 3.6 to 4 induces a transition in the standard deviation of the force coefficients and heat flux. In fact the transition occurs due to rearrangement of the near field flow in a more ordered wake pattern. Therefore, attention is focused on the influence of geometrical and buoyancy parameters on the heat and momentum exchange and their fluctuations. The available heat exchange models * for cylinders array provide a not accurate prediction of the Nusselt number in the cases here studied.

Mixed convection heat transfer from a heated circular cylinder

“…investigated the influence of mixed convection on heat transfer around three confined circular cylinders placed in tandem arrangement. Fornarelli et al (2016) tested the effect of aiding and opposing thermal buoyancy on vertical configuration of flow around six circular cylinders placed in-line arrangement.…”

Convective Effects in a Latent Heat Thermal Energy Storage

“…The melting/solidification time, temperature time-series in different points, or the dynamic of the melting front are the main results of both numerical simulations [42][43][44] and experiments [45,46]. In some papers [18,45,47,48], snapshots of the simulated velocity field in shell-and-tube configurations are reported. The experiments and numerical results highlight that the melting phase is more affected by the convective motion with respect to the solidification process.…”

“…The experiments and numerical results highlight that the melting phase is more affected by the convective motion with respect to the solidification process. Indeed, during the solidification the convective velocity is low and decreases during the process due to the solidification of the PCM [47]. The flow field details help the scientists to explain some convection effects on the heat transfer in the melted PCM.…”

Analysis of laminar flow across a triangular periodic array of heated cylinders

“…Crowdy [37] solved the problem of uniform flow past a linear periodic array of cylinders in tandem or crossflow and proposed a quasi-analytical mathematical approach and derived useful approximations for the blockage coefficients between the cylinders. Fornarelli et al [38] studied the effect of buoyancy and spacing between the cylinders on the flow pattern and thermal field in the in-line array of six cylinders at Re = 10 and Pr = 0.7 and Richardson number Ri varying from -1 to 1 and spacing between the cylinders varying from 3.6 to 4D. Their results show that the time-averaged drag coefficient of the array increases linearly for forced convection and aiding buoyancy.…”