Buoyancy effect on the flow pattern and the thermal performance of an array of circular cylinders

TL;DR

This study uses numerical simulations to analyze how buoyancy and spacing influence flow patterns and thermal performance in an array of circular cylinders, revealing flow transitions and limitations of existing heat exchange models.

Contribution

It identifies flow pattern transitions caused by buoyancy and spacing changes, providing new insights into heat transfer and force fluctuations in cylinder arrays under natural convection.

Findings

Flow transitions depend on Richardson number and spacing.

Flow becomes more ordered at certain parameters.

Existing heat exchange models are inaccurate for studied cases.

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.