Flow patterns and heat transfer around six in-line circular cylinders at low Reynolds number

TL;DR

This study uses numerical simulations to analyze flow patterns and heat transfer around six in-line cylinders at low Reynolds number, revealing how spacing affects flow regimes and heat transfer efficiency.

Contribution

It identifies two flow patterns and quantifies how spacing influences heat transfer enhancement in in-line cylinder arrays.

Findings

Flow pattern transition occurs between SSL and SLSV modes.

Heat transfer increases by up to 25% when spacing decreases from 4d to 3.6d.

Phase shift between Nusselt number series correlates with heat transfer enhancement.

Abstract

The flow field and the heat transfer around six in-line iso-thermal circular cylinders has been studied by mean of numerical simulations. Two values of the center to center spacing ($s=3.6d$ and $4d$, where $d$ is the cylinder diameter) at Reynolds number of $100$ and Prandtl number of $0.7$ has been investigated. Similarly to the in-line two cylinder configuration, in this range a transition in the flow and in the heat transfer occurs. Two different flow patterns have been identified: the stable shear layer (SSL) mode and the shear layer secondary vortices (SLSV) mode, at $3.6$ and $4$ spacing ratio ($s/d$), respectively. At $s/d=3.6$ the flow pattern causes the entrainment of cold fluid on the downstream cylinders enhancing the heat transfer. On the other hand at $s/d=4$ two stable opposite shear layer prevent the cold fluid entrainment over the downstream cylinders reducing their heat exchange. The overall time average heat transfer of the array is enhanced up to 25% decreasing the spacing ratio from $4$ to $3.6$. Furthermore, it is found that the increased heat transfer is related to the phase shift between the Nusselt time series of successive cylinders.