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

The flow field and the heat transfer around six in-line iso-thermal circular cylinders have been studied by means of numerical simulations. Two values of the center to center spacing "" and 4d, where dis the cylinder diameter) at Reynolds number of 100 and Prandtl number of 0.7 have been investigated. Similarly to the in-line two cylinders 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 ratios respectively. At "" the flow pattern causes the entrainment of cold fluid on the downstream cylinders enhancing the heat transfer. On the other hand, at "" two stable opposite shear layers 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.