Numerical study on characteristics of flow and thermal fields of offset cylinder arrays in the middle Reynolds number range

• When Ps/D ≥ 4, the wake flow of the upstream cylinders becomes unsteady to enhance the heat transfer enhancement.
• The recovery of U¯ and T¯ reduces the effective Re and temperature difference of the approaching flow to the downstream cylinders, respectively.
• The strength of uv¯ and vθ¯ is positively related with the heat transfer enhancement of the downstream cylinders.
• The combination of various effects is a way of heat transfer enhancement.

In order to offer a detailed explanation for heat transfer enhancement caused by the instability, a computational model for offset cylinder arrays was established by using a compound grid system. The fully implicit forms of continuous equation, unsteady Navier–Stokes equations and energy equation were finite-differenced. The numerical results demonstrate that cylinder row pitch plays an important role on the flow effects, which enhance or deteriorate the heat transfer on cylinder surfaces. Among these flow effects, the acceleration effect and the instability effect are the main factors for enhancing the downstream cylinders. Moreover, heat transfer enhancement caused by the flow instability is an effective way to reach the aim of reducing flow resistance and promoting heat transfer.