Numerical Study on the Influence of Upstream Groove Morphological Parameters on Flow and Heat Transfer Characteristics of Tandem Cylinders at Low Reynolds Numbers

The thermal performance is crucial in heat exchange and cooling systems, and surface structure optimization to enhance performance has become a key topic in fluid dynamics research. This study uses numerical simulations to investigate the effect of different surface patterns on the thermal behavior of a tandem cylinder system. The system consists of cylinders with identical diameters (D) and a spacing of 4D, where the upstream cylinder has grooves and the downstream cylinder is smooth. The study is conducted under laminar flow conditions (Re <= 200), analyzing three groove structures (square, triangle, and dimple) and exploring the impact of different groove frequencies (N = 2, 4, 6, 8, 10) on thermal performance. The results indicate that, at Re = 100 and N = 10, square grooves promote stable secondary vortices, thereby suppressing the continuous renewal of near-wall vorticity. In contrast, triangular and dimpled grooves enhance shear-layer oscillations and reattachment processes, resulting in a more uniform and strongly unsteady near-wall vorticity distribution. Moreover, the heat transfer efficiency increases with Re. Specifically, at Re = 200, dimpled and triangular grooves show a 2% and 2.4% improvement in heat transfer compared to square grooves. In general, higher groove frequencies reduce heat transfer efficiency, but at Re = 200 and N = 10, the heat exchange performance of dimpled and triangular grooves outperforms square grooves. The study also establishes a correlation between time-averaged Nusselt number to groove area, Re, and N.