Heat transfer enhancement in a poiseuille channel flow by using multiple wall-mounted flexible flags

The flapping dynamics of multiple wall-mounted flexible flags vertically clamped in a heated channel and their effects on heat transfer performance were explored numerically. The fluid-structure-thermal interaction between the flapping flexible flags and the surrounding fluid was modeled with the penalty immersed boundary method. The vortex mixing process was examined to analyze their effects on heat transfer enhancement. The effects of varying the gap distance G/d, the reduced distance d/L, the bending rigidity gamma, the channel height H/L and the Reynolds number Re on heat transfer enhancement were scrutinized to optimize cooling, where the flag length is L. The thermal enhancement factor was determined to assess both the heat transfer enhancement benefit and the pressure drop penalty. The asymmetric flag configuration G/d = 0.5 results in better cooling performance than the symmetric configuration G/d = 0 because of the resulting thermal mixing of the cold mainstream and the near-wall hot fluid. More flags can be clamped inside the channel by varying the reduced distance d/L. Multiple flags with gamma = 0.04 provide the maximum convective heat transfer at Re = 600. Increasing the blockage ratio, i.e. the ratio of the cross-sectional height occupied by the flags to the channel height, enhances the friction factor. (C) 2020 Elsevier Ltd. All rights reserved.