Effect of rectangular winglet pair roll angle on the heat transfer enhancement in laminar channel flow

Convective heat transfer enhancement can be achieved by generating secondary flow structures that are added to the main flow to intensify the fluid exchange between hot and cold regions in the system. One method involves the use of vortex generators to produce streamwise and transverse vortices on the top of the main flow. This study presents numerical computation results on laminar convection heat transfer in a rectangular channel which bottom wall is equipped with rectangular winglet pair vortex generators. The governing equations are solved using finite volume method by considering steady state, laminar regime and incompressible fluid. Three dimensional numerical simulations are performed to study the effect of the generators' roll-angle β on the flow and heat transfer characteristics. Different values of roll-angle β in the range [20°-90°] are considered, while maintaining a constant angle of attack (α = 30°) for all the cases. The influence of the Reynolds number is also studied for values 456 and 911 (based on the channel hydraulic diameter). Both local and global analyses of the thermal performances are carried out using parameters such as the Nusselt number and the friction coefficient. In addition, the position and strength of the longitudinal vortices created are presented and discussed, highlighting their effect on the heat transfer rates throughout the duct, for the various generators' roll-angles. Finally, from both local and global investigations, it is found that the optimal values of the roll-angle, determined for each Reynolds number, are not necessarily 90°, which corresponds to the widely used configuration in the open literature.