Heat transfer enhancement in a microchannel via passive vortex generators combining with cylinder and symmetrically clamped elastic flaps

The heat transfer process of a heated channel with multiple elastic flaps symmetrically clamped in the wake of a stationary cylinder were simulated by a fluid-structure-thermal coupling solver. We probe the effect of layout parameters of passive vortex generators on specific physical quantities in this study, notably the local Nusselt number and Colburn factor. Finally, through the analysis of multi-physical fields the mechanism of the optimal layout is revealed. The numerical results suggest that the wake of the cylinder causes the periodic variation of the pressure field around flaps and induces flaps to vibrate. The Angle between the flap and incoming flow changes periodically, causing the shedding vortices of flaps to be closer to the wall and enhanced. This would disturb the thermal boundary layer and bring the hot fluid near wall into the center of the channel. Thermal convection is thus enhanced significantly. We also found that increasing the number of flaps can improve the channel heat transfer performance, but it has a significant marginal effect and raise the pressure drop. For the proper spacing between flaps, a high Nusselt number, Colburn factor and highest thermal enhancement coefficient can be achieved in channel. Through the comparison of these physical quantities, the optimal layout is obtained. In the optimal layout, the combination modulation of the vortex-shedding frequency of cylinder and natural frequency of flap leads to the beat phenomenon of certain flaps. Thus, they vibrate more violently than the same flaps in other layouts.