Enhancement of heat transfer performance with asymmetrically inclined flexible vortex generators: a numerical analysis

Two-dimensional simulations are performed to investigate the effects of flexible vortex generators (FVGs) on thermal performance using the immersed boundary method to consider the fluid-structure interaction. The two FVGs are mounted on the upper and lower walls, respectively, with a symmetric arrangement. The asymmetric feature of the system is obtained by adjusting their inclination angles differently. The kinematics of FVGs are analyzed, revealing deflected and flapping modes depending on their inclination angles. The heat transfer system with the deflected mode of FVGs shows a decreased thermal performance as compared to that of the system without the FVGs. For the inclination angle greater than 0.5π, the FVGs show the flapping mode, and the thermal performance is observed to be improved by about 2 ~ 11% except for the cases where the inclination angles are identical. The enhancement of the thermal performance is stably reached by adopting asymmetric FVGs with inclination angles greater than 0.5π. The vorticity and temperature fields are analyzed in detail to elucidate the mechanisms through which the asymmetric FVGs improve thermal performance. By spectral analysis, the relations between the flapping kinematics of the FVGs, heat transfer, and energy loss are clarified.