Heat transfer augmentation due to flow pulsation in a channel with teardrop-shaped dimples investigated by large eddy simulation

This study investigated effects of flow pulsation on heat transfer performance of the surface with teardrop-shaped dimples. The flow structures and heat transfer characteristics were simulated by large eddy simulation with a Lagrangian dynamic sub-grid scale model. The cases of steady flow and pulsating flow (the Strouhal number of 0.3 and rms velocity amplitude normalized by bulk velocity of 0.14) were examined for dimple inclination angle of 30 deg, 45 deg, and 60 deg with in-line arrangements and for the bulk Reynolds number of 25,000. Surface-averaged results indicated that the flow pulsation increased the Nusselt number ratio by 9–12 %, the friction factor by 18–21 %, and the heat transfer efficiency index by 3–6 %. Using the phase-averaged results, it was clarified that the increased Nusselt number was due to the appearance and disappearance of flow-separation bubbles induced by the flow pulsation at the leading edge of inclined dimples and the time-averaged swirling flow intensity was well correlated with the surface-averaged Nusselt number and the friction factor.