Heat transfer enhancement in a rectangular channel with flow-induced pitching, heaving or surging of an airfoil

Abstract

This paper presents a numerical investigation of the flow-induced pitching, heaving or surging of an airfoil in a rectangular channel for heat transfer enhancement. The flow dynamics, airfoil fluttering response, and heat transfer performance are analyzed and discussed at four different Reynolds numbers (Re = 700, 1000, 1300 and 1500), three rotational axis locations (ax/C=0.25, 0.33 and 0.42), two airfoil perturbation modes (passive vs. active), and three combinations of multiple airfoil freedoms (pitch only, pitch and heave, and pitch and surge) with various stiffness coefficients. It is found that after Reynolds number reaches 1000, the pitch only airfoil starts the similar self-fluttering pattern, and the fluttering effect becomes the dominant influencer for increasing the Nusselt number compared to the Reynolds number effect. Placing the rotational axis at ax/C=0.42 achieves the highest thermal enhancement factor η of 1.4, while when ax/C=0.25, the airfoil oscillation diminish effect is vast because of its aerodynamic center. The passive pitching airfoil can achieve more than 6% of the thermal enhancement factor than the active ones. Adding another heave or surge degree of freedom to the pitching airfoil, the heat transfer enhancement of the channel can also be improved. The present work can facilitate future optimizations of airfoil-based flow-structure interaction system for heat exchanger channels.