Heat transfer characteristics of a circular cylinder covered by a porous layer undergoing vortex-induced vibration

Abstract

In this study, heat transfer characteristics of an elastically-mounted circular cylinder wrapped by a porous layer are studied numerically. The vibration of the cylinder is modeled as a forced mass-spring-damping system and it is assumed that the cylinder can move only in the transverse direction. The effects of Darcy number (10−6≤Da≤10−2), the dimensionless thickness of the porous layer (ep=0.25,0.5,1) and reduced velocity (3≤ur≤20) on the cylinder displacement, vortex shedding pattern, and Nusselt number are investigated. The Reynolds number, damping ratio, and mass ratio are taken as Re=150,ζ = 0.01 and mr=2, respectively. Results show that increasing Darcy number decreases the displacement amplitude of the cylinder. It is concluded that by increasing the reduced velocity from ur=3 to ur=9, the Nusselt number and the displacement amplitude of the cylinder increase and reach a maximum value at some optimum reduced velocity which depends on the value of Darcy number. Beyond which those quantities are reduced. It is observed that for all values of reduced velocity, the temperature distribution inside the porous layer is not affected by the position of the cylinder and the temperature variations are approximately equal at crest and rest points. Also, at low Darcy numbers, the temperature distributions are uniform in the peripheral direction due to small flow penetration into the porous material Moreover, at Da=10−2,10−3 and 10−4 the Nusselt number is increased by 7%, 9% and 10% for the reduced velocities of ur=7,ur=3 and ur=6, respectively.