Fluid flow and heat transfer in a lid-driven cavity due to an oscillating thin fin: Transient behavior

A finite-volume-based computational study of transient laminar flow and heat (neglecting natural convection) within a lid-driven square cavity due to an oscillating fin is presented. The lid moves from left to right and a thin fin positioned perpendicular the right stationary wall oscillates in the horizontal direction. The length of the fin sinusoidally with its mean length and amplitude equal to 10 and 5 percent of the side the cavity, respectively. Two Reynolds numbers of 100 and 1000 for a Pr=1 fluid considered. For a given convection time scale (t(conv)), fin's oscillation periods (tau) selected in order to cover both slow (7/tcon > 1) andfiast (tau/t(conv) < 1) oscillation gimes. This corresponded to a Strouhal number range of 0.005 to 0.5. The number of cycles needed to reach the periodic state for the flow and thermal fields increases tau/t(conv) decreases for both Re numbers with the thermal field attaining the periodic later than the velocity field. The key feature of the transient evolution of the fluid flow the case with Re =1000 with slow oscillation is the creation, lateral motion and subsequent wall impingement of a CCW rotating vortex within the lower half of the cavity. CCW rotating vortex that has a lifetime of about 1.5tau brings about marked changes to the temperature field within a cycle. The dimensionless time for the mean Nusselt numbers reach their maximum or minimum is independent of the frequency of the fin's and is dependent on the distance between the oscillating fin and the respective wall, the direction of the primary CW rotating vortex. The phase lag angle between the oscillation of the fin and the mean Nusselt number on the four walls increases as the distance between the fin and the respective wall increases.