Local heat/mass transfer distributions on the bottom surface of a cavity exposed to an approaching turbulent boundary layer: Aspect ratio effects

We investigate convective transport from the bottom surface of rectangular cavities of depth d exposed to an oncoming boundary layer flow, using experimental and numerical techniques. The effects of cavity width W are explored for cavities with different lengths L in the downstream direction. Depending on the value of L/d (0.52≤L/d≤10), the approaching boundary layer separates and reattach on the bottom surface and establish a new boundary layer, or skims past the open face of the cavity. This results in significantly different convective transport coefficient distributions on the bottom surface. As cavity width is reduced, three-dimensional effects arise, with interaction of vortex systems on the cavity floor. Detailed spatial distributions of the transport coefficient are captured using a mass transfer technique based on naphthalene sublimation. Further insight into the flow structure responsible for the observed distributions is gained through numerical simulations using a k−ω SST model that is first validated using the experimental results by using a heat/mass transfer analogy factor. Flow streamlines from the computations are used to explain how the time averaged streamlines affect the heat transfer at the bottom surface.