The flow and heat transfer characteristics in a rectangular channel with miniature cuboid dimples

In present work, the miniature cuboid dimples are arranged in specified interval mode along spanwise direction at the bottom of a rectangular channel, and the depth of the miniature cuboid dimples is much less than the thickness of boundary layer. Large eddy simulation (LES) is employed to probe the flow behavior and heat transfer performance of the channel. The numerical results indicate that protrusion effect, secondary vortex, and local miniature air rolling bearing can be induced by miniature cuboid dimples, which result in the drag reduction and slight variation of heat transfer performance in rectangular channel. The simulation results reveal that the existence of the miniature dimples induces additional slip velocity, which effectively reduces the velocity gradient near the bottom of the channel. The low-speed streaks are widened and the mixing of high-speed and low-speed fluids is inhibited. The secondary vortex generated inside the miniature cuboid dimples increases the thickness of the viscous sub-layer, and the rolling friction between the vortex inside miniature cuboid dimples and the upper fluid above the miniature cuboid dimples replaces the sliding friction between wall and fluid. Compared with the channel without miniature cuboid dimples, more than 6% drag reduction can be obtained with the miniature cuboid dimples.