Experimental Study of Turbulent Flow and Heat Transfer Behaviors Over a Micro-Rib-Dimple-Structured Surface

Abstract

An experimental study was conducted to characterize the evolution of turbulent boundary layer flow over a micro-rib-dimple-structured surface. In addition to measuring the surface pressure distribution and detailed flow field inside the dimple cavity, the heat transfer performance over the rib-dimpled surface was investigated using transient liquid crystal thermography. The flow field measurements were correlated with the heat transfer measurements to elucidate the underlying physical mechanism of the improvement in thermal efficiency due to the micro-rib structure. It was found that, compared to the dimpled surface, the micro-rib structure induces a stronger downwash flow and acts as a turbulator to enhance the turbulent mixing of the downstream flow, which significantly restricts the flow separation and the recirculating flow inside the dimple cavity. The dominant flows inside the dimple cavity are the downwash and successive upwash flows, which significantly enhance the turbulent mixing and, consequently, improve the heat transfer performance over the rib-dimpled surface. The measurements of the pressure loss and heat transfer performance indicated that the rib-dimpled surface has an overall thermal efficiency approximately 12–16% higher than that of the dimpled surface owing to the micro-rib structure.