Flow structures and heat transfer on small-scale concentric ribs rough surface for confined turbulent jet impingement

Abstract

The concentric ribs of the surface for round jet impingement heat transfer are investigated at a low nozzle-plate spacing of 2 with Reynolds number Re = 23,000. To study the effect of small roughness and roughness types to the characteristics of flow structures and heat transfer, different ratios of pitch-to-height p/e are chosen. First, a shear stress transport (SST) with transition model is performed and validated for smooth and rough cases, which shows superior performance for jet impingement. Then, the evolution and the effect of different roughness types in heat transfer and flow fields are studied. It is found that how many recirculation zones in one cavity depend on p/e. But changes mainly occur in the transition region, which reflects the role of rib to the flow instabilities. This phenomenon contributes to the change of peaks of the local maximum heat transfer. For a large pitch, it seems that the ribs make the flow transition premature, leading to a monotonic decrease of local maximum heat transfer. Meanwhile, the rib roughness shows blockage to the flow. For small p/e, the effect of blockage becomes stronger than that for larger p/e, leading to a lower heat transfer rate.