Forced convective heat transfer over ribs at various separation

Flow over transverse ribs is a fundamental problem that has numerous applications in a range of scales from turbine cooling to urban roughness. It can be broadly divided into k-type or d-type flows exhibiting different characteristics. In this study, large-eddy simulation (LES) is used to examine the flows between two ribs at various separation and compare the local heat transfer coefficient (LHTC) on the cavity bottom. Flow instability initiates a dividing streamline at the leeward edge. In k-type flows, it reattaches at the cavity bottom that splits into a leeward recirculation and a windward redeveloping turbulent boundary layer (TBL). Heat removal from the recirculation and the redeveloping TBL is governed by intermittency and entrainment, respectively. Moreover, the dividing streamline impinges on the cavity bottom leading to a local maximum of LHTC. In d-type flows, the dividing streamline covers the cavity isolating the recirculation from the prevailing flow aloft. Heat is therefore solely removed by intermittency in which the LHTC increases monotonically from the leeward to the windward sides.