On flow vortices and tip heat transfer in a ribbed two-pass channel with various rib angles

Purpose This study focuses on the internal tip heat transfer and how it is affected. The tip area of a turbine blade is a highly vulnerable region, and understanding the flow and heat transfer performance (HTP) of the internal serpentine channel is one of the key factors in improving the cooling effect at the tip of blade. Most research focused on the sidewalls of serpentine passages (representing the pressure surface and suction surface of blades), while neglecting their impact on the internal tip heat transfer. Design/methodology/approach Four differently angled channel ribs (0°, 30°, 45° and 60°) and straight parallel tip ribs of a two-pass channel are investigated. The inlet Reynolds numbers are 10,000, 15,000, 25,000, 35,000 and 50,000, respectively. Findings The results indicate that the transverse vortices induced by the straight parallel channel ribs can promote the evolution of the Dean vortices in the turning region, thereby enhancing the tip HTP by almost 14.8%. The longitudinal-like vortex induced by inclined parallel channel ribs enhances the HTP on the pressure/suction surface of the blade, but suppresses the evolution of the Dean vortex, thereby inhibiting tip heat transfer. Tip straight ribs in a 60° inclined ribbed two-pass channel under static and rotating conditions can effectively promote the cooling effect of the blades, and the corresponding HTP (tip surface, pressure surface and suction surface) can be improved by up to 17.4%. Practical implications The numerical results can be used for the internal cooling channels of turbine blades. Originality/value This work takes the ribbed serpentine cooling channel as the research object, with focus on analysis of the HTP mechanism of the tip and sidewalls, and it also provides measures to increase the HTP of the tip.