Effect of coolant mass flow rate of dirt purge hole on heat transfer and flow characteristics at a turbine blade tip underside

High thermal load on the turbine blade tip surface would lead to high temperature corrosion and severe structural damage. One method to reduce blade tip high thermal stress is to use cooler fluid from the compressor, that exists dirt purge hole mounted on the tip underside, for cooling purpose. In this study, internal serpentine cooling passage is modeled as a U bend channel with a sharp 180-deg turn with the dirt purge hole arranged at the tip-wall. The effect of the layout of dirt purge hole and varying coolant mass flow rate on flow structure, heat transfer on the tip-wall and friction factor of the U bend channel are numerically studied with Reynolds number ranging from 100,000 to 440,000. The results show that the vortex pair is forced to flow near the tip-wall while the increasing shearing effect induced by the vortex pairs increases the local heat transfer. With an increase mass flow rate of the dirt purge hole, the suction effect enhances the local heat transfer performance. However, the pressure loss is also increased accordingly at all Reynolds numbers. The augmentations with Reynold analogy performance and the thermal performance for 5.8% mass flow rate case is 12.5% and 12.7%, respectively, which reaches the highest performance augmentation compared to the smooth-tip channel.