The current study explores the possibility of using the coolant injected from the near tip suction side of a turbine blade to reduce the tip leakage loss. Each case studied has a cooling hole injecting a coolant stream. To model the mixing of the coolant at different axial locations, each of four cases is investigated with a cooling hole located at 10% blade axial chord [Formula: see text], 20% [Formula: see text], 30% [Formula: see text] or 40% [Formula: see text] from the leading edge. In computational fluid dynamics simulation, the exit area of the cooling hole is defined with mass flow inlet boundary condition to simulate a coolant injection. It is found that the tip leakage loss of the case with a cooling hole located at 10% [Formula: see text] is the lowest and is 3.2% lower than that of the uncooled baseline case. The tip leakage loss increases as the cooling hole located further downstream. For the case with cooling hole at 40% [Formula: see text], the loss is 1.5% higher than the uncooled baseline case. The effect of the blowing ratio on the tip leakage loss is also investigated. For the case with the cooling hole located at 10% [Formula: see text], the tip leakage loss first decreases and then increases as the blowing ratio increases. When the tip leakage loss of one case is less than that of baseline case, it is found that mixing of the coolant and the low-energy fluid in the tip leakage vortex core reduces the stagnation pressure difference between mainstream and the fluid within the vortex core, and thus reducing the mixing loss within the blade passage.

Controlling the tip leakage flow is crucial for improving the aerodynamic and thermal performance of unshrouded highpressure turbines. The advantages of a single cooling hole to release coolant from suction surface were sought by numerical method in the cases of flat tip blade. Compared with no coolant case, the coolant cases exhibited significant differences on the intensity and evolution of tip leakage vortex and corresponding aero-thermal performance of turbine depending on locations to release coolant and blowing ratios of coolant. The impact of five axial locations to release coolant, namely 10%, 20%, 30%, 40%, and 50% axial chord of blade respectively, was studied. And the impact of three blowing ratios of coolant, namely 0.7, 1.4, and 2.1, was investigated. Within the scope of the current study, the best aerodynamic effect was achieved when the coolant was released before 30% axial chord of blade. The aerodynamic effect became worse when the coolant was released after that place. This phenomenon implied that it was a better strategy to release coolant at the initial period of evolution of tip leakage vortex. With regard to the cases with coolant released at 20% axial chord of blade, the mixed-out loss caused by tip leakage vortex reduced with the increasing of blowing ratio from 0.7 to 2.1. Last but not least, the thermal performance of suction surface of blade was improved with the increasing of blowing ratio.