Investigation On Mechanism Of Leading Edge Fillet In Turbine Blade

With the increase of the turbine inlet gas temperature, the study on the thermal control of turbine vane endwall has become more and more important. It has been proved that it is effective to pre-cool the vane endwall surface by leading edge fillet before film cooling is used.So far, the mechanism of leading edge fillet is still unclear. Besides, the current study has been carried out under the conditions of low Mach number and low free-stream turbulence intensity, thus the results are less instructive in the real application to the turbomachinery.In this paper, the turbine vane in the high pressure stage of a gas turbine working on the ground was used as the baseline. Firstly, the numerical simulation was performed under different cascade exit Mach numbers, such as 0.6, 0.85 and 1.1. The numerical results were compared with the experimental ones. Secondly, four configurations of leading fillets were designed and then investigated under the free-stream turbulence intensity 20.4% and the cascade exit Mach number 1.1. Thirdly, a better leading edge fillet structure was selected and simulated numerically under the free-stream turbulence intensity 20.4% and different cascade exit Mach numbers, e.g. 0.6, 0.85 and 1.1, in order to reveal the effect of the leading edge fillet on the wall temperature reduction on the vane surface and on the flow condition improvement.The results show that the main area influenced by the fillet is from the endwall to 25% of the blade height, i.e. the spanwise immersion of the fillet, where the area with the highest temperature reduces significantly, and meanwhile the area with the lowest temperature enlarges. The flow accelerates upwards along the fillet surface, which eliminates the horseshoe vortex developed in the corner between the leading edge and the hub. The leading edge fillet has significant effects on the elimination of the passage vortex. Based on the observation of the energy loss distribution at the exit of the cascade, it can be seen that the leading edge fillet redistributes the energy loss in the spanwise direction, resulting in the reduction in energy loss in the hub region.The size of leading edge fillet has a significant influence on the reduction in wall temperature and in energy loss according to the comparison between the simulation results of different leading edge fillet configurations. As the size of the fillet increases, the reduction in area with the highest temperature also rises, and the effect on the energy loss reduction is more significant. Within the area above the leading edge fillet, a bigger fillet results in a larger reduction in energy loss, while a smaller fillet has little effect on the energy loss reduction, or even enhances the energy loss.The results of the same leading edge fillet working under different Mach numbers at the cascade exit show that when the Mach number at the cascade exit is high, the effect of the fillet on the reduction in wall temperature is more obvious. When the Mach number at the cascade exit is greater than 1.0, the area with the highest temperature on the vane hub decreases more significant. Since the passage vortex only occurs in the baseline turbine cascade when the Mach number at the cascade exit is greater than 1.0, while it does not happens in the fillet cascade, it infers that the fillet has a more significant effect on the flow field improvement under a high cascade exit Mach number. When the Mach number at the cascade exit is smaller than 1.0, the energy loss within the area above the leading edge fillet increases in comparison with that of the baseline turbine cascade.In order to achieve the aim of reducing the wall temperature, the energy loss through the leading edge fillet, it should be designed under its working conditions.