Investigation Of Aerodynamic Performance And Heat Transfer For Cavity-Tip Turbine Cascade

Modern gas turbines operate in high temperature and high pressure in a long period,which puts a severe test on turbine materials,cooling efficiency and heat transfer control.In order to avoid the friction between the blade and the casing,a gap of 1%-2%of the blade height usually exists between the blade tip and the casing.Due to the pressure difference on both sides of the gap,the fluid will flow into suction side and form the leakage vortex,the velocity of the leakage flow is high,and the boundary layer of the leakage flow is thin,which will create large mixing loss and high heat transfer coefficient in the tip of the blade,and bring about bad aerodynamic performance and heat transfer characteristics of the turbine.Therefore,it is necessary to analyze the characteristics of flow and heat transfer and find out the high loss and high heat exchange area and then control it properly.Based on the FLUENT software,this paper used the numerical simulation method to analyze the influence of the tip geometry on the leakage flow and the heat transfer phenomenon.Firstly,the performance parameters of the turbine blade tip under different width of winglet was studied.The results show that with the increase of the width of winglet,both driving pressure difference on two sides of the blade tip and the total pressure loss coefficient of the leakage vortex core all decrease,and the average heat transfer of blade tip decreases too.However,the leakage mass flow rate remains unchanged.Then,the effects of five different tip structures on aerodynamic performance and heat transfer characteristics of turbines were analyzed.It is found that the cavity blade and squealer blade form the background step vortex,the cavity vortex and the leakage vortex at the tip,among which the background step vortex can significantly reduce the leakage flow rate and the total pressure loss coefficient of the outlet.The groove vortex will increase the local maximum heat transfer coefficient of the tip,and the leakage vortex will cause serious total pressure loss.Finally,the effects of the height and width of squealer on the flow and heat transfer performances at the tip were studied.It is found that increasing the height of the squealer can significantly enhance the background step vortex and the cavity vortex,and increasing the height of squealer within a certain range will reduce the total outlet pressure loss coefficient and the leakage mass flow rate.However,when the squealer increases to a certain height,the leakage mass flow rate remains unchanged,and the local highest heat transfer coefficient of the tip increases first and then decreases with the increase of the squealer height.Increasing the squealer width will weaken the background step vortex and the cavity vortex strength.As the squealer width increases,the tip leakage mass flow increases,the total pressure loss coefficient of outlet remains unchanged,and the local highest heat transfer coefficient of the tip decreases.