Influence Of Turbine Tip Structure And Cold Air Injection On Tip Loss And Heat Transfer

In order to prevent the friction between the rotor blade and the stationary casing in the passage of aero-engine gas turbine,a certain radial clearance is usually set between the rotor blade and the stationary casing.The existence of tip clearance will seriously affect the overall performance of the engine.The pressure side air flow will form tip high temperature leakage flow driven by tip load through the tip clearance,this means that the blade,especially the tip part,will bear higher heat load,which will easily cause the oxidation and ablation of the tip area,leading to the decrease of aerodynamic performance,the increase of channel loss and even the failure of the blade performance.Therefore,it is very important to effectively suppress the tip leakage flow and efficiently cool the tip for the efficient and stable operation of the turbine components and the whole power plant.Under the operation condition of turbine,the tip clearance size will have a certain impact on the efficiency of rotor blade due to the combined effect of centrifugal force,thermal stress and aerodynamic force.Therefore,this paper first carries on the numerical simulation calculation to the plane blade tip under different clearance sizes,and gives the specific parameter settings.The traditional rib tip is widely used in turbine rotor blade because it can effectively control the tip leakage flow,so this paper attempts to improve the rib tip structure to further reduce the aerodynamic loss of cascade.Next,the influence of rib width to height ratio on the flow field and performance of the blade tip without cooling ribs is explored.Finally,in order to find the law of leakage flow and flow heat transfer in turbine rotor blade with cooling jet,the influence of film hole position on tip flow and cooling was studied by numerical simulation.The leakage flow field,leakage flow rate,leakage loss,surface heat transfer coefficient and tip film cooling efficiency were analyzed in detail,so as to obtain lower cascade aerodynamic loss and better relative performance of turbine blades.The results show that increasing the gap size of the blade tip is not conducive to the suppression of leakage vortex and the control of leakage flow.The total aerodynamic loss of cascade is higher,the total aerodynamic pressure loss of the tip of the rib on the pressure side is basically the same as that of the tip of the whole rib.The control effect of the tip of the rib on the pressure side is the best,but it is not conducive to the control of the leakage flow in the gap,But the tip of the upper channel will increase,and the tip of the rib on the suction side has the best effect on the leakage flow control.However,the leakage vortex loss is the highest,and some rib tip has the best width height ratio,The results show that the total loss at the exit of the blade tip increases with the addition of cold air injection,but the proportion of the cold air flow to the total flow is small,so the increase of the total loss caused by cold air is not obvious.Although the blade tip with the middle arc hole at the bottom can reduce the energy loss of the blade,it will increase the relative leakage flow,On the other hand,the suction side rib notch tip not only reduces the total energy loss,but also reduces the leakage flow.