Numerical Study On The Influence Of Casing Air Injection On The Leakage Flow At The Top Of Turbine Blade

Gas turbine is a high-speed rotating internal combustion engine driven by continuous flow of gas.It transforms the energy of fuel into useful internal mechanical energy,and plays an important role in various industrial fields.Because of the flow characteristics,the main flow will produce leakage flow when flow through the tip clearance area.Leakage flow will cause large flow loss,reduce the output po-wer of the gas turbine,and also cause serious thermal damage to the blade tip and shorten the service life of the gas turbine.Therefore,it is of great significance to study the mechanism of leakage flow and reduce its influence.In this paper,the concept of shroud injection is added to the tip clearance area,and the effect of casing air injection on tip leakage flow is studied by numerical simulation.Firstly,the models of the tip of the squealer blade and the wall of the turbine are established,and the SST k-co turbulence model is selected.The flow characteristics in the area of the tip of the squealer blade are studied by numerical calculation.By comparing the heat transfer coefficient of the blade tip,the distribution of velocity and streamline,the cooling coefficient of the section,the Mach number,the surface limit streamline and the total pressure loss coefficient under different blowing ratio,the influence of blowing ratio on the tip leakage flow is obtained.The results show that the addition of blowing ratio can reduce the loss of passage vortex at the blade hub,but increase the loss range of passage vortex at the blade tip along the blade height.The increase of blowing ratio can effectively improve the high temperature distribution of the casing wall and the cooling efficiency of the whole squealer.But the change of leakage flow is not consistent with the change of blowing ratio.When the blowing ratio increases from 0 to 1.0,the vortex in suction side of the blade is increased.When the blowing ratio is increased to 2.0,the leakage vortex in the original position will disappear completely and form new leakage vortex in the rear area under the suppression of the casing air injection from the wall.Secondly,the same research method is used to study the steady simulation results of the tip leakage flow at different relative translation speeds.The results show that the larger the translational velocity is,the larger quantities of the leakage vortex on the suction side is,the smaller the diffusion range of the leakage vortex is,but it can't be disappeared.The addition of translational motion will squeeze the whole flow field,making the secondary reattachment vortex line appear on the suction side surface.The increase of translational velocity will make the leakage vortex mixed with the passage vortex on the top of the blade,and the flow loss will spread to 50%to 96%of blade height.Finally,large eddy simulation(LES)is used to study the unsteady flow field under different blowing ratio and translation speed.Through the analysis of the unsteady cloud chart and spectrum chart,the conclusion is as follows.In the tip region,the main effect of the change of blowing ratio is concentrated in the area under the coolant hole and the leading edge of the blade tip.However,the translational motion has a great influence on the top region of suction side blade and the area directly below the coolant hole of casing wall.When the blowing ratio is between 0-2,the flow loss of the outlet vortex system can not be reduced obviously due to the addition of its own mass flow.However,with the increase of the relative translation velocity,the flow loss of the leakage vortex will be reduced,but the interaction of the whole flow field will be intensified,leading to the increase of the flow loss of the main flow.