Numerical Study On The Influence Of Tip Clearance On Turbine Performance

The existence of the blade tip clearance has a great influence on the performance of the turbine and the flow field of the blade passage,so the research on the flow characteristics of the tip leakage flow is very important to improve the performance of the turbine.Current research generally considered,the performance of the turbine,the structure and size of the leakage vortex,and the unsteady characteristics of the turbine flow field will be changed when the tip clearance height changes.However,in the actual working environment of the turbine blade,there are effects of high temperature gas and the high centrifugal force caused by the high speed of the rotor blades,so the deformation of the blade is caused,therefore,the change of the gap height is caused by the deformation of the blade,and then the flow field in the gap region is changed too.The in-depth study of the low pressure turbine tip clearance was calculated by numerical method in this paper,the structural characteristics of the turbine blade,disc and the casing are analyzed by using WORKBENCH platform.The numerical simulation of the three stage turbine with different tip clearance height is carried out by using CFX.Finally,the aerodynamic performance of the turbine is compared.It is found that the temperature and centrifugal force is the most important factor affecting the radial deformation of the blade,the disc and the casing.With the tip height increases,the performance of the turbine becomes worse,and the interaction between the leakage vortex and the passage vortex will be enhanced.In the design condition,the leakage vortex is relatively stable,and the wake interference is the main factor of unsteady flow in the flow field.With the decrease of flow rate,the flow instability oscillation becomes the dominant factor.However,when the tip height is different,the influence of unsteady fluctuation on each flow condition is also different.