Influence Of Dimple On Aerodynamic Performance Of Transonic Turbine Cascades

In the era of great development of aviation technology,high-load turbines play an important role in aero-engines.However,with the increase of load,larger scale separation is brought about,which limits turbine performance.Research on turbine cascades is the core of turbine aerodynamic performance.The flow situation at the turbine cascade root is complex and the secondary flow loss at the endwall is serious.Therefore,the control of flow loss on the turbine surface has become the focus of research.Firstly,the 1+1/2 high-pressure stage contra-rotating turbine cascade was selected as the research object,and the loss structure of the cascade is calculated and analyzed.The results show that the flow loss in the cascade passage mainly includes the angular vortex loss caused by the accumulation of low-energy fluid in the corner area and the wake loss caused by the trailing edge of the blade.Secondly,the mechanism of the dimple to reduce cascade loss is analyzed.It is found that the airflow flowing through the dimple will generate a small vortex inside the dimple,which can mix the high-energy fluids in the main flow area into the boundary layer and increase the kinetic energy of the low-energy fluids.In addition,it is precisely because of the vortex inside the dimple that the original gas-solid contact turns into gas-gas contact,which reduces the friction resistance,that is,plays the role of "rolling bearing".Then,spherical dimples were placed on the blade surface/end wall and the dimple parameters were changed.Dimple design has a lot of freedom,including depth,location,number and so on.Different parameters in dimple will have any effect on turbine cascade loss characteristics,the analysis found in the separation line before,proper depth and the number of dimples array can effectively control the three dimensional separation Angle area,able to get a better effect of impairment,up to a 3.90% reduction in total pressure loss coefficient,but the existence of the dimples at the same time will increase the fluid disturbance,increase the friction loss of fluid itself.Finally,the two optimal dimple schemes were selected to explore the variable working conditions,and the distribution of total pressure loss at the outlet section,the change of turbulent kinetic energy level and the distribution of static pressure on the blade surface were obtained by numerical simulation.The analysis showed that the dimple could effectively reduce the cascade loss at a relatively high pressure ratio,and the specific reasons needed to be further verified.