Loss Mechanism Research And Experiment On Medium-pressure Cascade Ofa Steam Turbine

The development of high-power turbine units is of great significance for achieving the national strategic goals of energy-saving and emission reduction and mitigating the energy crisis.The design and adoption of high-performance advanced blades is an essential means for the efficient operation of steam turbines.For this reason,this paper studied and verified the blade aerodynamic performances of vane blade changing incidence angle and changing Mach number through a fan blade cascade test and numerical calculation methods on a certain medium-pressure stage of a high-power steam turbine.At the same time,the characteristics and concepts of blade design are summarized by means of parametric methods.First of all,the results show that in this experimental stage,the roots and the tops are all post-loaded leaf shapes under test conditions,which is conducive to the control of the lateral secondary flow strength of the end walls;Although the middle leaf type is also post-loaded,the axial position of the lowest pressure point on the suction side has different degrees of advancement with respect to the root and the top,besides,the load on the middle leaf is obviously increased.The combination of the two achieves the dual goals of high blade load and high efficiency.With the change of the incidence angle from-10° to +10°,the total flow loss of the cascade is between 3.22% and 4.17%,and it reaches the minimum near the-7°angle of attack.Under the test conditions,the variation of the loss coefficient is within 1%,indicating that the characteristics of the blade's variation in the angle of attack is good.Secondly,the numerical calculation results show that the calculation results of the variation angle of attack and the experimental results basically fit together,and the comparison between the two verifies the accuracy of the test results and the credibility of the calculation results.From the results of the Mach number calculation,it can be seen that during the Mach number changing from 0.2 to 0.8,the position of the lowest pressure point on the suction side of the cross-section has obviously shifted back.The post-loading characteristics of the blade shape have increased,and the blade load has also decreased significantly.As the Mach number increases,the cascade flow loss decreases first and then increases.The total flow loss value reaches the minimum around 0.6Ma.Finally,the NUMECA Auto Blade is used to parameterize and extract the two setsof stationary blades in the medium and high pressure stages.Based on the results of the previous analysis,it was found that the blade designers used high-loaded airfoil on medium-pressure blades.And the leaf design load coefficient was generally above 0.75 and was significantly higher than that of high-pressure blades.At the same time,positive curving of the blade will reduce the load on both ends of the three-dimensional blade and increase the load in the middle.The larger the angle is and the thinner the blade is,the more obvious the magnitude of this load change.In addition,the variation of the load in the direction of the leaf height caused by the positive curving of the blade is more pronounced in the medium-pressure-stage with a large camber angle than that in the high-pressure stage with the small camber angle.