Strength Optimization Of Governing Stage Blade Of Small Back Pressure Turbine With Wide Load Range For Cogeneration

As a large rotating equipment,turbine has a wide range of applications in industry,and as the core component,the blade decides whether the turbine can run safely and stably.As the first working stage of steam turbine,the governing stage is in the worst environment with the highest pressure and temperature.The governing stage blades are subjected to high pressure difference,high enthalpy drop,high impact,and exciting force and thermal stress caused by partial steam intake,etc.,and the working environment is more complex than all other pressure levels,which is more prone to accidents.In this paper,the governing stage blades of a small back pressure steam turbine in a cogeneration of heat and power plant are taken as the research object to investigate the stress conditions of the turbine in a wide range of load changes.The stress components are found out through the force analysis of the governing stage blade,and centrifugal tensile stress,centrifugal bending stress and steam bending stress are emphasized.Based on the theoretical analysis of static strength,the mechanical calculation model is established and the calculation formula of the above stress is obtained.The1-1 section at the bottom of the blade profile and the 2-2 section at the neck of the blade root were determined as dangerous sections.The stresses of the inlet edge,outlet edge,back arc of the 1-1 section and point A,B,C,D of the 2-2 section can be calculated using the thermodynamic calculation software Axturbo and the three-dimensional software SolidWorks,and the defects in the strength design of the initial blade are found out.Through the analysis of the force influencing factors of the regulating stage blade,the blade was optimized from two aspects of blade structure and operation mode respectively.The rhomboid blade is used to replace the arc blade,and the sliding pressure operation is used to replace the constant pressure operation.It is concluded that the rhomboid blade sliding pressure operation is the best scheme by comparing each scheme.Based on the finite element analysis method,the blade strength in the above optimization scheme was checked by the finite element software ANSYS Workbench.The stress of the blade is investigated from the average stress of the cross section and the stress concentration of the blade root.The results are consistent with the theoretical calculation,and the stress condition of the rhomboid blade is the best when the blade is operated under sliding pressure.In addition,the modal calculation of arc blade and rhombus blade is carried out using Workbench.According to the results,the avoidance rates of low frequency excitation and high frequency excitation of the two blades meet the requirements of the specification,and these two forms of blade are safe enough from the point of view of vibration.