Mechanical Characteristics Analysis Of Steam Turbine Low Pressure Outer Casing Based On Thermal-fluid-solid Coupling

As one of the important structural components of the steam turbine,the(LP)Low Pressure outer casing not only ensures the safety and stability of the unit during operation,but also has a greater impact on the economy of the unit.With the development of high-parameter and high-power steam turbine units,the size of the LP outer casing is also increasing with the increase of the steam flow-rate,which puts forward higher requirements for the adaptability and structural reliability of the LP outer casing.At the same time,due to the great changes of energy structure in recent years,a large number of existed steam turbine units have been operating under low load for a long time due to the requirements of grid regulation,which not only increases the internal flow loss of the LP outer casing,but also results in complex structural mechanics,which affects the stable and safe operation of the unit.How to reduce the steam flow loss,improve the thermal efficiency of the unit and the stability of operation under different working conditions on the premise of ensuring the mechanical properties of the casing has become the key technology for the optimization design and transformation of LP outer casing.This paper combined with the Deyang Open Industry-University-Research Cooperation Special Fund Project-"350MW Steam Turbine LP Outer Casing Structure and Flow Design Key Technology Research and Development" to explore the calculation and analysis method of the mechanical characteristics of the LP outer casing based on thermal-fluid-solid coupling,which can accurately predict and analyze the internal flow field and structural mechanical characteristics of the LP outer casing,laying a certain technical foundation for the flow design and structural design of the LP outer casing of the steam turbine.At the same time,it also provides technical means to analyze the deformation and vibration problems of LP outer casing of steam turbine in the existed power plant,the main contents and conclusions are as follows:(1)Research the influence of different working condition parameters on the flow and temperature distribution of the LP outer casing.The numerical simulation method is used to analyze the internal flow field and temperature field of the LP outer casing,and the influencing factors and distribution law of the flow energy loss in the LP outer casing under design conditions and small flow and high back pressure conditions are studied.The results show that the total pressure in the LP outer casing flow field gradually decreases from the top to the bottom of the casing,and along with the generation,growth,collapse and regeneration of the channel vortex,the support components increase the internal flow loss.The aerodynamic performance of the LP outer casing is significantly reduced under small flow and high back pressure conditions,the steam temperature distribution in the casing is more uniform,and the temperature of the inner casing has little effect on the steam temperature.(2)Research the numerical simulation method of the structural statics characteristics of the LP outer casing under multi-field coupling.The thermal-fluid-solid coupling method is used to conduct static analysis of the LP outer casing structure,and the deformation law of LP outer casing structure under gravity,pressure and temperature load is obtained.The results show that the LP outer casing has high structural reliability,and the stiffness of the upper half of the casing is significantly lower than that of the lower half.Under design conditions,the deformation of the LP outer casing due to vacuum load is more obvious;steam temperature is the main factor in the deformation of casing under the conditions of small flow and high back pressure.(3)Research the dynamic analysis of the LP outer casing structure,and master the vibration characteristics of the casing.The results show that,without considering the damping of the support system,the inherent frequency of the LP outer casing of a 350 MW steam turbine is similar to the operating frequency of the unit,and the upper half-casing inclined stiffener plate and the lower half-casing support plate vibrate more obviously.Under the design conditions,the vibration deformation on the bearing box of the LP outer casing is small,and the vibration mode is mainly horizontal swing;under the condition of small flow and high back pressure,the vibration at the bearing box is relatively large,which will affect the normal operation of the unit.Therefore,the LP outer casing needs to be further optimized during the transformation of the unit.This paper analyzes the mechanical characteristics of the LP outer casing under the thermal-fluid-solid coupling effect,which can more accurately simulate the changes in the mechanical properties of the LP outer casing under different working conditions.The result can been used to guide the structural design of the LP outer casing and the optimization of the unit,and has certain engineering application significance.