低压缸零出力供热工况中低压缸连通管内部流动数值模拟

Numerical simulation of internal flow in connecting pipe of IP and LP cylinder under zero-output heating conditions of LP cylinder

对低压缸零出力技术改造后的某300 MW供热汽轮机组中低压缸连通管、连通管液控蝶阀、采暖抽汽管道、冷却蒸汽旁路、冷却蒸汽流量孔板和冷却蒸汽调节阀等根据实际尺寸建立三维模型,并进行网格划分;并采用Realizable k-ε模型和Scalable壁面函数法进行不同供热工况下中低压缸连通管及冷却蒸汽旁路内部流动数值模拟。模拟结果表明:中低压缸连通管及冷却蒸汽旁路系统复杂结构会使蒸汽流动产生分离,使整个管路系统内流动不稳定,低压缸进汽口流动不均匀;低压缸零出力工况,蒸汽在冷却蒸汽调节阀出口扩张段会产生超音速,并在其后连接的弯头处产生强激波和马赫盘。模拟结果反映了汽轮机抽汽供热及低压缸零出力工况中低压缸连通管内较复杂的蒸汽流场和状态,为后续技术改造的方向提供了理论依据。

For a 300 MW heat supply steam turbine unit after retrofitting with zero-output technology of low pressure(LP)cylinder,a three-dimensional model is established and meshed according to the actual dimensions of the connecting pipe of intermedium pressure(IP)and LP cylinder,the hydraulic control butterfly valve of the connecting pipe,the heating steam extraction pipe,the cooling steam bypass,the cooling steam flow orifice and the cooling steam control valve.The Realizable k-εmodel and Scalable wall function method are used to carry out numerical simulation for the internal flow of the connecting pipes and the cooling steam bypass under different heating conditions.The simulation results show that,the complex strucutre of the connecting pipe of IP and LP cylinder and the cooling steam bypass system will separate the steam flow,making the flow in the whole pipeline system unstable and the flow at inlet of the LP cylinder uneven.Under zero output conditions of the LP cylinder,the steam will reach supersonic speed in expansion section at outlet of the cooling steam regulating valve and produce strong shock and Mach disk at the subsequent connected elbow.The simulation results reflect the complex steam flow field and state in the connecting pipe of IP and LP cylinder under zero output conditions of the LP cylinder,which provides a theoretical basis for the direction of the subsequent technical transformation.