基于谐响应工业汽轮机调节级动应力分析研究

Research on Dynamic Stress of Regulating Stage of Industrial Steam Turbine Based on Harmonic Response

数值计算部分进汽、变转速工业汽轮机调节级动应力,讨论转速对其影响。某高温高压工业汽轮机,转速变化范围7200r/min~11000r/min。分析结果表明最低转速的等Q准则涡面积较最高转速增加17%~23%,同时部分进汽产生的低频冲击力也增加7%~16%。将瞬态汽流力傅里叶分解为若干简谐激振力之和,然后使用ANSYS计算循环对称盘片结构在这些简谐力下的响应,因各节径振动之间具有正交性,将以上响应叠加就可以得到整个盘片瞬态动应力,这样不仅节约计算资源而且结果更精确。判断哪些转速会产生较大的动应力可以有效减少计算量,一般危险转速为最低转速和可发生节径共振的转速。高频频激振力虽小,若其满足盘片系统共振条件,所产生的破坏要比部分进汽低频激振力大。所分析的调节级最大动应力对应的转速为最低转速7200r/min,其应力变化幅度是最高转速的120%,叶根销孔处动应力最大,也最容易失效,从时间上看,最大动应力出现在叶片从进汽弧段进入堵塞弧段这一时刻,设计工业汽轮机调节时应避免盘片在转速范围发生与喷嘴当量只数相同倍频的共振,同时要注意优化喷嘴弧段分布以减少动应力。

Numerically calculate the dynamic stress of the regulating stage of industrial steam turbine with variable speed of steam and partial inlet,and discuss the influence of speed.The speed of a high temperature and high pressure industrial steam turbine variates from 7200 to 11000r/min.The analysis results show that the iso-Q-criterion vortex area at the lowest speed increases by 17%~23%compared with the highest speed,and the impact force generated by partial inlet also increases by 7%~16%.The transient steam flow force is decomposed into the sum of several simple harmonic excitation forces,and then the response of the circular symmetric blade-disk structure under these simple harmonic forces is calculated using ANSYS.Because the vibration of each nodal diameter is orthogonal,the transient dynamic stress of the entire blade-disk can be obtained by superposition of the above responses,which not only saves computing resources but also results more accurately.Determining which rotational speeds will generate larger dynamic stress can effectively reduce the amount of calculation.The dangerous rotational speed is the minimum rotational speed and the rotational speed at which the resonance can occur.Although the HEO(high engine excitation order)force is small,if it meets the resonance conditions of the blade-disc system,the damage may be greater than the LEO force generated by partial inlet.The speed corresponding to the maximum dynamic stress in this paper is the minimum speed of 7200 r/min,its variation range is 120%of the maximum speed.The maximum dynamic stress at the blade root pin hole is also the most likely to fail.From the perspective of time,the maximum dynamic stress occurs at the moment when the blade enters the blocking arc from the inlet arc segment.When designing the industrial turbine regulation,it is necessary to avoid the disk resonance with the same frequency multiplication as the nozzle equivalent in the speed range.It is also necessary to optimize the distribution of the nozzle arc segment to reduce the dynamic stress.