大型水轮机顶盖动态特性数值模拟与试验研究

顶盖作为大型水轮机的主要承载部件,在实际运行过程中经常出现振动超标问题,严重威胁整个机组的安全运行。为此,从结构的动态特性出发,基于有限元法,建立了顶盖的高精度动力学仿真模型,采用Block Lanczo法求解得到前6阶固有频率,同步开展模态测试,可发现有限元计算结果与测试结果非常吻合,相同振型的固有频率最大误差仅为5.2%。接着开展工况振动测试,测得了顶盖工作时的径向和轴向最大振幅和振动频率,将此作为输入条件,基于动力学模型进行动力学响应分析,得到了振动状态下顶盖的结构应力。在此基础上,进一步进行谐响应分析,得到激励频率对结构应力的影响规律。结果表明,顶盖径向振动的危害远大于轴向振动,径向振动引起的振动应力为108 MPa,而轴向振动最大工况振动应力仅为36.7 MPa;振动应力随激励频率的变化出现宽幅波动,在81Hz附近,顶盖应力均存在明显应力尖峰值。

Numerical Simulation and Experimental Study on Dynamic Characteristics of Large Hydraulic Turbine Head Cover

As the main bearing component of large hydraulic turbines, the head cover is prone to excessive standard vibration in the actual operation process, which seriously threatens the operational safety of the entire unit. Therefore, this paper studies the influence of vibration on structural stress based on the dynamic characteristic analysis. A high-precision dynamic model of the head cover is established via the finite element method. The first six-order natural frequencies are obtained by Block Lanczo method, and corresponding modal test is carried out simultaneously to verify the simulation. The simulation results are in good agreement with the test results. The maximum natural frequency error is only 5.2%. Then, the radial and axial maximum vibration amplitude and frequency are measured by the vibration test under different working conditions. Taking maximum vibration as inputs, the dynamic response analysis is carried out to obtain the structural stress of the head cover based on the dynamic model. Results show that the damage of the radial vibration of the head cover is much greater than the axial vibration. The vibration stress caused by maximum radial vibration is 108 MPa, while the vibration stress at the maximum axial vibration is only 36.7 MPa. The vibration stress fluctuates widely with the change of the excitation frequency, and there are obvious stress peaks near 81 Hz.