Research On Fluid Induced Vibration And Its Restraining Methods In Steam Turbine

Steam excited vibration becomes one of the key factors that affect the safe and stable operation of largescale steam turbines with high parameters and large capacity. Carrying out corresponding research on steam excited vibration and mastering its occurrence mechanism as well as suppression methods are of great theoretical significance and engineering value.The numerical analysis and experimental study of the flow field in seals is the base of steam excited vibration problem research. In this paper, a three dimensional model of the eccentric seal was setup using CFD method, and a transient method was applied to analyze the influence of different pressure ratio, rotating speed and eccentric ratio on the seal dynamic characteristics. Experimental study on the dynamic characteristics of the traditional labyrinth seal was carried out on the test bed of the rotor-bearing-seal system. The cylinder-seal system model was setup. In order to study the mechanism of steam excited vibration generated by seal, this paper analyzes the velocity and pressure distributions of seal. It shows that the reason of generation of flow induced force is the spiral flow induced by rotor rotating. There is generally an uneven distribution of the pressure field in the circumferential direction. The spiral fluid flow in seal cavities will result in a deviation of the highest pressure point from the smallest gap point, and this will generate a tangential force on the rotor. In this paper, the leakage performance and steam excited vibration forces of labyrinth seal is studied on the seal test rig, and the experimental results are compared with numerical calculation results.According to the mechanism of steam excited vibration in traditional axial seals, this paper proposed a new kind of radial embedded seal. Research and comparison of the seal performance between the traditional labyrinth seal and radial embedded seal were put forward using CFD method. The efficiency improvement and vibration reduction mechanism of the radial embedded seal was studied and the feasibility of engineering application was analysed. Compared with the traditional labyrinth seal, the radial embedded seal not only has better leakage performance, but also can cut off the spiral flows in seal cavities, and the ability resisting steam excited vibration was greatly improved. In addition, the wear resistance of the seal becames better due to the different directions between the rotor vibration and the seal gap variation.Inlet preswirl is a key factor affecting the stability of seal, and swirl brakes were the first proposed method to improve the stability of seal. In this paper, three typical seals including labyrinth seal, fully partitioned damper seal and hole-pattern seal were compared under three inlet conditions of no preswirl, preswirl and preswirl with swirl brakes. The results show that, for labyrinth seal the swirl brakes reverse the sign of effective damping at low frequency and improve seal stability performance in a wide frequency range. For fully partitioned damper seal and hole-pattern seal, the swirl brakes improve the stability performance by increasing the low frequency effective damping and reducing their crossover frequency. Installing swirl brakes effectively restrain the spiral flow and reduce the tangential force, and the stability of seal is improved.