Dynamic characteristics coupled thermal and dynamic loads for labyrinth seal in ultra-supercritical steam turbine

The operating safety of ultra-supercritical steam turbine is seriously affected by steam flow excited vibration in labyrinth seal. The DEFINE_CG_MOTION and DEFINE_PROFILE control macro were used to establish rotor whirl equation. The deformation of seal teeth under thermal and dynamic loads was calculated by Workbench fluid-solid coupling method. So the operating dynamic characteristics in seal were obtained by fast Fourier transform, and the rotor stability was analyzed. The results show that the steam flow can cause the deformation of seal teeth. The temperature made seal teeth length increase by 1%-1.5%, and the pressure and centrifugal effect had little influence on it. Under the action of thermal and dynamic loads, direct stiffness decreased, direct damping increased first and then decreased, cross-coupling stiffness decreased first and then increased, the maximum variation of dynamic coefficient was twice as before. Rotor stability margin decreased sharply in 35-55 Hz, so the rotor was more sensitive to the steam flow excited vibration. Due to the thermal and dynamic loads, the pressure fluctuations concentrated in low frequency range. The circumferential pressure fluctuations in seal could be increased by 18.5 kPa. The dramatic increase of pressure fluctuations in high pressure zone is the main reason for intense steam flow excited vibration.