Influence of Axial Clearance on Flow Field in the Rotor Cascades and Law of Droplet Deposition in a Humidity-Removing Stage

It selects three different axial clearances in a special humidity-removing stage of steam turbine. It is assumed that the position dropped off the coarse droplets is the trailing edge of the stationary blade, based on the formation of the coarse droplets. Ten sites are set on the trailing edge averagely along the blade height. Three representative water droplets ejecting from these sites are investigated. The flow fields of the stage are simulated by solving the steady three dimensional Reynolds averaged Navier-Stokes equations on the basis of the real steam thermo-physical properties, and the Lagrangian tracking is implemented for water drops transport. The results indicate that the loads of the blade root are not only greatly reduced, but also the incidence angles of the moving blade will be changed as it increases the axial clearance. As a result, it is propitious to decrease the boundary layer loss of blade suction section, while the secondary loss of the root endwall will be enhanced. By comparative analysis for the wall deposition laws of three different diameter droplets, it reaches the conclusion that the same size of water droplet basically has the same deposition law at three different axial spacings. Moreover, the probability of the large water droplets injection to the blade tip between the stator and the rotor rises with increasing the axial clearance, then more of the water is emitted off the passages of the stage through the drain rings set on the blade tip. So the erosion on the suction surface of the moving blades is reduced and the operational safety for steam turbine is improved.