Secondary droplet erosion in the penultimate stage of a nuclear power large steam turbine was investigated by CFD on the basis of the finite volume method. The discrete phase transport model of the water droplets was solved using the Lagrangian formulations
and the Eulerian conservation equations were applied to solve the steam flow in blade cascades. The mathematical model of steam flow and droplets movement in the cascade passage was established. The influence of axial clearance on the movement characteristic and deposition of secondary droplets was examined under the steady condition. The results show that the movement of all the water drops from the trailing edges of the stationary blade displays the tendency to slope up to the tip and then the deposition rates of water drops on all the walls in the blade passage can be obtained. The impact velocity of secondary drops on the moving blades decreases and the deposition rate of large droplets dropping onto the top of axial clearance increases if the axial clearance is greater. In addition
the suitable positions of the moisture-removal grooves should be distributed from the leading edge to 50% axial chord of the rotating blades according to the concentrated deposition areas of large droplets.
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