Unsteady Force on Multi-Stage and Multi-Passage Turbine Long Blade Rows Induced by Wet-Steam Flows

At the 2015 ASME Turbo Expo in Montreal, we presented a paper on unsteady three-dimensional wet-steam flow simulations for the last three stages of a low-pressure real steam turbine. We then focused on the investigation of unsteady wetness in the three-stage blade passages, which was conducted by assuming the same number of blades in the previous study and the real blade number. The obtained results showed that wetness is definitively influenced by the blade number difference between the stator and the rotor. This paper presents a numerical investigation of unsteady pressure forces on the multi-stage blade rows caused by stator-rotor interactions, which include unsteady wakes, vortices, shocks, and wetness. In particular, we investigate the effect of blade number variation on the pressure forces. Our results indicate that unsteady pressure forces are significantly influenced by shocks from the upstream stator trailing edges transferred to the adjacent rotor blade noses. We finally found that the unsteady pressure forces on the rotor blades are strongly influenced by shocks from upstream stator trailing edges near the hub region and the forces result in a time-dependent torque difference between neighboring two rotor blades.