Wet-Steam Flow Simulation With Coarse Water Droplets Through a Turbine Cascade Based on Eulerian-Eulerian Method

Accurate prediction of wetness losses caused by water droplets in steam turbines is essential for enhancing the stability and efficiency of power generation systems. This study numerically simulated wet steam flows in a turbine cascade using the Eulerian-Eulerian method, treating water droplets as a continuous phase. The conservation equations for mass, momentum, energy, and number density of water droplets were coupled with the compressible Navier-Stokes equations. The drag force arising from the slip velocity between the steam flow and water droplets was calculated under the assumption of spherical water droplets. Droplet growth via condensation was incorporated into the mass generation rate in the numerical simulation. The inlet droplet diameter was set at 2, 5, or 10 μm. Furthermore, the droplet size distribution at the inlet was modeled using five droplet sizes based on the Nukiyama-Tanazawa distribution function. For 2 μm droplets, some passed through the turbine cascade without colliding. In contrast, for 5 and 10 μm droplets, most collided with the blade surface due to differences in the drag force resulting from slip velocity. These results indicate that droplet motion in the turbine cascade is influenced by droplet diameter, with droplet behavior in the 1–10 μm range strongly tied to slip velocity. In the 2 μm case, slip velocity led to energy losses downstream in regions with a high number density of water droplets. Additionally, droplets passing through the cascade exacerbated energy losses due to condensation. Capturing loss was investigated by integrating the surface collision rate and droplet velocity. The capturing loss for 10 μm droplets was lower than for 5 μm droplets because of the acceleration between blades. Losses were classified into profile, acceleration, and condensation losses for Sauter diameter conditions of 7.5 μm. The present method predicts the wetness loss considering the slip velocity for each droplet size.