Numerical Modeling of Water Droplets in Compressible Two-Phase Flows Based on Eulerian-Eulerian Method

Abstract The slip velocity between water droplets and gas phase causes losses in steam turbines. The accurate prediction of the motion of coarse water droplets in wet-steam flows is crucial for the prediction of efficiency and erosion. In this study, the Eulerian-Eulerian method, which assumes water droplets as a continuous phase, was developed to simulate the motion of coarse water droplets in compressible two-phase flows. The conservation equations consisting of mass, momentum, energy, and number density for coarse water droplets, were coupled with compressible Navier-Stokes equations. Additionally, drag forces owing to the slip velocity between the water droplets and the gas phase were included in the model. Dry-air and moist-air flows through a subsonic turbine cascade were simulated. The inlet droplet sizes were set to 0.5, 5.0, and 10.0 μm in each computational case. Under dry conditions, the numerical results produced the increase in the loss in the wake region. Under wet condition, 0.5 μm droplets went through the cascade without colliding with the blade surface because of the high drag coefficient for fine droplets. 5.0 and 10.0 μm droplets partially collided with the blade surface owing to the slip velocity between the droplets and the gas phase. While the nondimensional losses in case of the 0.5 μm droplets were higher than experimental results at each pitch position, those of the 10.0 μm droplets had a maximum peak in the wake region. The present method enables to produced losses by the slip velocity in each droplet size. The nondimensional losses of the experiments were reproduced by considering the particle size distribution and volume rate of droplets.