Developments for Modeling of Droplets Deposition and Liquid Film Flow in a Throughflow Code for Steam Turbines

Modeling wetness phenomena in steam turbines can help to assess the weight of the different losses due to the liquid phase, and so provide a tool to evaluate possible design features and optimal operating conditions. Since this analysis involves a whole section flow path, throughflow approach is more suitable than 3D CFD. The paper presents a way to model deposition of fog droplets and motion of liquid film on blades in a wet steam turbine in a throughflow code. For deposition, the contribution of turbophoresis is taken into account by using the deposition rate model established by Zaichik et al. and the contribution of inertia is considered for deposition on the leading edges of blades. The liquid film model considers liquid film as a surface entity, the mass and momentum conservation equations being integrated on the film thickness to calculate the averaged film thickness and velocity. The liquid film is submitted to aerodynamic drag, blade friction and inertial effects. This model is validated with an experiment conducted at the University of Michigan. A parametric study on droplet size, thermodynamic conditions, friction velocity and on correction for rarefied gas effect has been performed on a single stage transonic turbine.