Numerically Simulating the Formation and Motion of Water Films and Erosion-Hazardous Droplets in Flow-Through Parts of Steam Turbines

Abstract

A model for the process of coarse liquid particle formation in the flow-through parts of steam turbines is considered. A numerical approach is proposed to describe the formation and development of a water film on the surface of the interblade channels, and the main factors affecting the distribution of the film parameters along the curvilinear walls of the blades are presented. It is assumed that the only source of the water film is represented by liquid-phase particles deposited on the blade surfaces. The process of film detachment from the exit edge of the blade together with its subsequent destruction and the formation of large erosion-hazardous droplets is considered. The developed model has been integrated into the earlier proposed numerical approach to the description of the motion of liquid-phase particles and their interaction with solid surfaces. At the same time, an amendment has been introduced therein taking into account the presence of a water film when a liquid phase particle collides with a solid wall. The developed numerical method makes it possible to describe all the main gas-dynamic processes occurring in the course of motion for erosion-hazardous droplets in the interblade channels. This method has been tested using experimental studies on streaming wet-steam flow in a flat nozzle grating at different initial humidity of the working medium. Using the laser flux diagnostics system, velocities and sizes inherent in droplets beyond the grating along its spacing have been determined. The developed model provides a good agreement of these parameters with the experimental data in the places of the maximum concentration of coarse droplets. However, there is a significant discrepancy for some areas of the flow in the obtained results concerning the velocity distribution. The effect that the initial steam moisture exert on the characteristics of the water film on the blade surface is considered. It is established that the film thickness significantly affects the interaction between the droplets and the blade surface in the areas wherein the collision energy is small. These areas are characterized by a large angle between the velocity vector of the projectile droplet and that normal to the surface at the collision site.