Atomized Droplet Size Distribution in Wake of Fixed Blade.

Abstract

The presence of water droplets in the flow of a steam turbine leads to erosion of moving blades because of the large blade tip speed and higher local wetness. Since erosion resistance is strongly influenced by the impact droplet velocity and size as well as the hardness of the blade material, estimating the distributions of droplet size and frequency is important for establishing erosion criteria. In this paper we describe an estimation method for droplet size of dispersed water flow in the wake of a fixed blade, which can be extended to a moving blade. The LDV system was applied to measure velocity and size of droplets in the wake near the trailing edge of a fixed blade, under conditions simulating those found in the last stage of a low-pressure steam turbine. Test results show that droplet sizes in the wake of a fixed blade can be approximately evaluated by a normal distribution function depending on the mean droplet diameter. It is concluded that the size and frequency distributions of the droplets which impact on a moving blade can be calculated using these characteristics.