The aim of this paper is to introduce a novel approach for analysing the droplet formation in a transonic flow. The method suggested in this work is based on the combination of the measured data from the wind tunnel by an optical measurement and image processing. A new wind tunnel was developed for the study of the liquid film atomization at high speed flows similar to ones that can be found in steam turbines. The coarse droplets in steam turbines are formed from the liquid films on the blades and inner casings. The coarse droplets formed on the stator blades don´t follow the bulk flow and collide with the following moving blades. These collisions cause erosion and corrosion processes, which have an unfavourable effect on the reliability and the efficiency of the low pressure stages of steam turbines. The tunnel is equipped with a standard instrumentation for the measurement of the flow properties and for the analysis of the size distribution of the droplets. Two measurement methods were used for the measurement of the size of the droplets, photogrammetry and light scattering. In this paper, the image processing of the captured images is discussed. The images were taken by a camera with a telecentric lens. The paper contains an assessment of three image processing methods used for the measurement of the droplet distribution by the light extinction. Moreover, the formation of the droplets is captured on the trailing edge of the profile in the flow. The results bring a new view on the formation of droplets at high speeds.

The paper introduces the experimental results of the droplets formation for three different aqueous solutions. The new wind tunnel was built to study water droplets atomization from liquid films at high speed flow similar to that found in steam turbines. Liquid atomization is a widely studied problem for sprays and generally in the field of aerosol research. A similar phenomenon occurs in steam turbines but mainly with undesirable effects, the formed droplets from the film (coarse droplets) have a negative effect on the reliability and efficiency of the turbines due to the erosion and corrosion by the droplets impact on the leading edges of the blades. The new wind tunnel is equipped with classical pressure and temperature measurement systems for the determination of the initial condition in the settling chamber and measurement of the static pressure along the nozzle with a known profile. The photogrammetric method and light scattering are used to measure the diameter distribution of the droplets. The liquid film is made with an aqueous solution supplied on the symmetrical aerofoil NACA 0008. Different aqueous solutions were studied for different liquid surface tension effects.

No abstract

The paper introduces the first results from a new steam/air wind tunnel built in order to study the coarse water droplets in steam turbines and their formation. The wind tunnel was designed with the aim to have a testing facility with similar flow conditions for the study of liquid films as found in steam turbines. The tunnel is equipped with common devices for the measurement of the flow and for the analysis of the diameter distribution of the droplets. Two measurements methods were used for the measurement of the droplets size, photogrammetry and light scattering. The liquid film is artificially produced on an airfoil placed in the nozzle and liquid is pumped by a dosing pump on the surface of the airfoil. Coarse droplets formed from the liquid films have a negative effect on the reliability and efficiency of the turbines due to the erosion and corrosion by the droplets impact on the leading edges of the blades.

The aim of the paper is to introduce and compare various methods which can be used for an image processing. Studied methods include the image pre-processing and the image segmentation based on the Gaussian mixture model and the active contour. The images are acquired within the measurement of the liquid film disruption on the aerofoil‘s trailing placed edge in the wind tunnel. As the result is suggested sequence of the particular image processing techniques for an optimal result. This work is the part of the wider project devoted to the coarse water droplets which have a negative effect on the steam turbines efficiency and reliability.