Abstract
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.
Highlights
The liquid film disruption is an important topic in the field of aerosol research [1], but a general solution for different engineering applications is still missing
Size distribution and aerodynamics Optical measurement device Spraytec was used for the measurements of the size distribution function of the swept droplets behind the aerofoil
Due to the existence of the bi-modal size distribution, the data of the size distribution function were divided into two groups and for both groups, the Sauter mean diameter was computed separately
Summary
The liquid film disruption is an important topic in the field of aerosol research [1], but a general solution for different engineering applications is still missing. Water film disruption is known to occur in steam turbines. The coarse droplets formed from the films on blades and casings are related with undesirable effects on the reliability and efficiency of steam turbines [2, 3]. As an example of other practical applications where liquid films are involved, the effect of rain on wind turbines and airplane wings could be mentioned. Due to the wide range of engineering applications of the liquid film break-up, this paper is focused on the conditions in steam turbines.
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