REVIEW OF THE PROBLEM OF FATIGUE STRENGTH OF RADIAL-AXIAL HYDRAULIC TURBINE WHEELS

Assessment of the strength, reliability and service life of hydraulic turbines is a topical task at all stages of the equipment life cycle, covering a whole range of theoretical, computational and experimental works. One of the important stages of this complex is the calculation justification of the service life characteristics of hydraulic turbines, which are determined mainly by the stress-strain state of the service life-determining elements, primarily the runner. The paper presents an analysis of models and methods for studying the static and dynamic stress-strain state of runners of hydraulic turbines. The level of static and dynamic stresses significantly depends on the operating mode of hydraulic turbines, their design and individual qualities, which are characterized by the conditions of installation and operation. During long-term operation, the main reason for the exhaustion of the resource of impellers is the accumulation of fatigue damage, which leads to a violation of the integrity of the structure. To assess the fatigue strength of hydraulic turbine structures, it is necessary to establish the history of loads and develop thorough calculation methods based on fracture mechanics. The analysis carried out showed that at present the issue of studying the fatigue strength of impellers of radial-axial hydroturbines does not have a complete solution. The ideal validated numerical approach allows for further study of harmful flow phenomena using external sensors on the machine block. Subsequent factory measurements on selected units of hydraulic turbines are extremely important. A combined approach to calculations and measurements, when all flow phenomena are simultaneously investigated, will lead to achieving the required fatigue strength of hydroturbine impellers. The article is part of a series of several publications on the topic of fatigue strength analysis of Francis turbine prototypes in the procedure of multi-level service life assessment. The carried out analysis of problematic aspects made it possible to note that new approaches, models and methods and means for studying the fatigue strength of runners are needed, which create a basis for substantiating progressive technical solutions for radial- axial hydraulic turbines.