BEFORE FEEDING THE INTEGRATED PERFORMANCE OF WORKING WHEELS OF RADIAL- AXLE HYDROTURBINS

The unique impellers of high-pressure hydroturbines are large in size and mass and are manufactured as welded structures, in which the top rim, bottom rim and each blade are cast separately and then welded, or sometimes made as a single piece. Due to the operating conditions of hydroturbines, individual parts of the impeller (blades, lower rim) are made of cavitation- and corrosion-resistant chromium steels. The welded design allows for the production of combined impellers: the parts prone to cavitation are made of stainless chromium steels, the rest are made of cheap low-alloyed ones. Cracks that usually start in places of stress concentration and after brewing appear again after some time. In impellers cast as a whole, fatigue failures also occur during the operation of hydroturbines, they are caused by vibration of the unit as a result of pulsation of the pressure of the water flow, vortex formation, cavitation along with hydroabrasive wear. Fatigue cracks and fractures most often occur at the inlet and outlet edges of the blade, where dynamic loads are superimposed on the constant, maximum static load from the water pressure. The methods of combating cracking, research methods and modeling of the operational load of the blades are considered. Calculations of the fatigue strength of the working wheels made it possible to draw conclusions about their stressed state. Real-life and model experiments were conducted to determine the levels of pressure pulsation in the impellers of high-pressure radial-axial hydroturbines at a head of 300 meters. The results of these studies can be considered as initial data for their further use in calculations of the fatigue strength of the impellers of high-pressure radial-axial hydroturbines in modern 3D models.