Experimental Studies of Diffuser Fins Effect in Pump-Turbine Draft Tube on Pressure Pulsations in Turbine Mode

One of the methods of reducing the level of pressure pulsations in the flow part of a Francis pump-turbine for a heads up to 200 m by installing straightening fins in the suction pipe diffuser is experimentally investigated. The model of the Dniester PSP hydraulic machine with two types of runners was chosen as the object of study: RK5217, which is installed on units 1–4 of the plant, and its modification RK5217M2. The tests were conducted on the hydrodynamic test stand for a model with runner diameter of D₁ = 350 mm. The stand has the status of a national heritage, meets the requirements of IEC 60193 for model studies of hydraulic machines and has an efficiency measurement error of ±0.25%. The runner blades and fins were made using 3D printing technology from PLA plastic, which significantly reduced the cost and time of the work. The study was conducted both without fins and with two versions of fins of different lengths installed in the diffuser. The pressure sensor is located in the diffuser behind the fins at a distance of 1.5D₁ from the outlet of the runner. A comparison of the pulsation characteristics of the models with fins 170 and 300 mm long and without them at reduced rotational speeds corresponding to the minimum, nominal, and maximum heads at the Dniester PSP is presented. The pulsation characteristics of models with different runners are compared. It is shown that the length of the fins practically does not affect the pulsation characteristics in the draft tube diffuser.