EXPERIMENTAL AND CALCULATION STUDY OF PRESSURE PULSATIONS IN THE RADIALAXIAL HYDROTURBINE

Abstract

The force interaction of the vortex swirls in the draft tube of the hydraulic turbine RO with the elements of the flow path can lead to serious accidents. Reducing low-frequency pressure pulsations is an urgent task, as it helps to increase the reliability and increase the power of hydraulic units. For this, special devices are sometimes used. The aim this of the work was to compare modern methods for calculating low-frequency bundle pressure pulsations in a draft tube with experiment. Experimental studies of pressure pulsations in the flow part and the impeller blade of the RO115 hydraulic turbine were carried out in a wide range of operating modes. Numerous experiments were carried out to determine the bundle pressure fluctuations using a spatial mathematical model according to the method of NTU ''KhPI''. In addition, calculations of pressure fluctuations were performed based on a modern hydrodynamic software package that solves problems of continuum mechanics and uses the Reynolds equation. The process of solving problems in this case is carried out by means of the CFD application package, which includes the following steps: creating a three-dimensional model of the object under consideration using the CAD system; construction of the computational grid; choice of mathematical model of turbulence; problems of limiting conditions. A comparison of the experimental and calculated results indicates their good agreement. Prediction of pressure fluctuations using the above methods when designing hydraulic turbines makes it possible in the future to choose the best flow path with lower pressure fluctuations (with lower losses) and with higher energy-cavitation performance. In the first case, the task requires insignificant resources of computer time, and the error in calculating the amplitudes of pressure fluctuations is up to 15 % compared with the experimental data, in the second case it is 10 % with a much longer calculation time. In the future, the results of calculations of bundled pressure pulsations are used in strength calculations of elements of the flow path of a hydraulic turbine with large margins in terms of strength factors, so it is possible to use mathematical models of varying complexity in predictive calculations of bundled pressure fluctuations in a draft tube.