Reversible Francis pump turbines. Improvement of part load performance by changes on the design of impeller blades

摘要

The effects of changes on the impeller blades hydraulic design, increasing the number and the curvature of impeller blades, are analyzed at part load performance. The objective of this research is to find the convenient changes on impeller blades design that reduce the pressure fluctuations at part load. Three pump-turbines impellers with different impeller blade design have been tested in the same casing, from the best efficiency point to decreasing flows. Numerical and experimental results have been obtained in pumping and generating modes. A basic presentation of the physical mechanisms that produce hydraulic instabilities, and understanding of the effects of flow separation on characteristics and pressure fluctuations is given as a means of qualitatively analyzing part load operation. The experimental methods provide information about the characteristics, overall efficiency, energy, velocity components and pressure pulsations. The results obtained include efficiency, characteristics, impeller outlet energy and velocity components and unsteady pressure. The numerical methods apply the finite difference method to the quasi-three-dimensional approximation to solve the inviscid part of the flow. Losses correlation has made possible to run this program at operating points different from design operation. The results are presented in form of meridional relative streamlines, blade loading - velocity, blade loading - pressure, incidence and deviation angles. From the analysis of the results can be concluded that the geometrical and hydraulic parameters are strongly related at part load performance. The increase of number of blades and impeller blade curvature decreases the level of blade loading and produces a more uniform blade loading distribution along the blade. The unsteady forces can be reduced by convenient changes on impeller blades design. 44 refs., 96 figs., 14 tabs.