Hydraulic Improvement to Eliminate S Shaped Curve in Pump Turbine

Abstract

For pump turbines, an Sshaped curve can lead to failures in synchronization. To improve the hydraulic design, the component that is responsible for the formation of the Sshaped curve was identified by a hydraulic loss analysis using previous computational fluid dynamics (CFD) results, which indicates that the formation of the Sshaped curve can be ascribed to the runner. To improve the hydraulic design of the runner, a simple numerical approach for direct problem analysis was proposed, based on the bladeloading distributions of runners with and without an Sshaped curve, and directly analyzed. It was implied from the differences in the bladeloading distributions that, when the meridional passage was broadened, the formation of the Sshaped curve was suppressed. To validate this, two runners with different meridional sections were designed by means of the inverse design method. Through model tests, it was verified that the Sshaped curve was eliminated completely and the performance curve of the modified hydraulic model satisfied the requirements for safe operation in a pumped storage plant.