Prediction of the Occurrence of One-Dimensional Pressure Surge in an Elbow Draft Tube

Abstract

Based on the explanation of one dimensional draft tube surge induced by the cavitated vortex rope, i.e., it occurs when the rotating frequency of the vortex rope at the elbow portion coincides with the resonance frequency of the vibrating system of the draft tube with a cavitation region, we developed a theoretical method to predict the occurrence of severe pressure fluctuation. In the present study, a partially rolled-up vortex model was proposed to calculate the rotating frequency of the vortex rope, and a method was presented to estimate the cavitation volume in the draft tube, which is the main parameter to determine the resonance frequency of the vibrating system. The calculated and experimental results were compared, and reasonable agreement was obtained.