A Study of Transient Flow Modes in a Hydraulic Turbine Draft Tube Model

Abstract

Results are presented of experiments carried out using an air model of a hydraulic turbine draft tube. These included velocity measurements in the conical part of the tube using a laser-Doppler anemometer and measurement of pressure pulsations using acoustic sensors (microphones). It is shown that a system of two runner vane cascades can be used to simulate a velocity distribution that resembles the distributions downstream of a runner under full-scale conditions. Experiments show that modes involving the formation of a vortex rope occur in the region of significant hydroelectric generating unit underload. Analysis of spectra, the cross-correlation function, and mean velocity distributions confirmed the vortex nature of the generation of powerful pressure pulsations in the draft tube cone.