Methodology to Predict Effects of Leakage Flow from Guide Vanes of Francis Turbine

Abstract

Leakage flow from clearance gap affects the performance of Francis turbines. This study presents the method to predict the effects of leakage flow from clearance gap of GVs. When sediments flow along with water through guide vanes it erodes the guide vane's surface. Clearance gap of the guide vanes gradually increases due to continuous effects of abrasive wear. This phenomena of abrasion deteriorates the overall performance of the turbine. In this study, the effects of increased clearance gap of GVs of Francis turbine are studied numerically. Numerical models including the clearance gap-size of 0 mm, 2 mm and 4 mm are made to compare the effects. It uses alternative leakage flow approach, whereby current model consisting of 24 GVs contains 12 clearance gaps alternatively. This approach makes it possible to differentiate the amplitude of pressure pulsations contributed either by wakes or vortices due to leakage flow from guide vanes. Comparing the 3 different cases, it was found that increased clearance gap of the guide vanes increases the pressure pulsation at the runner inlet, reducing overall efficiency of the turbine.