Numerical study on the effect of guide vane opening and draft tube outlet pressure on cavitation in Kaplan turbine

Abstract

variations in electricity demand and site conditions like mass flow rate and net head, force the turbines to operate under off-design conditions. This increases cyclic loading in stationary and rotating components and severe cavitation in low head turbines like Kaplan turbine. The present analysis aims to examine the influence of various operating conditions on hydraulic efficiency and cavitation characteristics using ANSYS CFX. The stages of cavitation development in the runner are extensively studied for different operating conditions. The key point of present work is the critical analysis of various flow parameters for cavitating and non-cavitating conditions. The value of critical cavitation factor is found to increase from 0.34 to 0.61 with an increase in guide vane opening from 35º to 60º. The blade loading and flow parameters are found to be affected due to changes in guide vane opening and cavitation. The computed results are validated with the experimental model testing results and found to bear close comparison.