Numerical study on the effect of operating conditions on cavitation in Kaplan turbine
Kaplan turbines, like other hydraulic turbines are designed explicitly for the rated operational conditions specific to every hydropower plant. Variations in electricity demand and inlet flow conditions like mass flow rate and net head, force the turbines to run at off-design operational conditions, which increases cyclic loading in stationary and rotating components and leads to cavitation. Due to the high specific speed of Kaplan turbine, it is necessary to determine the cavitation characteristics. The present analysis aims to examine the influence of the cavitation phenomenon on the various operating conditions using the ANSYS CFX. Detailed flow analysis is conducted for part-load, full load, best efficiency point and overload operating conditions. The stages of cavitation development in the runner are extensively studied for various operating regimes. The key points of the present work are the critical analysis of various flow parameters for cavitating and non-cavitating analysis. The value of critical cavitation factor is found to be 0.34, 0.39, 0.57 and 0.61 at 35º, 40º, 50º and 60º guide vane opening, respectively. The results obtained by this investigation have been validated with the results of experimental model testing of turbine. The present investigation is very realistic and related to the actual site conditions.