Numerical flow field investigation around guide vane of a high head Francis turbine

Abstract

Guide vanes are the most eroded component of the Francis turbine, and flow instabilities around guide vanes influence the flow field at the runner inlet. Guide vane cascade can be considered an alternative method to investigate the flow field, which maintains flow similarity with the prototype turbine. The objective of this paper is to numerically analyze the flow field around the guide vane cascade. A single guide vane cascade numerical model is developed to perform the simulation using commercial software ANSYS 2022. Two turbulence models, shear stress transport k-ω and standard k-ε, perform steady-state simulation at the best efficiency point. The pressure and velocity distribution are obtained at mid-span, and around the pressure and suction sides of the guide vane. Numerical simulation on a scaled prototype full turbine has also been performed to measure the Francis turbine’s torque and efficiency. The modified Bhilangana- III guide vane profile is installed in the B-III hydropower plant in India and taken as a reference Francis turbine. The velocity and pressure distributions obtained around guide vanes of the scaled full turbine are compared with the velocity and pressure distributions of the single guide vane cascade. A difference of 7.25 % in maximum velocity and 9.40 % in maximum pressure at the mid-span of the guide vane is found between the guide vane cascade and scaled full turbine at the best efficiency point. The overall efficiency of the scaled turbine is also measured, and a difference of 0.83 % between the numerical result and scaled hill chart at the best efficiency point was found.