Experimental and numerical validation of a Francis turbine draft tube designed for mitigation of pressure fluctuations

Abstract This paper presents an experimental and numerical investigation of the internal flow in a Francis turbine draft tube previously designed for minimizing pressure fluctuations energy losses off-design conditions. The design geometry is based on original approach combining Design Experiments steady/unsteady Computational Fluid Dynamics (CFD) simulations flow. proposed method provides new insight influence dynamic behaviour one hand enables determination promoting stability hydraulic performance another hand. CFD final showed promising results terms compared with initial by conventional CFD-aided methods. A reduced-scale model prototype machine featuring finally installed tested laboratory. Tests include measurements over complete operating range. analysis shows that remains globally stable part-load range amplitude lower than 1% net head. It also shown dominant component at runner outlet cone synchronous nature. physical mechanisms excitation are highlighted unsteady simulation results.