Avaliação de desempenho e erosão por cavitação e sedimentos em turbinas axiais através de simulação numérica

Abstract

This work presents an evaluation of the performance and the erosion effects caused by cavitation and sediments in an ultra-low head axial hydraulic turbine, using numerical simulation techniques. The study is based on design data and experimental results provided by Souza (1988), which served as a reference for building the computational model and validating the analyses. Initially, the fluid domain of the turbine was developed based on the geometry of the rotor and guide vane profiles, obtained from planar coordinates and later converted into cylindrical coordinates. Mesh generation was carried out using ANSYS TurboGrid software, following established quality criteria and subjected to a mesh independence study to ensure accurate representation of the computational model. Boundary conditions were defined according to the closed-loop flow regime, with flow and pressure controlled by a butterfly valve and sluice gate, along with the implementation of multiphase models to represent cavitation and particle-fluid interaction. The cavitation phenomenon was modeled using the Rayleigh-Plesset model, while the erosion caused by sand particles of varying diameters was assessed through the Finnie model. The results showed good agreement between the numerically obtained characteristic curves and the experimental data, validating the proposed flow field model. It was also observed that cavitation is concentrated on the suction side of the rotor blades, whereas particle erosion primarily affects the pressure side and the casing region. It is concluded that ultra-low head turbines should be designed to operate outside cavitating zones and, in environments with high sediment concentration, the use of abrasion-resistant materials and the adjustment of operating conditions are recommended to mitigate degradation.