Numerical Analyses of Cavitating Flow in a Pelton Turbine

Abstract

Erosion and wear of hydraulic surfaces are frequent problems in hydraulic turbines, which lead to a decrease of the performance in time and/or in extreme cases to the rotor mechanical failure. These circumstances have negative repercussions on the annual produced power due to the decay of the efficiency, the delivered power, and to the off line periods as result of ordinary and extraordinary hydraulic profiles maintenances. Consistently, the study of this wearing process is an important step to improve the impeller design, and to avoid or minimize the rise of extraordinary maintenance. While mechanical damages are well documented and studied, little information can be found on cavitation in Pelton turbines. In this paper, a CFD model was applied to study the cavitation mechanics on a Pelton turbine. A Pelton runner affected by pitting cavitation was taken as a test case. The bucket geometry was modeled and analyzed using unsteady Reynolds averaged Navier-Stokes (RANS) multiphase analyses. Numerical results allowed us to highlight the different vapor productions during the cut-in water jet processes by the bucket. Furthermore, a simple procedure to identify the locations of higher damage risk was presented and verified in the test case runner.