Geometry, Mesh and Numerical Scheme Influencing the Simulation of a Pelton Jet with the OpenFOAM Toolbox

Abstract

Hydropower is a key source of electricity production for allowing the integration of intermittent renewable energy resources. Among the various hydraulic power plants around the world, the ones equipped with Pelton turbines already provide large flexibility that is still enhanced with the development, for instance, of the hydraulic short circuit operating mode. However, the knowledge of the flow inside Pelton turbines is still a challenging task, both numerically and experimentally, despite progress in the last two decades. One key feature of the Pelton efficiency is the jet quality, i.e., the jet velocity needs to be uniform, not perturbed by secondary flows and compact. The compactness of the jet is mainly dependent o nthe location of the jet detachment at the nozzle outlet, which is challenging for computational fluid dynamics simulations mainly due to numerical diffusion. Even if this point has already been mentioned in previous papers, the present paper focuses on all the parameters that can influence the jet detachment: the nozzle geometry, the mesh and the numerical scheme used to discretize the convective fluxes. The simulations of an existing Pelton injector are performed using the OpenFOAM toolbox. It is noticed that, in addition to the nozzle geometry and the mesh resolution at the nozzle outlet, the choice of the numerical schemes influences the jet detachment and, consequently, the jet diameter and discharge. The use of an anti-diffusive scheme such as the “SUPERBEE” limiter improves the prediction of the jet in accordance with the on-site measurements.