Analysis of the pump-turbine S characteristics using the detached eddy simulation method

Abstract

Current research on pump-turbine units is focused on the unstable operation at off-design conditions, with the characteristic curves in generating mode being S-shaped. Unlike in the traditional water turbines, pump-turbine operation along the S-shaped curve can lead to difficulties during load rejection with unusual increases in the water pressure, which leads to machine vibrations. This paper describes both model tests and numerical simulations. A reduced scale model of a low specific speed pump-turbine was used for the performance tests, with comparisons to computational fluid dynamics(CFD) results. Predictions using the detached eddy simulation(DES) turbulence model, which is a combined Reynolds averaged Naviers-Stokes(RANS) and large eddy simulation(LES) model, are compared with the two-equation turbulence mode results. The external characteristics as well as the internal flow are for various guide vane openings to understand the unsteady flow along the so called S characteristics of a pump-turbine. Comparison of the experimental data with the CFD results for various conditions and times shows that DES model gives better agreement with experimental data than the two-equation turbulence model. For low flow conditions, the centrifugal forces and the large incident angle create large vortices between the guide vanes and the runner inlet in the runner passage, which is the main factor leading to the S-shaped characteristics. The turbulence model used here gives more accurate simulations of the internal flow characteristics of the pump-turbine and a more detailed force analysis which shows the mechanisms controlling of the S characteristics.

A review of rotating stall in reversible pump turbine

“…Figure 30 shows a typical backflow from the impeller to the guide vanes. Recently, Sun et al 51 and Liu et al 52 also quantitatively studied the distributions of the backflow inside the reversible pump turbine based on the numerical simulations.…”

Aerodynamic Characteristics of Isolated Loaded Tires with Different Tread Patterns: Experiment and Simulation

“…Two turbulence models were employed for calculating the turbulent stresses, two equations of the shear stress transport (SST) k-ω model [33,34], and improved delayed detached eddy simulation (IDDES) model [35]. The SST k-ω model is a two-equation Reynolds average Navier-Stokes (RANS) model that improves the separation prediction in the near-wall region.…”

Numerical Study on the Internal Flow Field of a Reversible Turbine during Continuous Guide Vane Closing

“…The detached eddy simulation (DES) model was proposed by Spalart [27] in 1997 and first used in 1999. In recent years, DES has been successfully used in a large amount of cases including many industry applications [28,29]; it has proven to be more accurate in the presence of prominent separations in the flow domain and better able to capture the flow field details compared to other models [30][31][32]. Furthermore, the DES method has great advantages: it can be applied at high Reynolds numbers, and it is suitable to solve geometry-dependent, unsteady three-dimensional turbulent motions, similar to the large eddy simulation (LES) model.…”