Numerical Prediction Of Torque On Guide Vanes In A Reversible Pump-Turbine Turbine and pump mode operation
The paper presents the numerical flow analysis of the torque on guide vanes pivots in reversible pump-turbine (PT) in turbine and pump mode operation. Flow conditions in a typical PT often point out the importance of the unsteadiness of the flow, first of all because of its instability caused by the viscous effects – the boundary layer separation, vortex spreading and the influence between rotating and non-rotating parts. The detailed analysis of the time dependent distribution of torque on guide vanes is presented. The numerical analysis was performed for complete pump-turbine with various turbulence models. The numerical results were compared with the experimental results. Keywords—water turbine, reversible pumpturbine, CFD, guide vanes, dynamic chyracteristics
Determination of hydraulic losses in the flow passage between the guide vanes and runner of the Kaplan turbine
ABSTRACT Hydraulic losses in the region between the guide vanes and runner of a Kaplan turbine are commonly either neglected or considered a part of the total guide vanes losses. This paper focuses on the determination of these losses for a relevant range of operating modes of the Kaplan turbine model. The research was performed by numerical simulations using two turbulence models, wherein some of the results were validated by the available experimental data. The impact of swirl flow parameters, defined for referent inlet of the researched vaneless passage, on the hydraulic losses was considered. Based on the numerical and experimental results, a novel formula for determination of these losses is proposed. The contribution of the studied losses to the total turbine losses is also identified.
A Scale-Adaptive Simulation Model using Two-Equation Models
The Scale-Adaptive Simulation (SAS) concept is based on the introduction of the von Karman length-scale into the turbulence scale equation. The information provided by the von Karman length-scale allows SAS models to dynamically adjust to resolved structures in a URANS simulation, which results in a LES-like behavior in unsteady regions of the flowfield. At the same time, the model provides standard RANS capabilities in stable flow regions. The introduction of the von Karman length-scale is based on the reformulation of Rottas’s equation for the integral length-scale. In the current paper, the term containing the von Karman length-scale is transformed to the SST turbulence model. It allows the SST model to be operated in a SAS mode.