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.
Effects of reservoir volume on performance of pulse tube cooler.
A pulse tube cooler has the advantages of long-life and low-vibration over conventional cryocoolers such as G-M and Stirling coolers because of the absence of moving parts at low temperature. On the other hand, the combination of a reservoir and orifice is indispensable to optimize the performance of pulse tube coolers. In order to make the pulse tube cooler compact for practical applications, the volume of reservoir should be minimized. This paper analyzes the effects of the reservoir volume on the thermodynamic performance of various components in a simple orifice and a double-inlet pulse tube cooler by combining a linearized model with a thermodynamic analysis. Expressions of entropy production for those components are presented. The results show that the reservoir volume has a significant influence on the entropy production in the various components when the reservoir to pulse tube volume ratio is smaller than about 5. The ratio is important to determine the minimum reservoir volume for a pulse tube cooler. Optimum settings for a double-inlet pulse tube cooler are also discussed.