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A Comprehensive Review of Verification and Validation Techniques Applied to Hydraulic Turbines
Chirag Trivedi,Ole Gunnar Dahlhaug 한국유체기계학회 2019 International journal of fluid machinery and syste Vol.12 No.4
The paper critically reviews the verification and validation (VV) techniques applied to investigate hydraulic turbines. Although there are well-established standards such as AIAA G-077-1998 and ERCOFTAC guide for turbulence modelling, majority of studies conducted on the turbines are lacking of systematic VV. Results without proper VV serve no purpose for safe and reliable designs of turbines. Available standards/guide are for general-purpose industrial applications and have limited scope. Customized VV procedure for the turbine applications is essential to create trust on the obtained results. The present review discusses how available standards/guide can be used to determine uncertainty/error and to demonstrate the credibility of results. The review includes several aspects of VV such as effect of discretization schemes, iterative error, convergence criteria, time-step sizing and impact of passage modeling approaches on the results. Further, how numerical results mislead the user and its implications are addressed. In the last, open questions on turbine modelling and recommendations on prospective numerical studies are discussed.
Numerical and experimental study of the leakage flow in guide vanes with different hydrofoils
Sailesh Chitrakar,Biraj Singh Thapa,Ole Gunnar Dahlhaug,Hari Prasad Neopane 한국CDE학회 2017 Journal of computational design and engineering Vol.4 No.3
Clearance gaps between guide vanes and cover plates of Francis turbines tend to increase in size due to simultaneous effect of secondary flow and erosion in sediment affected hydropower plants. The pressure difference between the two sides of the guide vane induces leakage flow through the gap. This flow enters into the suction side with high acceleration, disturbing the primary flow and causing more erosion and losses in downstream turbine components. A cascade rig containing a single guide vane passage has been built to study the effect of the clearance gap using pressure sensors and PIV (Particle Image Velocimetry) technique. This study focuses on developing a numerical model of the test rig, validating the results with experiments and investigating the behavior of leakage flow numerically. It was observed from both CFD and experiment that the leakage flow forms a passage vortex, which shifts away from the wall while travelling downstream. The streamlines contributing to the formation of this vortex have been discussed. Furthermore, the reference guide vane with symmetrical hydrofoil has been compared with four cambered profiles, in terms of the guide vane loading and the consequent effect on the leakage flow. A dimensionless term called Leakage Flow Factor (Lff) has been introduced to compare the performances of hydrofoils. It is shown that the leakage flow and its effect on increasing losses and erosion can be minimized by changing the pressure distribution over the guide vane.
The Rotor-Stator Interaction Onboard A Low Specific Speed Francis Turbine.
Einar Agnalt,Bjørn Winther Solemslie,Pal-Tore Selbo Storli,Ole Gunnar Dahlhaug 한국유체기계학회 2020 International journal of fluid machinery and syste Vol.13 No.2
Over the last years, several breakdowns in hydropower plants with low specific speed Francis runners have been reported. One of the main excitation forces in such runners is the pressure fluctuations originating from the rotor stator interaction. In this paper, the rotor-stator interaction has been analyzed utilizing pressure sensors onboard the runner. The pressure sensors were flush mounted in the hub of the runner and the signals were transmitted through a slip-ring system. The measurements have been analyzed relative to the runner angular position by utilizing an angular position sensor mounted to the shaft end. Measurements with different guide vane angle have been compared in order to study the potential flow interaction and the viscous wake effects for the pressure inside the runner. The results from the onboard pressure measurements found that the phase of the guide vane passing pressure seen by the onboard pressure sensors was independent of the guide vane opening. Hence, the potential flow interaction was found to be the dominant effect and no evidence from the viscous wake effect was found on the onboard pressure.