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- Conventional Hydro
Simulation, Analysis and Mitigation of Vortex Rope Formation in the Draft Tube of Hydraulic Turbines
Lead Companies
The Pennsylvania State University
Lead Researcher (s)
- Hosein Foroutan
Flow in the draft tube of a hydraulic turbine operating under off-design conditions is very complex. The instability of the swirling flow may lead to the formation of a helical precessing vortex called the “vortex rope”. The vortex rope causes efficiency reduction, severe pressure fluctuation, and even structural vibration. The primary objectives of the present study are to model and analyze the vortex rope formation using high fidelity numerical simulations. In particular, this work aims to understand the fundamental physical processes governing the formation of the vortex rope, and to investigate the capability of turbulence models to simulate this complex flow. Furthermore, mitigation of the vortex rope formation is addressed. Specifically, a vortex rope control technique, which includes injection of water from the runner crown tip to the inlet of the draft tube, is numerically studied. A systematic approach is considered in this study starting from the simplest and advancing towards the most complicated test case. First, steady simulations are carried out for axisymmetric and three-dimensional grids in a simplified axisymmetric geometry. It is shown that steady simulations with Reynolds-averaged Navier-Stokes (RANS) models cannot resolve the vortex rope, and give identical symmetric results for both the axisymmetric and three-dimensional flow geometries. These RANS simulations underpredict the axial velocity by at least 14%, and turbulent kinetic energy (TKE) by at least 40%, near the center of the draft tube even quite close to the design condition. Moving farther from the design point, models fail in giving the correct levels of the axial velocity in the draft tube. This is attributed to the underprediction of TKE production and diffusion near the center of the draft tube where the vortex rope forms. Hence, a new RANS model taking into account the extra production and diffusion of TKE due to vortex rope formation is developed, which can successfully predict the mean flow velocity with as much as 37% improvements in comparison with the realizable k-ε model. Then, unsteady simulations are performed, where it is concluded that Unsteady RANS (URANS) models cannot capture the self-induced unsteadiness of the vortex rope, but instead give steady solutions. The hybrid URANS/large eddy simulation (LES) models are proposed to be used in unsteady simulations of the vortex rope. Specifically, a new hybrid URANS/LES model in the framework of partially-averaged Navier-Stokes (PANS) modeling is developed. This new model is one of the main contributions of the present study. The newly developed PANS model is used in unsteady numerical simulations of two turbulent swirling flows containing vortex rope formation and breakdown, namely swirling flow through an abrupt expansion and the flow in the FLINDT draft tube, a model-scale draft tube of a Francis turbine. The present PANS model accurately predicts time-averaged and root-mean-square (rms) velocities in the case of the abrupt expansion, while it is shown to be superior to the delayed detached eddy simulation (DDES) and shear stress transport (SST) k-ω models. Predictions of the reattachment length using the present model shows 14% and 23% improvements compared to the DDES and the SST k-ω models, respectively. For the case of the FLINDT draft tube, four test cases covering a wide range of operating conditions from 70% to 110% of the flow rate at the best efficiency point (BEP) are considered, and numerical results of PANS simulations are compared with those from RANS/URANS simulations and experimental data. It is shown that RANS and PANS both can predict the flow behavior close to the BEP operating condition. However, RANS results deviate considerably from the experimental data as the operating condition moves away from the BEP. The pressure recovery factor predicted by the RANS model shows more than 13% and 58% overprediction when the flow rate decreases to 91% and 70% of the flow rate at BEP respectively. Predictions can be improved dramatically using the present unsteady PANS simulations. Specifically, the pressure recovery factor is predicted by less than 4% and 6% deviation for these two operating conditions. Furthermore, transient features of the flow that cannot be resolved using RANS/URANS simulations, e.g., vortex rope formation and precession, is well captured using PANS simulations. The frequency of the vortex rope precession, which causes severe fluctuations and vibrations, is well predicted by only about 2.7% deviation from the experimental data. Finally, the physical mechanism behind the formation of the vortex rope is analyzed, and it is confirmed that the development of the vortex rope is associated with formation of a stagnant region at the center of the draft tube. Based on this observation, a vortex rope elimination method consisting of water jet injection to the draft tube is introduced and numerically assessed. It is shown that a small fraction of water (a few percent of the total flow rate) centrally injected to the inlet of the draft tube can eliminate the stagnant region and mitigate the formation of the vortex rope. This results in improvement of the draft tube performance and reduction of hydraulic losses. Specifically in the case of the simplified FLINDT draft tube, the loss coefficient can be reduced by as much as 50% and 14% when the turbine operates with 91% and 70% of the BEP flow rate, respectively. In addition, reduction (by about 1/3 in the case with 70% of BEP flow rate) of strong pressure fluctuations leads to more reliable operation of the turbine.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Turbine
Status
complete
Completion Date
2015
- Conventional Hydro
Solid State Processing for Improved Performance of current and Next Generation Hydro Components
Lead Companies
PNNL
Lead Researcher (s)
- Kenneth Ross
Completed projects with no scope descriptions
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Water Systems
Status
complete
Completion Date
2019
- Conventional Hydro
Stator Winding Temperature model
Lead Companies
Hydropower Research Institute
Lead Researcher (s)
- HRI Technical Steering Committee
This project is in the planning stage. The focus is on adapting existing, patented algorithm that predicts stator winding temperature based on other operational parameters to predicting temperature impacts from changing operational scenarios. This is in support of a request to an HRI participant to establish a value for a market product requested by a regulated market.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Status
ongoing
Completion Date
2021
- Conventional Hydro
Study of Mass Transfer across Hydrofoils for Use in Aerating Turbines
Lead Companies
University of Minnesota
Lead Researcher (s)
- Garrett Monson
Hydroelectric projects often have a low tailwater dissolved oxygen (DO) concentration. Low DO levels negatively impact the biota of the water body and are often regulated. Auto-Vented Turbines (AVTs) are one form of DO mitigation that is typically successful and cost-effective. Saint Anthony Falls Laboratory (SAFL) at the University of Minnesota (UMN) is partnering with the Department of Energy (DoE) and Alstom Engineering to conduct research developing a conventional hydropower turbine aeration test-bed for computational routines and a software tool for predicting the DO uptake of AVTs. The focus of this thesis is on the development of the testbed through the conduct of physical experiments focused on measuring mass transfer across bubbles in various flow conditions. This test-bed will be a valuable database for verification of numerical models of DO uptake. Numerical models can simulate the parameters of the water tunnel and experimental set-up, then verify their accuracy by simulating the air entrainment rate, bubble size and mass transfer of the test-bed. The findings presented herein can lead to further optimization of AVTs, as well as reduce cost and regulatory uncertainty prior to hydropower relicensing or development.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Turbine
Status
complete
Completion Date
2013
- Conventional Hydro
Surface-Reconditioning Additives Based on Solid Inorganic Nanoparticles for Environment-Friendly Industrial Lubricating Compositions
Lead Companies
Washington State University
Lead Researcher (s)
- Pavlo Rudenko
Our research is aimed at the application of lamellar ceramic solid nanoparticles as surface reconditioning additives to industrial lubricating oils to achieve self-repair and improve lubricity. According to a NERC, lubrication failures are among the top causes of outages and deratings of hydroelectric turbines. This problem represents a tremendous opportunity to improve the reliability and availability of hydroelectric turbines by improving their lubricating technologies. The majority of the environmental toxicity of these lubricating compositions is from the additives, where few alternative options are being explored. Today, the ability to formulate lubricating compositions that are safe for the environment greatly depends on additives. There has been a steadily growing interest toward solid, inorganic nanopowders of natural minerals such as Magnesium Hydro-Silicates(MHS) as antiwear and friction modifying additives in lubricating oils. Such powders can reduce wear and promote the formation of thick (up to 30 microns) tribofilms on the rubbing surfaces with great lubricating properties. Self-regulating mechanism of a film formation, and the ability to compensate for wear, allows for the self-repair effect to be achieved. This research is directed at expanding our understanding of the industrial applications for this technology and not only improve current lubricating compositions, but also note additional effects: such as superlubricity and reconditioning worn surfaces. We evaluated the influence of temperature, pressure, and concentration on friction properties. The optimal concentration of nanoparticles was obtained for steel-on-steel friction pairs. Our additives can be applied toward regular and preventative maintenance in the power generating industries as well as emergency surface treatment after lubrication failure has occured to compensate for wear.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Turbine
Status
complete
Completion Date
2013
- Conventional Hydro
The Impacts of Flexible Operation on Hydropower Assets: Generator
Lead Companies
EPRI
Lead Researcher (s)
- Francisco Kuljevan
With the increased penetration of variable renewable energy sources (wind and solar) in the electric grid’s energy mix, a greater need for a more flexible power system is required to maintain grid reliability. Hydropower has been shown to outpace its synchronous and inverter-base generation sources in a relative basis when providing the flexibility needed by the electric grid. Unfortunately, this flexibility comes with a potential decrease in fatigue life caused by the increased cycle activity, which was not accounted for when the assets were originally designed. With the use of electrical calculations, finite element analysis, and fatigue analysis, the study that is the subject of this report calculated the amplification damage factor caused by the flexible operation. The report focuses on two key generator components that have seen accelerated degradation caused by the change of operation patterns, from a baseload to a more flexible strategy.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Generator
Status
complete
Completion Date
2020
- Conventional Hydro
TIP 274: Development & Demonstration of Applications for BPA & FCRPS Compliance with Modeling Standards & Performance Monitoring
Lead Companies
BPA/US Army Corps of Engineers (USACE)
Lead Researcher (s)
- Steve Yang, BPA
The project developed and integrated a comprehensive set of power plant model validation and performance monitoring tools for BPA and US Army Corps of Engineers (USACE). It also developed capabilities at USACE to perform baseline testing and model validation needed to meet the WECC and BPA requirements.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Controls
Status
complete
Completion Date
2016
- Conventional Hydro
TIP 313: Power-Frequency Control
Lead Companies
BPA/US Army Corps of Engineers (USACE)/US Bureau of Reclamation (USBOR)
Lead Researcher (s)
- Dmitry Kosterev, BPA
The project researched technical approaches for the BPA to meet the NERC frequency response standards and reliability challenges. It built on the success of hydro-governor design and tuning work done under the existing TIP 50 research to develop plant control and Automatic Generation Control (AGC) strategies to meet diverse reliability objectives. By investigating relationships between frequency controls, angular stability, and voltage stability issues this project determined the benefits and feasibility of various technical strategies to address stability issues.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Controls
Status
complete
Completion Date
2017
- Conventional Hydro
TIP 346: Cold Spray Deposition for Improved Service Life of New and Repaired Hydroelectric Turbines
Lead Companies
Pacific Northwest National Laboratories /BPA
Lead Researcher (s)
- Dennis Mai, BPA
- Luke Chase, BPA
This project provides BPA and utilities with hydropower assets, a model that they can use to understand the value proposition of cold spray repair for their hydropower system. This tool calculates anticipated savings in terms of reduced downtime and increased efficiency. It generates data required for cold spray repair providers to quote the work. Using outputs from this model, utilities can perform costs analysis for a given turbine repair.
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Turbine
Status
complete
Completion Date
2019
- Conventional Hydro
TIP 350: Power Plant Dynamic Performance Monitoring Center
Lead Companies
BPA/USACE/US Bureau of Reclamation (USBOR)
Lead Researcher (s)
- Steve Yang, BPA
This project developed and demonstrated an integrated system for monitoring power plant dynamic performance and model validation. This system has the following capabilities: - Events are detected and classified, notifications are sent through the BPA e-mail, e-mail includes event report. Data is extracted automatically - Updates PPMV with State Estimator Models, upgraded to new API with GE PSLF that does not require use of external EPCLs - Automates model acceptance process similarly to PPMV process - Performs routine benchmarking of power plant performance against performance metrics such as Frequency Response Obligation and voltage control - Deploys small signal oscillation detection application, log events of sustained oscillations, and provides data extraction capabilities
Technology Application
Conventional Hydro
Research Category
Powerhouse Equipment
Research Sub-Category
Controls
Status
complete
Completion Date
2018
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Contact Marla Barnes at: marla@hydro.org