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A sensitivity analysis of the Winter-Kennedy method
Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.ORCID iD: 0000-0001-5833-6736
2018 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Hydropower is among the lowest-cost electrical energy sources due to its long lifespan and lower operation and maintenance cost. The hydro-mechanical components of hydropower plants generally last about four to five decades, then they are either overhauled or replaced. The major upgrades and refurbishments of the hydropower plants that are ongoing have also been motivated by the introduction of new rules and regulations, safety or environmentally friendly and improved turbine designs. Whatever are the drivers, the refurbishments are usually expected to increase efficiency, flexibility and more power from the plant.

Efficiency measurement is usually performed after refurbishments. While it is relatively straightforward to measure efficiency in high head machines due to the availability of several code-accepted methods, similar measurements in low head plants remain a challenge. The main difficulty lies in the discharge/flow rate measurement. The reason is due to the continuously varying cross-section and short intake, as a result, the flow profile or parallel streamlines cannot be established. Among several relative methods, the Winter-Kennedy (WK) method is widely used to determine the step-up efficiency before and after refurbishment. The WK method is an index testing approach allowing to determine the on-cam relationship between blade and guide vane angles for Kaplan turbine as well. The method utilizes features of the flow physics in a curvilinear motion. A pair of pressure taps is placed at an inner and outer section of the spiral case (SC). The method relates discharge (Q) as Q=K(dP)^n, where K is usually called as the WK constant and n is the exponent whose value varies from 0.48 to 0.52. dP is the differential pressure from the pair of pressure taps placed on the SC.  

Although the method has very high repeatability, some discrepancies were noticed in previous studies. The reasons are often attributed to the change in local flow conditions due to the change in inflow conditions, corrosions, or change in geometry. Paper A is a review of the WK method, which includes the possible factors that can influence the WK method. Considering the possible factors, the aim of this thesis is to study the change in flow behavior and its impact on the coefficients. Therefore, a numerical model of a Kaplan turbine has been developed. The turbine model of Hölleforsen hydropower plant in Sweden was used in the study. The plant is considered as a low head with 27-m head and a discharge of 230 m3/s. The 1:11 scale model of the prototype is used as the numerical model in this study, which has 0.5 m runner diameter, 4.5 m head, 0.522 m3/s discharge and 595 rpm at its best efficiency point. A sensitivity analysis of the WK method has been performed with the help of CFD simulations. The numerical results are compared with the previously conducted experiment on the model. The study considers four different WK configurations at seven locations along the azimuthal direction. The simulations have been performed with different inlet boundary conditions (Paper B and Paper C) and different runner blade angles (Paper C). The CFD results show that the WK coefficients are sensitive to inlet conditions. The study also concludes that to limit the impact of a change in inflow conditions, runner blade angle on the coefficients, the more suitable WK locations are at the beginning of the SC with the inner pressure tap placed between stay vanes on the top wall.

Place, publisher, year, edition, pages
Luleå: Luleå University of Technology, 2018.
Series
Licentiate thesis / Luleå University of Technology, ISSN 1402-1757
Keywords [en]
Hydropower, discharge, Winter-Kennedy, CFD, Sensitivity
National Category
Fluid Mechanics and Acoustics Energy Engineering
Research subject
Fluid Mechanics
Identifiers
URN: urn:nbn:se:ltu:diva-70157ISBN: 978-91-7790-176-1 (print)ISBN: 978-91-7790-177-8 (electronic)OAI: oai:DiVA.org:ltu-70157DiVA, id: diva2:1235247
Presentation
2018-10-05, E246, Luleå, 13:00 (English)
Opponent
Supervisors
Available from: 2018-07-31 Created: 2018-07-24 Last updated: 2018-07-31Bibliographically approved
List of papers
1. Winter-Kennedy method in hydraulic discharge measurement: Problems and Challenges
Open this publication in new window or tab >>Winter-Kennedy method in hydraulic discharge measurement: Problems and Challenges
2016 (English)Conference paper, Published paper (Refereed)
Abstract [en]

Winter Kennedy (WK) method is a popular way to measure the relative discharge and thus efficiency in Swedish hydropower plants. This is largely motivated by the numerous low head turbines and low cost of the method. WK is an index testing method that provides relative values of hydraulic efficiency by measuring differential pressures in one or two pairs of pressure taps in radial planes of the spiral casing. The method is described in the IEC41 standard. Despite several limitations, it is generally used to verify the increment in efficiency for refurbishment projects and sometimes for the continuous flow rate monitoring. Uncertainties in the results reaching up to 5% have been reported in different researches. Those are often attributed to a change in flow conditions after the refurbishment or in the course of time. However, a proper error analysis has not been performed yet. This paper includes a review of the available literature related to the topic to understand its problems and possible ways to investigate its limitations systematically.

National Category
Energy Engineering Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-65053 (URN)
Conference
11th International conference on hydraulic efficiency measurement (IGHEM2016), Linz, Austria, 24-26 August, 2016
Available from: 2017-08-14 Created: 2017-08-14 Last updated: 2018-07-24Bibliographically approved
2. Numerical study of the Winter-Kennedy method: a sensitivity analysis
Open this publication in new window or tab >>Numerical study of the Winter-Kennedy method: a sensitivity analysis
2018 (English)In: Journal of Fluids Engineering - Trancactions of The ASME, ISSN 0098-2202, E-ISSN 1528-901X, Vol. 140, no 5, article id 051103Article in journal (Refereed) Published
Abstract [en]

The Winter-Kennedy (WK) method is commonly used in relative discharge measurement and to quantify efficiency step-up in hydropower refurbishment projects. The method utilizes the differential pressure between two taps located at a radial section of a spiral case, which is related to the discharge with the help of a coefficient and an exponent. Nearly a century old and widely used, the method has shown some discrepancies when the same coefficient is used after a plant upgrade. The reasons are often attributed to local flow changes. To study the change in flow behavior and its impact on the coefficient, a numerical model of a semi-spiral case (SC) has been developed and the numerical results are compared with experimental results. The simulations of the SC have been performed with different inlet boundary conditions. Comparison between an analytical formulation with the computational fluid dynamics (CFD) results shows that the flow inside an SC is highly three-dimensional (3D). The magnitude of the secondary flow is a function of the inlet boundary conditions. The secondary flow affects the vortex flow distribution and hence the coefficients. For the SC considered in this study, the most stable WK configurations are located toward the bottom from θ =30deg to 45deg after the curve of the SC begins, and on the top between two stay vanes.

Place, publisher, year, edition, pages
ASME Press, 2018
Keywords
Winter-Kennedy, Discharge, hydropower, Spiral-case
National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-66441 (URN)10.1115/1.4038662 (DOI)000427848100010 ()2-s2.0-85044437186 (Scopus ID)
Note

Validerad;2018;Nivå 2;2018-04-06 (svasva)

Available from: 2017-11-07 Created: 2017-11-07 Last updated: 2018-07-24Bibliographically approved
3. Sensitivity of the Winter-Kennedy method to inlet and runner blade angle change on a Kaplan turbine
Open this publication in new window or tab >>Sensitivity of the Winter-Kennedy method to inlet and runner blade angle change on a Kaplan turbine
2018 (English)In: IOP Conference Series: Earth and Environment, ISSN 1755-1307, E-ISSN 1755-1315Article in journal (Refereed) Accepted
Abstract [en]

The Winter-Kennedy (WK) method is a widely used index testing approach, which provides a relative or index value of the discharge that can allow to determine the on-cam relationship between blade and guide vane angles for Kaplan turbines. However, some discrepancies were noticed in previous studies using the WK approach. In this paper, a numerical model of a Kaplan model turbine is used to study the effects of upstream and downstream flow conditions on the WK coefficients. Experiment on the model turbine is used to validate unsteady CFD calculations. The CFD results show that the inflow condition affects the pressure distribution inside the spiral case and hence the WK results. The WK coefficients fluctuate with high amplitude - suggesting to use a larger sampling time for on-site measurement as well. The study also concludes that to limit the impact of a change in runner blade angle on the coefficients, the more suitable WK locations are at the beginning of the spiral case with the inner pressure tap placed between stay vanes on the top wall.

National Category
Fluid Mechanics and Acoustics
Research subject
Fluid Mechanics
Identifiers
urn:nbn:se:ltu:diva-70147 (URN)
Conference
29th IAHR Symposium on Hydraulic Machinery and Systems, Kyoto, September 16-21, 2018
Available from: 2018-07-24 Created: 2018-07-24 Last updated: 2018-08-14

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