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Aerodynamic Studies of Vertical Axis Wind Turbines using the Actuator Line Model
Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.ORCID iD: 0000-0001-5006-9231
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis addresses the unsteady aerodynamics involved in the operation of vertical axis wind turbines (VAWTs). The main focus is to represent and understand the most relevant phenomena within the resulting flow pattern as the wake structure, loads on the different turbine components and the performance of the rotor. An actuator line model has been used for this purpose.

This model has been validated against experimental measurements from diverse cases with different operating conditions in both confined wind tunnels and open site locations. Numerical works were carried out considering a wide range of tip speed ratios (TSRs), and therefore covering from the no stall to the deep stall regime. The latter requires the implementation of a dynamic stall model for the proper representation of the unsteady forces on the blades. Also, different inlet conditions such as a uniform flow, a logarithmic wind shear and an atmospheric boundary layer (ABL) have been tested. The so-called recycling method technique was used to produce the fully developed ABL flow. Additionally, the resulting wake and performance of interacting turbines has been studied.

Once the model was validated, two numerical study cases for large scale turbines were carried out. First, the performance and resulting flow field from both a horizontal axis wind turbine (HAWT) and VAWT were investigated when the turbines were operating at their optimal TSR and within the same ABL inflow boundary conditions. The influence of the variation on the atmospheric turbulence levels was also studied, as well as the differences and similarities on the obtained results for both type of turbines. Later, the performance improvement of two interacting VAWTs was investigated through the deflected wake produced by the pitched struts of the upstream turbine. This is presented as a novel mechanism to mitigate losses on interacting turbine arrangements (i.e. wind farms).

In general, there is a reasonable good agreement between numerical results and experimental measurements, and therefore, the applied ALM can be considered as a potential tool for VAWTs simulations, characterized by relatively low computational cost showing accuracy and numerical stability.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. , p. 85
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1671
Keywords [en]
wind power, vertical axis wind turbines (VAWTs), actuator line model (ALM), dynamic stall model (DSM), atmospheric boundary layer (ABL), wake deflection, atmospheric boundary layer (ABL)
National Category
Engineering and Technology
Research subject
Engineering Science with specialization in Science of Electricity
Identifiers
URN: urn:nbn:se:uu:diva-348346ISBN: 978-91-513-0338-3 (print)OAI: oai:DiVA.org:uu-348346DiVA, id: diva2:1197101
Public defence
2018-06-05, Häggsalen, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 09:00 (English)
Opponent
Supervisors
Funder
StandUp for WindAvailable from: 2018-05-15 Created: 2018-04-11 Last updated: 2018-10-08
List of papers
1. Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines
Open this publication in new window or tab >>Validation of an Actuator Line Model Coupled to a Dynamic Stall Model for Pitching Motions Characteristic to Vertical Axis Turbines
2016 (English)In: Science Of Making Torque From Wind (Torque 2016) / [ed] IOP, 2016, article id 022043Conference paper, Published paper (Refereed)
Abstract [en]

Vertical axis wind turbines (VAWT) can be used to extract renewable energy from wind flows. A simpler design, low cost of maintenance, and the ability to accept flow from all directions perpendicular to the rotor axis are some of the most important advantages over conventional horizontal axis wind turbines (HAWT). However, VAWT encounter complex and unsteady fluid dynamics, which present significant modeling challenges. One of the most relevant phenomena is dynamic stall, which is caused by the unsteady variation of angle of attack throughout the blade rotation, and is the focus of the present study. Dynamic stall is usually used as a passive control for VAWT operating conditions, hence the importance of predicting its effects. In this study, a coupled model is implemented with the open-source CFD toolbox OpenFOAM for solving the Navier-Stokes equations, where an actuator line model and dynamic stall model are used to compute the blade loading and body force. Force coefficients obtained from the model are validated with experimental data of pitching airfoil in similar operating conditions as an H-rotor type VAWT. Numerical results show reasonable agreement with experimental data for pitching motion.

Series
Journal of Physics Conference Series, ISSN 1742-6588, E-ISSN 1742-6596 ; 753
National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-305170 (URN)10.1088/1742-6596/753/2/022043 (DOI)000436325700043 ()
Conference
The Science of Making Torque from Wind (TORQUE 2016),OCT 05-07, 2016, Munich, Germany
Funder
StandUp for Wind
Available from: 2016-10-12 Created: 2016-10-12 Last updated: 2020-01-07Bibliographically approved
2. Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear
Open this publication in new window or tab >>Wake Flow Simulation of a Vertical Axis Wind Turbine Under the Influence of Wind Shear
2017 (English)In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 854, article id 012031Article in journal (Refereed) Published
Abstract [en]

The current trend of the wind energy industry aims for large scale turbines installed in wind farms. This brings a renewed interest in vertical axis wind turbines (VAWTs) since they have several advantages over the traditional Horizontal Axis Wind Tubines (HAWTs) for mitigating the new challenges. However, operating VAWTs are characterized by complex aerodynamics phenomena, presenting considerable challenges for modeling tools. An accurate and reliable simulation tool for predicting the interaction between the obtained wake of an operating VAWT and the flow in atmospheric open sites is fundamental for optimizing the design and location of wind energy facility projects. The present work studies the wake produced by a VAWT and how it is affected by the surface roughness of the terrain, without considering the effects of the ambient turbulence intensity. This study was carried out using an actuator line model (ALM), and it was implemented using the open-source CFD library OpenFOAM to solve the governing equations and to compute the resulting flow fields. An operational H-shaped VAWT model was tested, for which experimental activity has been performed at an open site north of Uppsala-Sweden. Different terrains with similar inflow velocities have been evaluated. Simulated velocity and vorticity of representative sections have been analyzed. Numerical results were validated using normal forces measurements, showing reasonable agreement.

National Category
Energy Engineering
Identifiers
urn:nbn:se:uu:diva-348342 (URN)10.1088/1742-6596/854/1/012031 (DOI)000435276400031 ()
Conference
Wake Conference, MAY 30-JUN 01, 2017, Uppsala Univ Gotland Campus, Visby, SWEDEN
Funder
StandUp for Wind
Available from: 2018-04-11 Created: 2018-04-11 Last updated: 2018-11-23Bibliographically approved
3. Near-Wake Flow Simulation of a Vertical Axis Turbine Using an Actuator Line Model
Open this publication in new window or tab >>Near-Wake Flow Simulation of a Vertical Axis Turbine Using an Actuator Line Model
2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 2, p. 171-188Article in journal (Refereed) Published
Abstract [en]

In the present work, the near‐wake generated for a vertical axis wind turbine (VAWT) was simulated using an actuator line model (ALM) in order to validate and evaluate its accuracy. The sensitivity of the model to the variation of the spatial and temporal discretization was studied and showed a bigger response to the variation in the mesh size as compared with the temporal discretization. The large eddy simulation (LES) approach was used to predict the turbulence effects. The performance of Smagorinsky, dynamic k‐equation, and dynamic Lagrangian turbulence models was tested, showing very little relevant differences between them. Generally, predicted results agree well with experimental data for velocity and vorticity fields in representative sections. The presented ALM was able to characterize the main phenomena involved in the flow pattern using a relatively low computational cost without stability concerns, identified the general wake structure (qualitatively and quantitatively), and the contribution from the blade tips and motion on it. Additionally, the effects of the tower and struts were investigated with respect to the overall structure of the wake, showing no significant modification. Similarities and discrepancies between numerical and experimental results are discussed. The obtained results from the various simulations carried out here can be used as a practical reference guideline for choosing parameters in VAWTs simulations using the ALM.

Keywords
actuator line model, dynamic stall model, near wake simulation, vawt, vertical axis wind turbine
National Category
Energy Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:uu:diva-348688 (URN)10.1002/we.2277 (DOI)000455955800002 ()
Funder
StandUp for Wind
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-02-05Bibliographically approved
4. Validation of Actuator Line and Vortex Models using Normal Forces Measurements of a Straight-Bladed Vertical Axis Wind Turbine
Open this publication in new window or tab >>Validation of Actuator Line and Vortex Models using Normal Forces Measurements of a Straight-Bladed Vertical Axis Wind Turbine
2020 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 13, no 3, article id 511Article in journal (Refereed) Published
Abstract [en]

Vertical Axis Wind Turbines (VAWTs) are characterized by complex and unsteady flow patterns resulting in considerable challenges for both numerical simulations and measurements describing the phenomena involved. In this study, a 3D Actuator Line Model (ALM) is compared to a 2D and a 3D Vortex Model, and they are validated using the normal forces measurements on a blade of an operating 12 kW VAWT, which is located in an open site in the north of Uppsala, Sweden. First, the coefficient power ( Cp ) curve of the device has been simulated and compared against the experimental one. Then, a wide range of operational conditions for different tip speed ratios (TSRs), with λ = 1.84, 2.55, 3.06, 3.44, 4.09 and 4.57 were investigated. The results showed descent agreement with the experimental data for both models in terms of the trend and magnitudes. On one side, a slight improvement for representing the normal forces was achieved by the ALM, while the vortex code performs better in the simulation of the Cp curve. Similarities and discrepancies between numerical and experimental results are discussed.

Keywords
vertical axis wind turbines, actuator line model, vortex method, dynamic stall model
National Category
Other Environmental Engineering
Identifiers
urn:nbn:se:uu:diva-348689 (URN)10.3390/en13030511 (DOI)000522489000005 ()
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2020-05-08Bibliographically approved
5. Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions
Open this publication in new window or tab >>Performance and wake comparison of horizontal and vertical axis wind turbines under varying surface roughness conditions
2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 458-472Article in journal (Refereed) Published
Abstract [en]

A numerical study of both a horizontal axis wind turbine (HAWT) and a vertical axis wind turbine (VAWT) with similar size and power rating is presented. These large scale turbines have been tested when operating stand-alone at their optimal tip speed ratio (TSR) within a neutrally stratified atmospheric boundary layer (ABL). The impact of three different surface roughness lengths on the turbine performance is studied for the both turbines. The turbines performance, the response to the variation in the surface roughness of terrain, and the most relevant phenomena involved on the resulting wake were investigated. The main goal was to evaluate the differences and similarities of these two different types of turbine when they operate under the same atmospheric flow conditions. An actuator line model (ALM) was used together with the large eddy simulation (LES) approach for predicting wake effects, and it was implemented using the open-source computational fluid dynamics (CFD) library OpenFOAM to solve the governing equations and to compute the resulting flow fields. This model was first validated using wind tunnel measurements of power coefficients and wake of interacting HAWTs, and then employed to study the wake structure of both full scale turbines. A preliminary study test comparing the forces on a VAWT blades against measurements was also investigated. These obtained results showed a better performance and shorter wake (faster recovery) for an HAWT compared with a VAWT for the same atmospheric conditions.

National Category
Fluid Mechanics and Acoustics Energy Engineering
Identifiers
urn:nbn:se:uu:diva-348690 (URN)10.1002/we.2299 (DOI)000461904600002 ()
Funder
StandUp for Wind
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-05-07Bibliographically approved
6. Improving farm efficiency of interacting vertical‐axis wind turbines through wake deflection using pitched struts
Open this publication in new window or tab >>Improving farm efficiency of interacting vertical‐axis wind turbines through wake deflection using pitched struts
2019 (English)In: Wind Energy, ISSN 1095-4244, E-ISSN 1099-1824, Vol. 22, no 4, p. 538-546Article in journal (Refereed) Published
Abstract [en]

This work presents a numerical study of the obtained performance and the resulting flow field between two interacting large scale vertical-axis wind turbines (VAWTs), under the influence of a deflected wake through the struts pitching of the upwind turbine. The configuration consists of two VAWTs aligned in the direction of the incoming flow in which a wide range of fixed struts pitching angles in the upwind turbine have been investigated. The main goal is to evaluate the influence of the wake deflection on the turbines performance while they are operating at their optimal tip speed ratio (TSR), and to reproduce the most relevant phenomena involved in the flow pattern of the interacting wake. Arrangements with cross-stream offsets have also been tested for quantifying the contribution of this modification into the overall performance. For this purpose, an actuator line model (ALM) has been implemented using the open-source CFD library OpenFOAM in order to solve the governing equations and to calculate the resulting flow. The Large eddy simulation (LES) approach is considered to reproduce the turbulence flow effects. A preliminary study to identify the optimal TSR of the interacting downwind turbine has been investigated.

Keywords
actuator line model (ALM), dynamic stall model (DSM), large eddy simulation (LES), vertical axis wind turbines (VAWTs), wake deflection
National Category
Energy Engineering Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:uu:diva-348692 (URN)10.1002/we.2305 (DOI)000461904600008 ()
Funder
StandUp for Wind
Available from: 2018-04-17 Created: 2018-04-17 Last updated: 2019-05-07Bibliographically approved

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Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
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  • de-DE
  • en-GB
  • en-US
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  • nn-NO
  • nn-NB
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  • Other locale
More languages
Output format
  • html
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