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Vertical Axis Wind Turbines: Tower Dynamics and Noise
Halmstad University, School of Business, Engineering and Science, Biological and Environmental Systems (BLESS), Energiteknik.ORCID iD: 0000-0001-9982-5317
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Vertical axis wind turbines (VAWTs) have with time been outrivaled by the today common and economically feasible horizontal axis wind turbines (HAWTs). However, VAWTs have several advantages such as the possibility to put the drive train at ground level, lower noise emissions and better scaling behavior which still make them interesting for research.

The work within this thesis is made in collaboration between the Department of Construction and Energy Engineering at Halmstad University and the Division for Electricity at Uppsala University. A 200 kW VAWT owned by the latter and situated close to Falkenberg in the southwest of Sweden has been the main subject of the research even if most learnings has been generalized to fit a typical vertical turbine. This particular turbine has a wooden tower which is semi-guy-wired, i.e. the tower is both firmly attached to the ground and supported by guy-wires.

This thesis has two main topics both regarding VAWTs: eigenfrequency of the tower and the noise generated from the turbine. The eigenfrequency of a semi-guy-wired tower is studied and an analytical expression describing this is produced and verified by experiments and simulations. The eigenfrequency of the wire itself and how it is affected by wind load are also studied.  The noise characteristics of VAWTs have been investigated, both theoretically and by noise measurement campaigns. Both noise emission and frequency distribution of VAWTs has been studied.

The work has resulted in analytical expressions for tower and wire eigenfrequency of a semi-guy-wired tower as well as recommendations for designing future towers for VAWTs. The noise emission of VAWTs has been studied and proven low compared to HAWTs. The noise frequency distribution of the 200 kW VAWT differs significantly from that of a similar size HAWTs with for example lower levels for frequencies below 3000 Hz.

Place, publisher, year, edition, pages
Uppsala: Uppsala universitet, 2015. , 61 p.
Series
UURIE / Uppsala universitet, Institutitionen för teknikvetenskaper, ISSN 0349-8352 ; 340-15L
Keyword [en]
VAWT, H-rotor, eigenfrequency, semi-guy-wired tower, noise emission, sound power level
National Category
Energy Engineering
Identifiers
URN: urn:nbn:se:hh:diva-27526OAI: oai:DiVA.org:hh-27526DiVA: diva2:781905
Presentation
2015-01-16, Polhemsalen, Ångströmlaboratoriet, Uppsala, 13:43 (English)
Opponent
Supervisors
Funder
StandUp
Available from: 2015-01-22 Created: 2015-01-19 Last updated: 2015-02-18Bibliographically approved
List of papers
1. Eigen Frequencies of A Vertical Axis Wind Turbine Tower Made of Laminated Wood and the Effect Upon Attaching Guy Wires
Open this publication in new window or tab >>Eigen Frequencies of A Vertical Axis Wind Turbine Tower Made of Laminated Wood and the Effect Upon Attaching Guy Wires
2014 (English)In: Wind Engineering: The International Journal of Wind Power, ISSN 0309-524X, E-ISSN 2048-402X, Vol. 38, no 3, 277-290 p.Article in journal (Refereed) Published
Abstract [en]

Eigen frequencies of a vertical axis wind turbine tower made out of laminated wood which are both bolted to the ground and supported by guy wires are studied and compared. Using beam theory, an analytical model taking the guy wires into account for calculating the first mode eigen frequency of the tower has been derived. The analytical model is then evaluated by comparing with FEM-simulations and measurements performed on the actual tower. The model is found to be reasonably accurate keeping in mind that the estimated masses and second moments of area are somewhat rough. Furthermore the model can be used to give an indication of the magnitude of change in eigen frequency when modifying a tower or guy wire property.

Place, publisher, year, edition, pages
Brentwood, United Kingdom: Multi-Science Publishing, 2014
Keyword
VAWT, Vertical Axis Wind Turbine, Semi-guy-wired, Natural frequency, Eigen frequency, Resonance
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-25467 (URN)10.1260/0309-524X.38.3.277 (DOI)2-s2.0-84901792518 (Scopus ID)
Funder
StandUp
Available from: 2014-06-02 Created: 2014-06-02 Last updated: 2017-05-10Bibliographically approved
2. Avoidance of resonances in a semi-guy-wired vertical axis wind turbine
Open this publication in new window or tab >>Avoidance of resonances in a semi-guy-wired vertical axis wind turbine
2014 (English)Conference paper, (Refereed)
Abstract [en]

Resonance analysis for a vertical axis wind turbine is performed. The turbine may be described as semi-guy wired, being bolted stiffly to the ground as well as supported by guy wires. The influence of the first mode eigen frequency of the guy wires and how it is affected by wind load is examined. Using beam theory, an analytical model for calculating the first mode eigen frequency of the guy wire for different wind loads is derived. The analytical model is verified with FEM-simulations and then used to assemble a diagram showing how to combine the wire size, inclination angle and pre-tension for an eigen frequency range over the 3P load for nominal rotational speed and for a certain effective spring force acting on the tower. This diagram, here called an EA-T diagram, may be used as a quick tool for comparing wire setups and a similar diagram can be used for other guy wired structures.

Keyword
VAWT, guy wire, semi-guy-wired, resonance, eigen frequency, natural frequency
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-24884 (URN)
Conference
EWEA 2014 - European Wind Energy Association – Annual Event (Conference), Barcelona, Spain, 10-13 March, 2014
Funder
StandUp
Available from: 2014-03-19 Created: 2014-03-19 Last updated: 2017-05-10Bibliographically approved
3. Noise Propagation from a Vertical Axis Wind Turbine
Open this publication in new window or tab >>Noise Propagation from a Vertical Axis Wind Turbine
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2014 (English)In: Proceedings of 43rd International Congress on Noise Control Engineering: Internoise 2014 / [ed] John Davy, Charles Don, Terry McMinn, Liz Dowsett, Norm Broner & Marion Burgess, Brisbane, QLD: Australian Acoustical Society , 2014Conference paper, (Refereed)
Abstract [en]

Initial noise measurements were performed on a 200kW vertical axis wind turbine (VAWT) and results were compared to that of a Vestas V27, a similar size horizontal axis wind turbine (HAWT). Multiple recording units were placed in line downwind of the turbine to investigate noise propagation. The frequency distribution of the noise were analyzed indicating that the VAWT has lower relative levels for frequencies under 3000 Hz, especially within 600-1200 Hz. Furthermore, VAWT noise seems to occur more around the same frequencies as the natural background noise, increasing masking probability. Results from propagation measurements seemed to indicate that noise declines more rapidly with distance for the VAWT then for the reference HAWT, possibly explained by the lower levels at low frequencies. Further investigation is needed to establish these differences and the 200 kW VAWT creates an opportunity doing so utilizing arguably the largest operational VAWT existing today.

Place, publisher, year, edition, pages
Brisbane, QLD: Australian Acoustical Society, 2014
Keyword
VAWT, Wind Turbine, Propagation
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-27107 (URN)2-s2.0-84923595295 (Scopus ID)978-0-909882-02-0 (ISBN)978-0-909882-03-7 (ISBN)978-0-909882-04-4 (ISBN)
Conference
inter.noise 2014, 43rd International Congress on Noise Control Engineering, Melbourne, Australia, November 16-19, 2014
Funder
StandUp
Available from: 2014-11-25 Created: 2014-11-25 Last updated: 2017-05-10Bibliographically approved
4. Noise Emission of a 200 kW Vertical Axis Wind Turbine
Open this publication in new window or tab >>Noise Emission of a 200 kW Vertical Axis Wind Turbine
2016 (English)In: Energies, ISSN 1996-1073, E-ISSN 1996-1073, Vol. 9, no 1, 19Article in journal (Refereed) Published
Abstract [en]

The noise emission from a vertical axis wind turbine (VAWT) has been investigated. A noisemeasurement campaign on a 200 kW straight-bladed VAWT has been conducted, and the result hasbeen compared to a semi-empirical model for turbulent-boundary-layer trailing edge (TBL-TE) noise.The noise emission from the wind turbine was measured, at wind speed 8 m/s, 10 m above ground, to96.2 dBA. At this wind speed, the turbine was stalling as it was run at a tip speed lower than optimaldue to constructional constraints. The noise emission at a wind speed of 6 m/s, 10 m above groundwas measured while operating at optimum tip speed and was found to be 94.1 dBA. A comparisonwith similar size horizontal axis wind turbines (HAWTs) indicates a noise emission at the absolutebottom of the range. Furthermore, it is clear from the analysis that the turbulent-boundary-layertrailing-edge noise, as modeled here, is much lower than the measured levels, which suggests thatother mechanisms are likely to be important, such as inflow turbulence.

Place, publisher, year, edition, pages
Basel: MDPI, 2016
Keyword
vertical axis wind turbine (VAWT), H-rotor, noise, noise emission, sound power level
National Category
Energy Engineering
Identifiers
urn:nbn:se:hh:diva-27523 (URN)10.3390/en9010019 (DOI)
Funder
StandUp
Available from: 2015-01-19 Created: 2015-01-19 Last updated: 2017-05-10Bibliographically approved

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