Thesis
Aerodynamic modelling and control of vertical axis wind turbines
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2014
- Thesis identifier
- T13728
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- Designing a structure which harnesses energy from the wind offshore is a radically different design challenge compared to that which the industry standard three-blade Danish model horizontal axis wind turbine (HAWT) has evolved to serve. Vertical axis wind turbines (VAWTs) may prove to be suitable candidates for the offshore sector due to the potential to locate heavy and complex mechanical components near the water surface providing ease of access and a low centre of gravity. Unlike their horizontal-axis counterparts, VAWT designs have not benefited from forty years of intense research and development. Therefore many challenges lie ahead for VAWT technology but lessons can be drawn from the development of HAWT technology. The main aims of this thesis are to create a design tool capable of investigating the performance of large scale, variable pitch VAWTs and to provide analyses of rotor design and control systems that would align utility scale VAWTs with aerodynamic performance and operational flexibility of state of the art HAWTs. The design tool developed is based on the double multiple streamtube (DMS) adaptation of blade element momentum theory and it incorporates tip loss effects, flow curvature, dynamic stall, flow expansion and variable pitch. Validation demonstrates good estimation of local wind flow conditions and aerodynamic performance for both fixed pitch and variable pitch rotors. The model has been developed to investigate in particular V-rotor performance and the potential of variable pitch for VAWTs. A contribution is made to DMS modelling, which involves capturing the effects of varying degrees of streamtube expansion occurring along the blade. This contribution is referred to as fanning and is particularly significant when implementing or designing pitch regimes. Three novel investigations are provided that contribute to fixed pitch VAWT rotor design and control. Firstly, a method for applying lift to drag ratio to VAWTs is introduced, which accounts for azimuthal variation in aerodynamic performance. Secondly, the impact of wind shear on V-rotor rotor design is analysed. Thirdly, a solution for smoothing power fluctuations from aggregated VAWTs is proposed, which is based on controlling the phase of each rotor so peaks in individual generated power do not occur simultaneously. A holistic approach to the way in which cyclic variable pitch can benefit VAWT operation is provided. Five control objectives are identified that span the entire operating envelope for any wind turbine, namely providing high torque during start-up, maximising power coefficient in below rated conditions, alleviating cyclic loading, power limiting in above rated conditions and aerodynamic braking in extremely high winds. Two test case turbines are designed, a similarly rated H-rotor and V-rotor, and for each turbine and each objective, a cyclic pitch regime is developed and analysed.
- Resource Type
- DOI
- Date Created
- 2014
- Former identifier
- 1032518
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