Thesis
The design and operation of X-rotor type wind turbines
- Creator
- Rights statement
- Awarding institution
- University of Strathclyde
- Date of award
- 2026
- Thesis identifier
- T18121
- Person Identifier (Local)
- 201984009
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- In order to successfully limit anthropogenic global heating, the rate of deployment for offshore wind energy needs to increase significantly over the coming decades. From an engineering perspective, this can be facilitated by a reduction in the cost of energy, and the avoidance of structural barriers to the installation of offshore wind energy. The X-Rotor is a vertical axis wind turbine concept that uses secondary rotors for power take-off. Studies have shown that this turbine concept has the potential to significantly decrease the cost of energy for offshore wind. The use of secondary rotors also reduces the required mass of rare earth metals, reducing the reliance on a geographically concentrated supply chain, and the use of a vertical axis primary rotor can also facilitate an increase in wind farm density, easing the constraints on site availability. This thesis investigates the design and operation of X-Rotor type turbines, understanding the dynamics of power take-off with secondary rotors, the design of both primary and secondary rotors, and the operation of X-Rotor type turbines. The aerodynamic aspects of power take-off with secondary rotors are derived, treating the secondary rotor as both an actuator disk and an optimally designed rotor. It is found that conversion efficiencies between the primary and secondary rotors of between 80%-85% are achievable, relying on low induction secondary rotors and high primary rotor tip speeds. The design of high tip speed ratio VAWTs is then investigated, and it is shown that the use of straight bladed VAWTs with blades incline to the vertical plane can increase both the optimum tip speed ratio and the maximum power available to the primary rotor. The design of an X-Rotor type turbine is then completed coupling the optimum secondary rotor design process with a large sample of primary rotor designs. It is shown that an inclination angle is necessary to achieve a 5MW 2 bladed design with an unsupported blade length less than 100m, and that a minimum blade of 78m is required, using a blade chord length of 5m and an inclination angle of 30 degrees. It is found that the use of inclined blades reduces the maximum operational thrust, operational out of blade root bending moment, and the extreme blade root bending moment for rotors with equivalent power ratings. Rotor designs which minimise the combined blade mass of the upper and lower blades, whilst achieving a power rating of 5MW at 12m/s are identified to have chord lengths between 4m-6m, blade lengths of 78m-80m, and inclination angles between 30◦ and 40◦. Finally, the control of X-Rotor type wind turbines is investigated. The maximum power coefficient of the 5MW 2 bladed X-Rotor design, investigated as part of the Horizon 2020 X-Rotor project, including the conversion of power between the primary and secondary rotors is calculated to be 0.41. Following this, a recommended operational strategy for the 5MW 2 bladed X-Rotor design is presented which ensures high conversion efficiency at low wind speeds, limits power capture in above rated wind speeds, and conforms to strict limits on secondary rotor speed.
- Advisor / supervisor
- Leithead, Bill
- Carroll, James
- Resource Type
- DOI
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PDF of thesis T18121 | 2026-10-27 | Public | Download |