Renewable Energy

Performance enhancements from closely spaced vertical axis wind turbines

Supervisor: Dr Andrew Shires

Project Summary: Wind power generation is the fastest growing source of energy in the world today with global warming, energy security and rising fuel prices being main public concerns. However, reducing the cost of electricity (CoE) from wind power to be competitive with fossil fuel energy sources is a significant challenge, particularly for offshore wind. The main driver in reducing CoE since the beginning of the commercial wind industry has been increasing turbine rotor size. However, conventional horizontal axis wind turbine (HAWT) blades have size limitations, particularly due to self-weight induced fatigue loading. These turbines also have a number of other limitations for offshore operations, particularly in deep water (i.e. over 50m) such as;  the necessity for high lift installations offshore requiring specialist vessels, high gravitational and aerodynamic moments on the support structure and a need to maintain rotary equipment at heights typically over 60-80m. Consequently there has been a resurgence of interest in the development of vertical axis wind turbines (VAWTs) which have several inherent attributes that offer some advantages for offshore operations, particularly their scalability and low over-turning moments with better accessibility to drivetrain components. Unfortunately however, VAWTs generally have a lower aerodynamic efficiency than an equivalent sized HAWT, which has a significant impact increasing the CoE.

Tasks and expected milestones/deliverables: Research has suggested that closely-spaced contra-rotating VAWTs can increase energy capture by around 10-20% relative to an isolated VAWT. This proposed research will develop a thorough understanding of VAWT aerodynamic behaviour and, in particular, the interaction between closely spaced VAWTs to assess and quantify these potential benefits. It will propose validated design methodologies that can be exploited by wind turbine manufacturers to reduce the CoE through advanced designs. The research will use a combination of high fidelity Computational Fluid Dynamic (CFD) simulations and wind turbine rotor performance as well as blade element momentum models.

Performance enhancements of vertical axis wind turbines using cyclic load control

Supervisor: Dr Andrew Shires

Project Summary: Wind power generation is the fastest growing source of energy in the world today with global warming, energy security and rising fuel prices being main public concerns. However, reducing the cost of electricity (CoE) from wind power to be competitive with fossil fuel energy sources is a significant challenge, particularly for offshore wind. The main driver in reducing CoE since the beginning of the commercial wind industry has been increasing turbine rotor size. However, conventional horizontal axis wind turbine (HAWT) blades have size limitations, particularly due to self-weight induced fatigue loading. These turbines also have a number of other limitations for offshore operations, particularly in deep water (i.e. over 50m) such as;  the necessity for high lift installations offshore requiring specialist vessels, high gravitational and aerodynamic moments on the support structure and a need to maintain rotary equipment at heights typically over 60-80m. Consequently there has been a resurgence of interest in the development of vertical axis wind turbines (VAWTs) which have several inherent attributes that offer some advantages for offshore operations, particularly their scalability and low over-turning moments with better accessibility to drivetrain components. However, unlike the operation of a HAWT rotor a VAWT rotor blade sees an inconsistent angle of attack (AoA) through its rotation. Consequently, VAWT blades generally use symmetrical aerofoils with a lower lift-to-drag ratio than cambered aerofoils tailored to maximise HAWT rotor performance. Furthermore, the blades of large HAWTs use active blade pitch control to maximise performance for different operating conditions which is mechanically complex to replicate for VAWTs due to the cyclic variation of AoA. Consequently VAWTs generally have a lower aerodynamic efficiency than an equivalent sized HAWT, which increases the CoE.

Tasks and expected milestones/deliverables: This research will consider how VAWT designs might be improved to overcome these limitations, using technologies such as blade cyclic pitch control, variable geometry or active flow control, to propose novel design methodologies that can be exploited by wind turbine manufacturers. This proposed research will develop a thorough understanding of VAWT aerodynamic behaviour and develop a fully coupled aero-elastic model using high fidelity Computational Fluid Dynamic (CFD) as well as vortex or blade element momentum models to explore cyclic load control methodologies.