Harnessing Wind Energy Twice per Revolution
Vertical axis wind turbines (VAWTs) are gaining attention as an alternative to traditional horizontal axis designs because of their ability to capture wind from all directions and reduced visual impact. However, existing VAWT configurations often suffer from performance and structural limitations, hindering their widespread use. This study analyses state-of-the-art VAWT technologies and proposes an innovative framework to address these issues and improve performance. The design integrates advanced aerodynamics, robust structural support, efficient drive mechanisms, and electromagnetic stabilisation to optimise energy conversion and versatility. Key features, such as variable blade positioning and adaptive aerodynamic profiles, enhance energy extraction, grid integration, and resilience. This research demonstrates the potential of integrated VAWT technologies to overcome challenges and enable sustainable energy generation, showcased by four distinct VAWT designs, each with unique characteristics.
By Professor Friedrich Björn Grimm, Founder, RES Institute, Germany
Wind energy is a key pillar of renewable power, addressing climate change and fossil fuel depletion. While horizontal axis wind turbines dominate the sector, vertical axis wind turbines (VAWTs) offer advantages such as omnidirectional wind capture, simpler installation, and lower noise, making them ideal for urban and onshore applications. Despite these benefits, VAWTs face aerodynamic inefficiencies, structural limitations, and reliability concerns.
Orbital Dynamics of the Variable Asymmetrical Airfoil
The 12 orbital positions of the variable asymmetrical airfoil along its circular trajectory illustrate its aerodynamic behaviour throughout the rotation cycle. In relation to the flow direction, the suction side of the airfoil aligns inward during the windward phase and outward during the leeward phase. This dynamic adjustment enables the airfoil, designed as a Clark YM-15 profile in the described turbine, to generate a tangential driving force in the direction of rotation.
At specific turning positions, the suction side of the airfoil transitions between inward and outward orientations, passing through a symmetrical profile in the intermediate phases. The interaction between flow velocity and rotational velocity generates a lift force inclined in the direction of rotation, which is significantly greater for the asymmetrical airfoil compared with a symmetrical counterpart. This optimised aerodynamic response enhances the efficiency of the rotor blade turbine, making it more effective than conventional Darrieus rotors.
Aerodynamic System Design
The proposed wind turbine features a multi-part rotor blade with a variable airfoil profile to maximise energy capture across diverse wind conditions. Comprising three adjustable segments with rigid wing sections, the blade utilises hinges that enable the front and rear segments to pivot, transitioning between symmetrical and asymmetrical profiles. This alignment optimises aerodynamic performance and stabilises rotor speed, even in turbulence. Given the lower speed number of VAWTs, throttling is mainly required at high wind speeds, reducing frequent adjustments and enhancing efficiency. Overlapping joints with hairline gaps minimise flow disruption, while strategic articulation allows seamless adaptation to varying wind speeds and directions. These innovations improve VAWT efficiency, ensuring operation from light breezes to storms. Additionally, adjustable wing blade mechanisms enhance lift generation and reduce stress during extreme weather, increasing stability and reliability.
RES GigaTube 101MW 680m 4B
This elegant turbine features four rotor blades designed with a hyperbolic curvature. Its rotor diameter is wider at the top than at the bottom, maintaining a constant lambda value and ensuring higher in-flow speed at the top compared with the lower section. Elevated well above sea level, the turbine reaches an impressive height and is designed for optimal energy generation at varying wind speeds. All shown VAWTs are designed with a lightweight steel construction and could be even lighter if built with composite materials. With its lightweight structure and exceptional power-to-weight ratio, this VAWT presents a compelling challenge to conventional horizontal axis turbines, offering undeniable performance advantages.
Support System Configurations
The turbine’s support structure features a central mast and a cable net system that stabilises variable rotor blades with pivoting leading and trailing edges. These blades, divided into windward and leeward halves, adjust dynamically via pneumatic or electric actuation. Sensor control ensures optimal orientation to prevailing wind conditions, with the suction side facing inward in windward rotation and outward in leeward rotation. At high lambda values, centrifugal forces surpass lift, mitigated by the concave surface of the hyperbolic prestressed cable net. Spoked wheels within the rotor transfer loads, reducing lateral mast forces and enhancing efficiency.
Two distinct support configurations further optimise performance. The first, a self-supporting lattice shell, integrates interconnected support profiles and tension cables for exceptional stability, accommodating three-part rotor blades with variable airfoil profiles. The second, a guyed cable structure suspended from the central mast, provides a flexible, scalable design with optimal load distribution and dynamic stabilisation, enabling efficient operation at extreme heights. These structural innovations ensure resilience under diverse environmental conditions.
RES GigaTube 51MW 560m 6B
These giant VAWTs feature a hyperboloid structure with a wide rotor diameter at the top that narrows towards the bottom, optimising energy capture. Equipped with six variable pitch blades, they efficiently generate power across a range of wind speeds. The innovative GigaTube design utilises variable asymmetrical profiles to enhance lift, improving performance compared with traditional Darrieus rotors. Its robust structural design ensures all load-bearing elements handle either tensile or compressive forces, maintaining stability even at high rotational speeds. Radial spokes within the cavity between the mast and rotor divide it into shorter sections, while aerodynamic connections between the leeward and windward blades further enhance efficiency. At higher wind speeds, centrifugal forces surpass the lift created by asymmetrical profiles, making this turbine an advanced and cost-effective solution for wind energy production.
RES GigaTube 5MW 220m 6B
The RES GigaTube redefines turbine design, demonstrating clear advantages over conventional models. With a wide in-flow area and a tapered hyperboloid structure, it optimises wind capture. At moderate wind speeds, its six variable pitch blades generate significantly more power than the Enercon E-126, while maintaining a much higher power-to-weight ratio. The GigaTube’s variable asymmetrical profiles enhance lift, outperforming conventional Darrieus rotors. Structurally, all load-bearing elements handle either tensile or compressive forces, ensuring stability even at high speeds. Radial spokes within the cavity divide it into shorter sections, and aerodynamic connections between leeward and windward blades further improve efficiency. At higher wind speeds, centrifugal forces dominate over lift, allowing a more cost-effective construction.
RES GigaTube 10kW 10m 4B
This VAWT features four rotor blades that rotate around a central vertical axis. These blades are interconnected by two annular cross-members and supported by radial cross-members, which link them to a coaxially mounted motor generator at the top of the mast. Each rotor blade consists of a front, middle and rear segment, with the middle segment serving as a structural beam that provides rigidity against bending, shear and torsion, forming a stable rotor module.
The rotor blades are divided into multiple longitudinal sections, creating a continuous blade chain. Each section incorporates actuators that allow adaptive adjustments based on aerodynamic conditions. During rotation, the suction sides of the blades transition from the inner side in the windward phase to the outer side in the leeward phase, with their orientation dynamically adjusted along the flow direction. This adaptive movement ensures efficient energy capture and optimal aerodynamic performance.
Table 1. Technical data of the turbines
Conclusion
The proposed wind turbine design represents a paradigm shift in renewable energy technology, leveraging innovative aerodynamic concepts, advanced support systems, and sophisticated control mechanisms to maximise energy capture efficiency and operational reliability. By integrating cutting-edge technologies across multiple disciplines, the design offers a scalable and sustainable solution for wind power generation, capable of operating efficiently across a wide range of wind conditions. With its dynamic stabilisation system, responsive blade adjustment mechanisms, and robust structural framework, the proposed wind turbine design holds immense potential to revolutionise the renewable energy landscape, paving the way for a more sustainable and resilient future. Continued research and development is necessary for the wind turbine to go into production. This will be crucial for addressing any remaining challenges, optimising performance, and ensuring the reliability of the technology.
Biography of the Author
Professor Friedrich Grimm, CE, studied architecture at the University of Stuttgart and the Illinois Institute of Technology. In this field he is an honorary professor at the University of Stuttgart. Moreover, he is the founder of the RES Institute and an innovator in renewable energy. His recent work includes inventions in quantum mechanics for fusion reactors.
