Accuracy matters in aerodynamic design. When we are developing Rotor Sails, wind tunnel testing remains one of the most valuable ways to measure performance, validate our models and ensure aerodynamic predictions are backed up by physical data prior to full-scale testing on our land-based test site.
Used alongside Computational Fluid Dynamics (CFD) and other numerical methods, wind tunnel testing helps us build a more complete picture of how a Rotor Sail will perform. It allows us to measure aerodynamic forces and flow behaviour in controlled conditions, giving us the data we need to refine aerodynamic designs, strengthen performance predictions and support the next stage of development.
Anemoi recently undertook a wind tunnel testing campaign at the University of Southampton to collect data for various aerodynamic enhancements which we are developing to maximise fuel savings. This was accompanied by a series of CFD investigations, both of which have been primarily funded by the UK government through our Clean Maritime Demonstration Competition Round 6 project.
[Image Caption: Wind Tunnel Testing at the University of Southampton]
Strengthening our aerodynamic understanding
CFD has transformed aerodynamic design, giving us a powerful way to simulate Rotor Sail performance across a wide range of wind speeds, wind angles and operating conditions. It helps us understand how airflow interacts with a rotating cylinder and how thrust is generated. CFD is conducted for a Rotor Sail in isolation and for installations of Rotor Sails on a vessel to understand the aerodynamic interaction effects.
Wind tunnel testing adds another important layer to this work by giving us direct physical measurement of aerodynamic forces. Reduced‑scale wind tunnel tests, especially when combined with CFD, provide solid confidence in the simulations and help show whether new designs are ready for full‑scale prototyping. While there are limitations, such as lower Reynolds numbers and some boundary effects, the combined results of wind tunnel testing with CFD offer strong, reliable insights.
This matters particularly for Rotor Sails because their performance depends on the Magnus Effect, the phenomenon that produces thrust when airflow passes across a spinning surface. Testing allows us to see how that effect behaves in controlled conditions and measure how variables such as wind angle, wind speed and Rotor speed influence aerodynamic forces and end-plate effects.
These measurements help us make sure the aerodynamic behaviour is properly understood and accurately represented within our design models.
We have been using wind tunnel testing in Anemoi’s Rotor Sail development for years. Before our initial Rotor design, we carried out testing at the Auckland wind tunnel in 2008, and we used the results to help inform key elements of that early design before moving towards full scale prototyping at our full-scale Rotor Sail test facility.
[Image Caption: Testing at the Auckland wind tunnel in 2008]
Supporting design optimisation
Wind tunnel testing gives us a practical way to see how design changes affect Rotor Sail performance.
By testing scaled models in controlled conditions, we can evaluate quickly how variations in height, diameter, top disc configuration and operating speeds influence aerodynamic efficiency. This means different configurations can be assessed systematically and compared on a like-for-like basis in a fast and cost-effective manner before trialling new designs at full scale. Atmospheric flow features such as wind shear and turbulence can also be simulated.
The insights from these tests directly support ongoing design refinement. They help us identify the configurations that deliver the strongest aerodynamic performance while still being suitable for practical vessel integration.
The results also feed directly into our day-to-day engineering work. We use wind tunnel data to inform new aerodynamic designs and support performance predictions for those designs. We make these performance predictions by taking the lift and drag coefficients from the wind tunnel model, CFD and full-scale tests and using them to model vessel performance through our Fuel Saving Assessment (FSA) method.
Providing confidence for shipowners considering wind propulsion
For shipowners and operators assessing wind propulsion technologies, reliable performance data is a key part of the picture.
Investment decisions depend on credible estimates of fuel savings, emissions reductions and overall return on investment. Wind tunnel testing helps strengthen these projections by providing proven aerodynamic data that supports the performance modelling behind them.
In practice, this means we are not relying on simulation alone. We are combining advanced numerical analysis with physical testing to build a clearer and more robust view of how our Rotor Sail systems behave under a range of wind conditions.
As interest in wind propulsion continues to grow across the industry, this level of validation becomes increasingly important. Shipowners are looking not just at the technology itself, but at the quality of the engineering behind it, and physical testing plays an important role in giving them greater clarity. We have also been collecting full scale Rotor Sail data at our land-based test facility since 2013, providing long-term, real-world measurements to inform our designs.
This Wind Tunnel testing project was funded by UK Government through the UK Shipping Office for Reducing Emissions (UK SHORE) programme in the Department for Transport. UK SHORE has allocated over £230m since 2022 to develop the technologies necessary to decarbonise the UK maritime sector and capture the economic growth opportunity of the transition. Innovate UK, part of UK Research and Innovation, is the main delivery partner for UK SHORE interventions.
