What is an aerofoil and how does it work?

The scientific theory behind wings and diffusers can be observed all around the world. These principles allow a 560 tonne Airbus A380 to defy gravity and a Formula 1 vehicle to travel at 200 kph around tight corners.

An aerofoil is a 2-dimensional shape specifically designed to interact with air to produce lift – as shown below with some common aerofoil terminology. An aeroplane’s wing can be thought of as an aerofoil ‘extruded’ to form a 3-dimensional shape.

Figure 1 - https://en.wikipedia.org/wiki/Lift_(force)

There are several incorrect theories that try to explain how an aerofoil generates lift. A particularly common theory is called Equal Transit Time. This theory is essentially a misinterpretation of Bernoulli’s principle, as it assumes that fluid particles that ‘divide’ at the leading edge of an aerofoil must ‘re-join’ at the trailing edge. This does not happen and has been proven untrue through careful experimentation (as can be seen in this video: Airflow across a wing - YouTube).

A (very) simplified way to explain the lift force generated by an aerofoil is through Newton’s laws of motion.

1. Newton’s first law: An object will remain in uniform motion in a straight line unless a net force acts upon it. The air will continue travelling in a straight line until a force is applied to it by the aerofoil.
2. Newton’s second law: Force is equal to the mass times the acceleration of an object. The force that the aerofoil imparts on the air is equal to the mass times the net acceleration of the body of air affected. This body of air can be very large, often extending for many metres above and below the aerofoil.
3. Newton’s third law: Every action has an equal and opposite reaction. The force imparted on the air by the aerofoil is in turn imparted on the aerofoil by the air.

Figure 2 - https://en.wikipedia.org/wiki/Lift_(force)

This explanation really only tells part of the story of how lift is produced (how does the aerofoil impart a force on the airflow at great distances from the aerofoil? Why does the air flowing over the top of an aerofoil go much faster than the airflow going under?) but this will suffice for our discussion in this article.

It’s important to note that the direction of lift is not determined by gravity (this is why planes can fly upside down). As a result, the benefits of lift can be applied to many use cases. For example, Formula 1 cars - where the direction of lift is ‘flipped’ (often called down-force) which helps the car ‘stick’ to the track even at extreme speeds.

Wind turbines and diffusers. What are the benefits?

In the case of small wind turbines, the addition of a circular aerofoil (diffuser – think of an aeroplane wing wrapped around to form a ring) can lead to incredible efficiency gains along with a string of other benefits. The lift produced by the diffuser is directed to the centre of the ring and draws a higher volume of airflow through the turbine blades compared to a standard open-bladed wind turbine. It is this increase in airflow that allows the blades to capture more of the wind’s energy.

Improved efficiency. A diffuser maximises the natural wind resource to unlock efficiency gains. Our Hyland 920 wind turbine has an operating efficiency of 42% which is a major improvement compared to existing small wind turbines on the market and is approaching efficiency’s seen in the very large turbines you would see in wind farms.  

Increased safety. In the unlikely event of a catastrophic blade failure, all turbine components and damage will be contained by the diffuser shroud. This has been verified by experimental destructive testing.

Minimal wildlife interaction. Studies have shown that cats, buildings, and vehicles pose far more danger to wildlife than wind turbines. Although rare, animal interactions with wind turbines do occur. The addition of our diffuser helps to prevent these animal interactions, as visibility of the turbine is increased and the blade tips are no longer exposed.

Reduced noise. The addition of an aerodynamic diffuser has been shown to reduce noise output via two main methods; mitigating the creation of noisy blade tip vortices by the physical presence of the diffuser, and damping the transmission of any generated noise as the diffuser effectively acts like a muffler.

Final words.

It’s important to note that it takes years of research and development to design a system where the blades and diffuser work in harmony to improve each other. It is not as simple as putting a circular piece of plastic around the blades.

The Diffuse Energy team have invested more than 4 years of product research and development, including extensive computational simulations, wind tunnel testing, and field testing. Our technology was invented at the University of Newcastle, Australia - and leverages over 20 years of international peer-reviewed small wind turbine research.

If you would like more information on our Hyland 920 wind turbine, please email us at sales@diffuse-energy.com.