Chapter 16 – THE SEMINAR IN MILAN
Instituto di energia, Milan, Italy
Page 132- 135
“This evening, I would like to explain to you the innovative concept of mounted, integrated wind turbines, also known as BUWTs. These are designed to be positioned in urban and semi-urban locations, on the roof of stadia such as the one we have here.”
Richards drew the audience’s attention to a representative scale model of a football stadium that was to form the centrepiece of his presentation. Complete with bespoke turbines mounted on the roof, it sat like a white wedding cake on a raised wooden table just to Richards’ left.
“The advantage of a rooftop position such as this,” he said, “is that it can utilise otherwise dormant space to generate renewable energy. Something that is central to my idea is the Coanda Effect, which is named after another genius, the Romanian scientist and pioneer Henri Coanda. This relates to the behaviour of gases and fluids and is the mechanism by which a stream of air sort of sticks itself to a flat roof as it passes over it.
“The Coanda Effect is easy to demonstrate in general terms— and most simply using the example of a stream of water falling vertically from a tap. If you place a convex object, such as the outside of a glass basin or a spoon, adjacent to this stream of water so that it is just in contact with it, the fluid will attach itself to that surface and bend around it for a considerable distance. If you dangle the spoon next to the stream of water in such a way that it is free to move in any direction, you will feel that it is drawn towards the falling water—rather like a magnet. The extent to which the water sticks to the object will depend upon the precise shape of that object.”
From the pinched expressions from one or two members of the audience, Richards detected a slight air of scepticism, and so he hurried on to the paper-lift demonstration, a trick that Father Luigi had taught him after the priest detected a spark of interest in science and technology in the bright teenager.
“A stream of air—or a wind—behaves in exactly the same way as the water, and, although I cannot use water to demonstrate this for fear of flooding this beautiful auditorium”—he paused in response to the faint murmur of laughter—“I can demonstrate the Coanda Effect on air. In fact, this is something that even a child can do.”
Richards took out a curved piece of paper from under the lectern and placed it on the table. He blew gently across the paper, at right-angles to the axis of the curve, and sure enough, the paper obediently rose.
“This is a principle used in flight aerodynamics,” continued Richards, “with a stream of air bending itself around the convex curve of an aeroplane wing, to provide the aeroplane with lift. What is remarkable about the Coanda Effect is its strength, as it can pull a stream of water for a considerable distance around a curved object and, of course, contributes substantially to lifting heavy aeroplanes into the air.”
The engineer again turned towards the stadium model on the table.1 3 4
“In the case of our football stadium, we will look to shape the stadium roof in order to maximise the advantages of the Coanda Effect. The structure will be designed to actually accelerate the laminar flow of the passing air mass, concentrating the wind in the places where the turbines will be positioned.
“Further gains in energy yield can be achieved through the positioning of the turbines, and also through clever turbine design as demonstrated in research carried out in 2002 by my colleague Professor Stankovic.”
Richards turned, extending his arm to introduce Professor Sinisa Stankovic, who was seated behind him and to his right. “Professor Stankovic proved that a structure located in a typical urban setting, with a built-in horizontal-axis wind turbine, can provide an annual energy yield that is 25 percent more than that of a large, free-standing propeller such as we are accustomed to seeing throughout the world.”
“Yes, an increase of at least 25 percent,” added Stankovic, a tanned, middle-aged Serb with grey, slightly unruly curly hair.
“Turbines having a free-standing position on a roof,” continued Richards, gesturing towards the model of the football stadium in front of him, “will further improve performance, in comparison with turbines that are mounted in a duct within a building.”
“But that doesn’t make sense!” came a voice from the audience. “Surely, the optimum position for a wind turbine would be in the middle of the sea, or a flat plain, where the wind can pass through uninterrupted, with no friction to slow it.”
All heads turned, searching for the source of scepticism.
Standing was a girl in her early twenties with a short, pixie-like hairstyle and rather masculine black-rimmed glasses. She was near the entrance to the auditorium. Richards resented interruptions from the audience, but on this occasion, he welcomed the intervention—having anticipated this very assertion.
“Thank you for broaching that,” he said to the young woman. “The Coanda Effect does, certainly on its face, appear to be counterintuitive. But it is actually not the case. In any moving air mass, there will be natural turbulence and movement so that winds will blow past a given point in several directions. Even a
turbine that is designed to move in order to face the prevailing wind direction will only be able to adapt to a certain extent. Far greater efficiency can be achieved by designing the curvature of urban structures so that they direct and channel airflows to enhance wind speeds where the turbines are located.”
The young woman sank back in her seat.
David Carter, a member of the expert panel who had published extensively in the Journal of Wind Engineering and Industrial Aerodynamics, was anxious to make his mark on the discussion, and saw the interruption from the floor as an opportunity. He was keen to prevent Richards from disseminating the fruits of his life’s work as his own.
“I should emphasise, at this point,” Carter began, tapping the end of a sturdy silver pen on the panellists table, “that large, flat rooves such as those found on most modern sports stadia are ideal for this purpose, as they tend to be of low pitch and provide an extensive area of attached flow, with low correlations between the pressure fluctuations acting on different parts.”