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I have recently conducted a small scale wind turbine experiment. The experiment consisted of a small turbine in a wind tunnel. I recorded power output at 5 data points a varying wind speeds from about 2 to 13 mph. I was wondering if someone could help explain some of the results I obtained. See the attached photo for the data.

Two data points seems to defy the laws of physics; the first and the second. Take for example the first point. At a wind speed of 1.997 mph the generator output was 6.174 mW. When I calculated the theoretical maximum in column F, the theoretical maximum was just under 1 mW.

Here is the equation I used for the theoretical power:

P = 0.5*rho*A*V^3*0.593

rho = air density (kg/m^3)
A = Area of sweeping turbine blades (m^2)
V = Velocity (m/s)
(0.593 is the Betz ratio)
The above equation works out to units of Watts. I multiplied by 1000 to obtain mW in the worksheet.

Does anyone have any input as to why the first two data points produce a power output higher than the theoretical maximum?

apuffer

Trying to answer these question you need the experts. Here is a link to a source I subscribe to that can answer almost any questions when it comes to Wind: http://tech.groups.yahoo.com/group/small-wind-home

There is a person named 'Nando' who is your best man to explain this unique observation. This site is a public site that was first started by AWEA.org or the American Wind Energy Association.

Hope this helps

Nflight

Greetings apuffer,

Your situation is an old and well known condition to developers of wind powered water pumps. More than a few companies developed wind power systems using wind tunnels to test systems. You are a victim of what is known as the "side wall effect." Wind tends to see a wind rotor as a disk that is partially solid. This causes wind to build up a high pressure area in front of the rotor and for a percentage - about 50% to go around the rotor and wind power calculations take this into account. The airflow is constrained in a wind tunnel by the "side wall" and forces a higher percentage of wind than normal to go through the wind rotor and hence produce misleading data can send shivers down the spine of inventors and investors.

You cannot get accurate data testing a wind power system in a wind tunnel, unless the wind tunnel is vastly and I mean VASTLY over sized.

Thank you for asking the question. I know of a number of others who just ran off to the market and spent large amounts of OPM announcing great discoveries only to fall flat on their face.

Tom Conlon http://www.ironmanwindmill.com