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As to your assumptions:
Both the source (fan) and the generator have fixed bladed rotors (fan blade
styles). The load of the generator is fixed (100 ohms) and the output is
fed to a voltage/current sensor and then to a program which calculates and
displays the average power versus time. Once the orientations of fan and
generator are optimized, that power is fairly constant. There is a separate
device (rotational motion sensor) that is used to measure wind speed and we
were careful to keep the distances and orientations as constant as possible.
I did not expect the generator power to wind speed to be cubic but was
somewhat surprised when I found it (admittedly one time through--will redo
the experiment this weekend) to be linear (including 0,0). My 'gut' was to
expect something more quadratic (and indeed I've analyzed some data from a
2MW Illinois generator that fits nicely with a v^2 dependency), but realized
we had a lot of transfers going on--ignored the electrical to fan, but wind
to blade and blade rotation to generator--and also had a fairly narrow range
of velocities (.35-.55 m/s). With John's more complete description it is
clear that we have a very complex system. [Just last weekend drove by a new
wind farm going up in Western Indiana with one of the towers very near the
highway. I did note the twist in the blades and a bend at the end--sort of
like a 747 wing. None of those turbines were yet running--near (and I mean
NEAR) the town of Earl Park, Indiana.]
Rick
----- Original Message -----
From: "Brian Whatcott" <betwys1@sbcglobal.net>
>
> This is a scientific observation, and I would like to understand it
> correctly.
> Rick correctly relates wind speed and the available wind power as a cubic,
> or perhaps even better, the difference of two cubics.
>
> In his model environment, he has a wind source provided by a three speed
> fan. One can suppose he measures the electrical power input to the fan
> and also its output wind speed.
> He may possibly see a cubic relation between electrical power input and
> wind speed output on a three point graph, but probably not, because the
> fan is (I imagine) a fixed blade arrangement. And he may be directing
> the airflow into a generator fitted with fixed blades.
> He may then be measuring the generator output voltage, and may possibly
> be providing the generator with a variable load, which he can vary so as
> to maximize the electrical power generated at given airspeeds?
> I apologize for the number of assumptions I am putting into action here
> - I have no insights into Pasco's recommended protocol as you may have
> guessed.
>
> It seems to me better to proceed from this example experiment,
> and generalize from its data where possible.
>
> Just reading this description of Rick's experimental arrangement
> (in my imagined form at least) may already be allowing you to think,
> "Did I really expect to deploy two energy conversions both nominally
> involving cubics, but with numerous sources of speed sensitive
> inefficiencies, and expect to see a neat cubic curve emerge?"
>
> The same sort of considerations may also be applied to the
> slide 11 curves - though one assumes that the windmill blades are
> provided with variable pitch arranged for constant speed given
> sufficient wind.
>
>
>
> Brian Whatcott Altus OK Eureka!
>
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