Wind Turbine Efficiency Discussions

[Christophe]

The last pages concern the robiplan: Science-and-technology / machine rotary-a piston-ring-tri-lobique-t1455-1700.html

This Pascal is a “crazy”, a litmus professor! I have great respect for his mechanical setups and inventive productivity!

[FALCON_12]

Are we diverting the subject?

Pascal Ha Pham has an account here...but he doesn't come here anymore, I don't know why: pascal-ha-pham-u2032/

He's a friend of Remundo...Hey Remundo, could you tell him to come back from time to time?

We were talking about his robiplan in...2008 here: science-and-technology/bi-plane-rotating-wind-turbine-robiplan-t4872.html

ps: please use the Attachments function for your images, it looks cleaner...

You make me think that when I worked in consumer electronics we tried
to invent a kettle that never overflows the milk . A kettle in which you can put
milk without worrying about having to monitor it, a system modulating the heating power
so that its temperature reaches 99 degrees but never exceeds it.

At the time we gave up and several decades later I see that we were
not so stupid: Remundo also seems to have given up on managing, at least the time
let it cool down a little, Doctor Soupolait!

[Remundo]

Are we diverting the subject?

Pascal Ha Pham has an account here...but he doesn't come here anymore, I don't know why: pascal-ha-pham-u2032/

He's a friend of Remundo...Hey Remundo, could you tell him to come back from time to time?

We were talking about his robiplan in...2008 here: science-and-technology/bi-plane-rotating-wind-turbine-robiplan-t4872.html

I am still in contact with Pascal. Imagine that he is still working on wind turbines with aerodynamic drag. But these latest inventions have evolved and are not 100% published. See here however

I had done an aerodynamic study of its ROBIPLAN, and also of a BIROBI version. See here : http://sycomoreen.free.fr/syco_francais ... OREEN.html

[Christophe]

You make me think that when I worked in consumer electronics we tried
to invent a kettle that never overflows the milk . A kettle in which you can put
milk without worrying about having to monitor it, a system modulating the heating power
so that its temperature reaches 99 degrees but never exceeds it.

At the time we gave up and several decades later I see that we were
not so stupid: Remundo also seems to have given up on managing, at least the time
let it cool down a little, Doctor Soupolait!

Uh, he's looking for the fake idiot, right?
I think he's looking for me...

What do you think ?

[Remundo]

don't get upset

[FALCON_12]

don't get upset

Ah unless you started talking about it, I don't see any explanation...

[Remundo]

Just one more remark, then I'll stop here (unless you're looking for me...then I'll explain again! )

It seems to me, I'm not 100% certain, that the Cx, even in a simple form, cannot be calculated by equation...

Well the answer to your question is nuanced depending on the flow regime.

For flows where viscosity is dominant, which are also called STOKES flows at low Reynolds numbers, the coefficient Cx can be calculated by solving the Stokes equation.


For example for the sphere in laminar Stokes flow, Cx = 3 Pi D eta, and this comes from a calculation. There are curiosities about this for other forms




For flows with a higher Reynolds number, the drag force becomes 1/2 ro S Cx v² and there is no expression resulting from a formal calculation.

It was necessary to determine them 1 by 1 in the wind tunnel, in particular thanks to the first industrial wind tunnel in the world at Eiffel, which is still running...that's why French aeronautics was at the forefront at the start of the 1th century!

Yes indeed, and a strange phenomenon appeared: the drag crisis.

Obviously now we can estimate them by numerical calculation and there are certainly approximation equations to determine a Cx of a fairly simple form by mathematical "compilation" of the Cx found empirically... but I'm NOT SURE!

each shape has its own Cx and it is risky to combine precalculated Cxs even if it is tempting, because all parts of a part are interacting as fluid flows around them.

Fluid mechanics is a complex field which requires more than a few simple equations (which only allow us to give orders of magnitude... when they are used well...), which is why calculus was invented. in finished volume and the wind tunnels...

We can do better than find a few orders of magnitude, but it is true that numerical simulation is an asset for preparing a more efficient wind tunnel experiment.

[Christophe]

it is true that digital simulation is an asset for preparing a more efficient wind tunnel experience

Really?

You can't understand it's between us...

[FALCON_12]

it is true that digital simulation is an asset for preparing a more efficient wind tunnel experience

Really?

You can't understand it's between us...

Can you measure the force exerted by the wind on a stationary 3D shape with your software?

[Christophe]

Yes absolutely but it's more free...