Blade surface finish

[zvizdic]

I left my blades rather rough painted . I can see they are underperforming so warmer weather is coming and i am planing on improving them.
I would like to hear any experiences with rough and smooth finish on the blades. I'm pretty sure it makes them stall.  

[SparWeb]

Funny you should ask, considering what I was photographing the morning...  (posted a new thread about it since it looks cool).

Stall isn't the same thing as drag.
Stall happens when the blade (or wing or airfoil of whatever type) has too much angle of attack.  The lift it was developing drops.

Drag happens to everything that passes through the air.  Smooth surfaces do better than rough ones for sure.
In a wind turbine, drag robs some of the power when it is operating... less than you might expect.
By all means, a well polished blade will work better than a rough one.

On the other hand stall is an indication that the generator puts too much load on the blades.  The blades can't get enough lift to crank it over before the angle of attack gets too high.

The signs of blade stall is low RPM, or blades whose RPM doesn't increase in proportion to wind speed.  If you have the data to calculate the TSR, if it's less than 50% of the design TSR then the blades probably are stalled, much less than that and they definitely are.

[imsmooth]

http://www.mindchallenger.com/wind/axial13.html

I used epoxy marine paint and sanded up to 1500 grit paper for a smooth finish.  I then coated with two coats of automotive clear coat.  Smooth like a baby's behind...

[offgridgirl]

Hubby sanded with 100 grit and coated with Linseed oil.  We have more trouble at high speed and furling out of the wind than low speed.

[zvizdic]

I apologize for the wrong term, but you know what I thought.
Winter was on the doorstep, time was limited with other jobs and thus remained incomplete.
With warmer days I plan to do a good surface finish and add a a dip the the front surface.
I hope a dip will provide more lift.

[fabricator]

It's the downwind surface, the side not facing the wind that makes lift on a turbine rotor.

[zvizdic]

OK torque (Terms)are my bad side.
That is why I am millwright and not a teacher.

[Watt]

Funny you should ask, considering what I was photographing the morning...  (posted a new thread about it since it looks cool).

Stall isn't the same thing as drag.
Stall happens when the blade (or wing or airfoil of whatever type) has too much angle of attack.  The lift it was developing drops.

Drag happens to everything that passes through the air.  Smooth surfaces do better than rough ones for sure.
In a wind turbine, drag robs some of the power when it is operating... less than you might expect.
By all means, a well polished blade will work better than a rough one.

On the other hand stall is an indication that the generator puts too much load on the blades.  The blades can't get enough lift to crank it over before the angle of attack gets too high.

The signs of blade stall is low RPM, or blades whose RPM doesn't increase in proportion to wind speed.  If you have the data to calculate the TSR, if it's less than 50% of the design TSR then the blades probably are stalled, much less than that and they definitely are.

I know I'm not referencing a blade but, a golf ball has the dimples for faster, further and less friction flight through the air ( I think ).  Would, if the statement is true, dimples help a blade?  I know I don't see dimples on an airplane wing so......  Anyway, just a wonder?

[jarrod9155]

I used 2 to 3 coats of automotive clear coat and sanded with 320  looks good and performs great .

[SparWeb]

I know I'm not referencing a blade but, a golf ball has the dimples for faster, further and less friction flight through the air ( I think ).  Would, if the statement is true, dimples help a blade?  I know I don't see dimples on an airplane wing so......  Anyway, just a wonder?

They're really different things.  Airplane wings don't have dimple patterns either.
If I tried to go into it I would probably write a lot of stuff that would only expose my ignorance.
I'm happy with the "gut feel" explanation that the dimples keep the boundary layer large, which somehow helps the ball keep turning, which ultimately lets it travel faster, or straighter, or something like that.  I don't play golf, either.   

[WindriderNM]

myth busters did a show putting dimples an a car a few years ago As I recall it decreased the drag.

[GoVertical]

Greetings, shark shin is like sand paper, they say it has less drag in water then a smooth surface. I am not sure if the some thing happens air.

[fabricator]

And Dolphins have a very slippery skin surface and an almost perfect laminar flow.

[zvizdic]

OK
Smooth like a baby's behind will decrease drag and wally to front face for increased torque.
If that thus not give enough torque and speed I am going to machine new blades whit Geo 222 profile .
Chris O mentioned somewhere 10 degrees pitch angle on G12 machine.
2x6 pine for 10' mill should be good .

[ghurd]

I am not a marine biologist who has petted everything in the 7 seas.
I am a tourist interested in local native fauna.  Usually, "it tastes like chicken".  Or shrimp.

Greetings, shark shin is like sand paper, they say it has less drag in water then a smooth surface. I am not sure if the some thing happens air.

Shark skin is scales.  It feels very smooth when rubbing head to tail.  It feels like sand paper when rubbing from tail to head.

And Dolphins have a very slippery skin surface and an almost perfect laminar flow.

Dolphins have skin, like you said, not scales.  To me it feels like "solidified wet oily greasy fat".  It feels like what many people imagine snakes feel like?

Some Whales have tubercles on their fins.  My current understanding is they mostly effect the leading edge of the fin by creating vortices, which makes the remainder of the fin more efficient.


It sound like VERY carefully placed and sized divits may be better than smooth on the leading edge. 
I don't think 'rough' would make any real difference in efficiency.  Whale tubercles look huge to me.  Golf ball dimple/tubercles look tiny.
I can not see it being worth the effort after considering water and air properties of density, viscosity, and moving speed.
G-

[bj]

Back a couple of years ago, there was a bit being done with the leading edge bumps on turbine blades.  If I remember correctly, the initial
numbers looked promising.  Then there was a bunch of negative stuff saying the testing was flawed.  The last I remember was that they had
set up two identical turbines,  withing a mile of each other, but one had the bumps on the leading edges.  The idea was to get long term
testing, and numbers. 
I haven't seen anything since, and the computer with the links is long gone.
I suspect that if there was anything astounding found, it would be seen somewhere, although, maybe they are just being cautious this time.

[bj]

If I did this  right, this is the link to the tubercles on blade leading edges.

http://www.technologyreview.com/Energy/20379/page2/?a=f