Wing and blade aerodynaimc center

[mezah]

Hello everyone,
Now i am trying to model wind turbine blade using solidworks.

I have the airfoil coordinates at each section of the blade, but the coordinates are distance per chord (x/c,y/c) so i have to scale it using the calculated chord.
When i scale it with respect to the origin - which is at the leading edge - the position of the aerodynamic center for each section is changed with respect to others.
Is the aerodynamic center should be along the same line??
Is this correct or should i do it another way?
Thanks in advance.

 

[Sparweb]

If you picture a wing with compound dihedral, or a gull wing, or a rectangular wing with a wide body fairing strake, you can tell that there is no "correct" aerodynamic center line. If the line drawn through the AC along the wing/blade plan shape is not straight, then it's not straight. If it's easiest for the construction of the turbine blade to have a straight leading edge, then that's what you have constrained yourself to.
Try to remember, though, that the wind turbine blade will be rotating at many many RPM, (depending on its size). If the center of mass of each cross-section meanders like the aerodynamic center line, then it will not be well aligned radially with the axis of rotation either. An induced lead/lag load will be present, which may be insignificant, or cause problems, depending on the size of the turbine and the materials you use.

STF

 

[rb1957]

why would you think the co-ords of the section are based about the ac of the section ?

the chords are non-dimensional (x/c, y/c), the datum for the axes is (0,0).

why do you care particularly about the ac ? (it is "only" the point where Cm is zero)

 

[mezah]

As you can see in the figure below there is a point point where the lift and drag act and the angle is measured ( specially twist angle) it is mentioned before - in the book 'wind energy explained' - that the point is c/4
Taking in consideration that it is only one section and we must have N number of sections, so the other sections should have the same reference point for consistency.

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i tried to draw the blade using each AC of the airfoil at each section (c/4) and it looks like this

The project i used as a guide looks like this

 

[mezah]

i reversed the twist angles from root to tip instead from tip to root and it looks like this

But it still different from the original one and i don't have another reference to compare with

 

[rb1957]

ok, we started talking about how to plot airfoil profile. presumably you've got airfoil co-ordinaes from NACA (in terms of x/c and y/c).

the aerodynamic centre moves as the conditions (certainly AoA, maybe airspeed) change ... it is he point abot which aerodynamic moments are zero, lok at the plot of Cm, it isn't constant.

the 1/4 chord point might be a logical point to overplot airfoils (sections along your blade) ... it is the reference point for aerodynamic coefficients.

the axis (CL) of the blade mounting would obviously be releent to your application ... maybe a better choice.

it's simple enough to transform the co-ordinates of your airfoil to move the origin to another point, yes?

 

[rb1957]

looking at your last two pictures, it strikes me that the upper picture (in blue) may have some fwd sweep. you created a datum between your sections (using the c/4 point). what if you drag the tip point fwd (and drag the other sections proportionally) ?