Method and system for calculating aerodynamic force of wind turbine airfoil under different turbulence intensities

1 . A method for calculating aerodynamic force of a wind turbine airfoil under different turbulence intensities, comprising:

measuring wind pressure at each pressure measurement point on an airfoil surface of a wind turbine under the different turbulence intensities;

calculating a lift coefficient and a drag coefficient for the airfoil according to the wind pressure at each pressure measurement point on the airfoil surface and thus obtaining lift coefficients and drag coefficients at the different turbulence intensities;

performing function fitting on the lift coefficients and the drag coefficients at the different turbulence intensities, respectively, to obtain a fitted lift coefficient model with an angle of attack as a variable and a fitted drag coefficient model with the angle of attack as a variable at the different turbulence intensities, wherein the performing the function fitting comprises:

performing function fitting on the lift coefficients at the different turbulence intensities to obtain the fitted lift coefficient model f(x) with the angle of attack as the variable at the different turbulence intensities:

f

⁡

(

x

)

=

a

1

⁢

x

4

+

a

2

⁢

x

3

+

a

3

⁢

x

2

+

a

4

⁢

x

+

a

5

,

wherein x denotes the angle of attack, and α 1 , α 2 , α 3 , α 4 and α 5 are a first fitting parameter, a second fitting parameter, a third fitting parameter, a fourth fitting parameter and a fifth fitting parameter of the fitted lift coefficient model, respectively; and

performing function fitting on the drag coefficients at the different turbulence intensities to obtain the fitted drag coefficient model f(x) with the angle of attack as the variable at the different turbulence intensities:

f

′

⁡

(

x

)

=

b

1

⁢

x

9

+

b

2

⁢

x

8

+

b

3

⁢

x

7

+

b

4

⁢

x

6

+

b

5

⁢

x

5

+

b

6

⁢

x

4

+

b

7

⁢

x

3

+

b

8

⁢

x

2

+

b

9

⁢

x

+

b

10

,

wherein b 1 , b 2 , b 3 , b 4 , b 5 , b 6 , b 7 , b 8 , b 9 and b 10 are a first fitting parameter, a second fitting parameter, a third fitting parameter, a fourth fitting parameter, a fifth fitting parameter, a sixth fitting parameter, a seventh fitting parameter, an eighth fitting parameter, a ninth fitting parameter and a tenth fitting parameter of the fitted drag coefficient model, respectively;

calculating a turbulence intensity on the wind turbine to be measured according to a height at which the wind turbine to be measured is located;

obtaining the lift coefficient and the drag coefficient for the airfoil of the wind turbine to be measured according to the turbulence intensity on the wind turbine to be measured by using the fitted lift coefficient model with the angle of attack as the variable and the fitted drag coefficient model with the angle of attack as the variable at the different turbulence intensities; and

adjusting the airfoil of the wind turbine to be measured according to the lift coefficient obtained and the drag coefficient obtained.

2 . The method for calculating aerodynamic force of the wind turbine airfoil under the different turbulence intensities according to claim 1 , wherein calculating the lift coefficient and the drag coefficient for the airfoil according to the wind pressure at each pressure measurement point on the airfoil surface and thus obtaining lift coefficients and drag coefficients at the different turbulence intensities comprises:

calculating a wind pressure coefficient for each pressure measurement point on the airfoil surface according to the wind pressure at each pressure measurement point on the airfoil surface by using an equation

C

pi

=

p

i

-

p

s

p

i

-

p

s

,

 wherein C pi denotes the wind pressure coefficient for an ith pressure measurement point on the airfoil surface, while p i denotes the wind pressure at the ith pressure measurement point on the airfoil surface, p s denotes static pressure, and p t denotes total wind pressure for all pressure measurement points on the airfoil surface;

calculating the lift coefficient C L for the airfoil according to the wind pressure coefficient for each pressure measurement point on the airfoil surface by using an equation

C

L

=

-

∑

1

80

⁢

p

i

⁢

L

i

⁢

sinθ

i

1

2

⁢

ρ

⁢

U

∞

2

⁢

c

=

-

∑

1

80

⁢

Cp

i

⁢

L

i

⁢

sinθ

i

/

c

,

 wherein L i denotes an arc length represented by the ith pressure measurement point, θ i denotes an included angle between a normal direction of the ith pressure measurement point and an inflow direction, C pi denotes the wind pressure coefficient for the ith pressure measurement point on the airfoil surface, c denotes a chord length of the airfoil, ρ denotes air density, and

U

∞

2

 denotes a square of a velocity, and 80 is a total number of the pressure measurement points; and

calculating the drag coefficient C D for the airfoil according to the wind pressure coefficient for each pressure measurement point on the airfoil surface by using an equation

C

D

=

-

∑

1

80

⁢

p

i

⁢

L

i

⁢

cosθ

i

1

2

⁢

ρ

⁢

U

∞

2

⁢

c

=

-

∑

1

80

⁢

Cp

i

⁢

L

i

⁢

cosθ

i

/

c

.

3 . The method for calculating aerodynamic force of the wind turbine airfoil under the different turbulence intensities according to claim 1 , wherein calculating the turbulence intensity on the wind turbine to be measured according to the height at which the wind turbine to be measured is located, comprises:

calculating a turbulence intensity I z (z) on the wind turbine to be measured according to the height at which the wind turbine to be measured is located by using an equation I z (z)=I 10 Ī z (z),

wherein Ī z (z) denotes a turbulence intensity proportionality coefficient,

I

z

_

⁡

(

z

)

=

(

z

10

)

-

α

,

 while z denotes the height at which the wind turbine is located, α denotes a ground roughness exponent, and I 10 denotes a nominal turbulence intensity at a height of 10 m.