2.4. Airfoil feature and modification

2.4.1. Geometric features

The FoilGeoFeatures class provides functions to extract geometric features from the airfoil data.

Geometric features:

  • Leading edge radius

  • Volume

  • Thickness line

  • Camber line

  • Curvature

  • Maximum thickness

  • Thickness at 20% chord and 70% chord

  • Maximum camber

  • Average camber

  • Weighted average camber

  • Average camber of front 60% and rear 40%

  • Leading edge slope angle

  • Trailing edge wedge angle

  • Trailing edge slope angle

  • Upper crest point

  • Lower crest point

../../_images/airfoil-geometric-features-tail-0.000.png

Figure 2.4.1 Airfoil geometric features (tail=0.000)

../../_images/airfoil-geometric-features-tail-0.004.png

Figure 2.4.2 Airfoil geometric features (tail=0.004)

2.4.2. Geometric modification

The FoilModification class provides functions to add bumps and incremental curves to airfoil upper and lower surfaces, or add bumps to the airfoil thickness line or camber line. The modified geometry will be reconstructed by the CST method with the specified number of CST parameters.

In Figure 2.4.3, a bump centered at \(x=0.30\) are added to the airfoil upper surface, and a bump centered at \(x=0.85\) are added to the airfoil lower surface. When the airfoil maximum thickness is kept the same, the lower surface is affected by adding the bump to the upper surface.

../../_images/airfoil-modify-bump.png

Figure 2.4.3 Add bumps to the airfoil surfaces (not keep the \(t_\text{max}\))

../../_images/airfoil-modify-bump-keep-tmax.png

Figure 2.4.4 Add bumps to the airfoil surfaces (keep the \(t_\text{max}\))

In Figure 2.4.5, the airfoil camber is increased in a global sense by adding a bump centered at \(x=0.30\). In Figure 2.4.6, the airfoil camber is increased locally in the aft loading region, a bump centered at \(x=0.80\) is added to the airfoil camber line.

../../_images/airfoil-modify-camber-x-0.3.png

Figure 2.4.5 Increase airfoil camber in a global sense (bump center = 0.3)

../../_images/airfoil-modify-camber-x-0.8.png

Figure 2.4.6 Increase airfoil camber in the aft loading region (bump center = 0.8)

2.4.3. Leading edge modification

The FoilModification class provides functions to modify global geometric features of airfoils.

Leading edge radius

In Figure 2.4.7, the airfoil leading edge radius is increased by adding a bump centered at \(x=0.005\) to the airfoil thickness line. Similarly, the radius can be reduced, as shown in Figure 2.4.8.

../../_images/airfoil-modify-rLE-0.016.png

Figure 2.4.7 Increase airfoil leading edge radius

../../_images/airfoil-modify-rLE-0.005.png

Figure 2.4.8 Reduce airfoil leading edge radius

Leading edge slope angle

In Figure 2.4.9, the airfoil leading edge slope angle is increased by adding a bump centered at \(x=0.05\) to the airfoil camber line. The bump width is 0.6 so that the modification is more locally. In Figure 2.4.10, the bump width is increased to 1.0.

../../_images/airfoil-modify-LE-slope-angle-2.5.png

Figure 2.4.9 Increase airfoil leading edge slope angle (bump width = 0.6)

../../_images/airfoil-modify-LE-slope-angle-5.0.png

Figure 2.4.10 Increase airfoil leading edge slope angle (bump width = 1.0)

2.4.4. Trailing edge modification

The FoilModification class provides functions to modify global geometric features of airfoils.

Wedge angle

../../_images/airfoil-modify-TE-wedge-angle-14.7.png

Figure 2.4.11 Increase airfoil trailing edge wedge angle

../../_images/airfoil-modify-TE-wedge-angle-2.6.png

Figure 2.4.12 Reduce airfoil trailing edge wedge angle

Slope angle

../../_images/airfoil-modify-TE-slope-angle-14.1.png

Figure 2.4.13 Increase airfoil trailing edge slope angle

../../_images/airfoil-modify-TE-slope-angle-1.2.png

Figure 2.4.14 Reduce airfoil trailing edge slope angle

2.4.5. Maximum thickness location

The FoilModification class provides functions to modify global geometric features of airfoils.

The maximum location is changed by transforming the x coordinates. The details can be found in CoordinateTransformation.

../../_images/airfoil-modify-x_tmax-0.3.png

Figure 2.4.15 Transform the airfoil maximum thickness location to 30% chord

../../_images/airfoil-modify-x_tmax-0.5.png

Figure 2.4.16 Transform the airfoil maximum thickness location to 50% chord

2.4.6. Thickness at certain locations

The FoilModification class provides functions to modify global geometric features of airfoils.

The thickness is modified by adding bumps to the thickness line.

../../_images/airfoil-modify-t-x0.20.png

Figure 2.4.17 Change the airfoil thickness at x=0.20

../../_images/airfoil-modify-t-x0.70.png

Figure 2.4.18 Change the airfoil thickness at x=0.70

2.4.7. Average camber

The FoilModification class provides functions to modify global geometric features of airfoils.

The camber is modified by adding bumps to the camber line.

../../_images/airfoil-modify-camber-front.png

Figure 2.4.19 Change the airfoil average camber of the front 60%

../../_images/airfoil-modify-camber-rear.png

Figure 2.4.20 Change the airfoil average camber of the rear 40%