Aerofoils

Question 1

What three factors affect the pressure distribution of an aerofoil?

Answer 1

The thickness distribution, the centreline camber shape and the AoA.

Question 2

What is the mathematical relationship between Cl and AoA?

Answer 2

Cl = 2 * pi * alpha

Question 3

Which region of the camberline has the largest effect of lift?

Answer 3

The TE.

Question 4

Describe briefly the different ways an aerofoil can stall.

Answer 4

1) Flow can gradually separate at the TE.
2) Flow can separate at the LE abruptly.

Question 5

Describe TE separation in detail.

Answer 5

Flow will separate earlier as the BL is stressed more, e.g. if the AoA increases.
The loss of lift is parabolic.

Question 6

Describe LE separation in detail.

Answer 6

It can occur if the LE is too sharp, or if the aerofoil is very thin.

Question 7

What conditions might cause a laminar bubble to occur?

Answer 7

A highly cambered aerofoil, or low camber with high AoA.

Question 8

Describe how laminar bubbles are created.

Answer 8

The laminar BL starts to separate from the aerofoil. As the BL thickness increases, transition occurs. The turbulent BL reattaches creating an enclosed area of recirculating flow.

Question 9

How to delay transition specifically for an aerofoil?

Answer 9

Increase the camber at the LE, creating a more favourable p gradient.

Question 10

What effects does delaying transition have on an aerofoil?

Answer 10

Decreased drag, and CoP will move rearwards.

Question 11

Describe a method of improving pressure rise on an aerofoil.

Answer 11

Changing the Cp vs x/c from concave to convex (Stratford pressure recovery).