Drag

Question 1

Define (skin) friction drag.

Answer 1

Caused by the attached boundary layer and is dependent on the extent and character of the layer. It is caused by viscosity. Also known as skin friction.

Question 2

Define form drag.

Answer 2

Pressure drag due to flow separation, which occurs due to viscosity.

Question 3

What factors affect pressure drag?

Answer 3

The size of the wake and the position of the separation point.

Question 4

How does the split between pressure drag and frictional drag vary between a cylinder and an aerofoil?

Answer 4

An aerofoil will have less pressure drag due to the smaller wake, and more frictional drag due to larger component of their surfaces in the direction of the flow.

Question 5

Describe the pressure/frictional drag split for a neutral aerofoil at low AoAs.

Answer 5

Skin friction drag&raquo_space; pressure drag.

Question 6

Describe the pressure/frictional drag split for a cambered aerofoil at high AoAs.

Answer 6

Due to early flow separation the pressure drag dominates the friction drag.

Question 7

Describe the difference between laminar and turbulent drag.

Answer 7

For laminar flow, separation occurs earlier, so pressure drag is larger. However, due to the decreased shear stresses in the boundary layer, the frictional drag is smaller.