08/ Oa

Question 1

What is drag?

Answer 1

Drag is the force which opposes movements

Question 2

Profile drag

Answer 2

Form drag + skin friction cdrag
Skin friction can also be viscous shear drag

Question 3

What . does the boundary layer influence, tell me about the laminar boundary layer.

Answer 3

All effects of skin friction drag will take place within the boundary -
-Few mm deep
Shallow velocity gradient
Low flow speed near surface induces separation

Question 4

Turbulent boundary layer

Answer 4

Few cm deep
Chaotic flow with different directions and speeds
Steeper velocity gradient
Energy exchanged between layers
Greater ke in lower level resists separation

Question 5

Factors determining the transition point

Answer 5

Laminar flow occurs when viscous forces are dominant
Turbulent flow occurs when high inertial forces are dominant.

Question 6

Reynolds number

Answer 6

Describes the value of inertial forces touiscousforces
<500K = - laminar
>10Mi turbulent

Question 7

Effect of surface roughness

Answer 7

= more friction reduces flow energy
Earlier change from laminar in turbulent.
e.g. Dirty or icy wing surface

Question 8

What type of speed and camber will lead a to move turbulent flow

Answer 8

Low speed, high camber
Maximum thinness at 30% chord

Question 9

Separation point

Answer 9

Where the boundary layer separates from the upper surface
Behind this is flow reversal

Question 10

Factors determining the type of boundary layer

Answer 10

Speed of flow
Distance from reading edge
Surface roughness
Position of the point of maximum thickness