AERO40001 - Aerodynamics

Question 1

What are fluid properties

Answer 1

Density and viscosity

Question 2

What are fluid variables

Answer 2

Pressure and velocity.

Question 3

Main difference between a solid and a fluid.

Answer 3

In a solid, the internal stress is proportional to the strain.
In a liquid, the internal stress if proportional to the time rate of deformation.

Question 4

Define the viscosity of a fluid

Answer 4

The ratio of internal stress to the rate of deformation.

Question 5

How does viscosity change with temperature?

Answer 5

For a liquid, mu increases as temperature decreases.

For a gas, mu decreases as temperature decreases.

Question 6

What is the boundary layer

Answer 6

A region in which the viscosity slows the flow.

Question 7

1 knot in km/hr

Answer 7

1.853

Question 8

1 knot in m/s

Answer 8

0.515 m/s

Question 9

What is a chord line on an airfoil?

Answer 9

The straight line that connects the leading edge and the trailing edge.

Question 10

Define the mean line (or the mean camber line)

Answer 10

A line which bisects the upper and lower airfoil.
If you have camber on an airfoil, then you can generate lift even at low incidences.
It increases the CL max.

Question 11

Define inviscid flow (or ideal flow)

Answer 11

In the region outside the boundary layer and the wake, the rates of deformation or the rates of strain are negligible. Viscous stresses here are negligible.
The flow appears to have no viscosity here.

Question 12

Define turbulence

Answer 12

Result of massive amplification of disturbances in the flow in boundary layers and wakes.

Question 13

Define separation

Answer 13

The effects of viscosity slows down the flow so much near a surface that it cannot follow the surface.

Question 14

What happens when stalling occurs?

Answer 14

A large increase in the pressure drag and a loss of lift.

Question 15

Why might 2 bodies be geometrically similar?

Answer 15

If one is a perfect scale model of the other.
Flows and other relevant similarity parameters are the same.
- Streamline patterns will be same.
- Distribution of pressure when expressed as Cp vs. x/c will be same.
- CL, CD and CM will be same.
- The boundary layer thickness as a fraction of c will be same at the corresponding points x/c along the wing surface.

Question 16

What is the principle of conservation of mass

Answer 16

The rate of change (in time) of mass within a control volume plus the net flux of mass out of the control volume is zero.

Question 17

What happens at the stagnation point?

Answer 17

U = 0. 
Cp = 1.

Question 18

What is the no-slip condition

Answer 18

It states that the tangential velocity at a surface has the same velocity as the surface. If the surface is stationary, then the tangential velocity will be 0.

Question 19

What physical property holds between two streamlines?

Answer 19

Note: A streamline within a flow field is always tangential to the velocity vector.
Between two streamlines, the mass or volume flow must be constant as no flow can cross a streamline.

Question 20

Explain why an aerofoil in inviscid flow produces no lift.

Answer 20

In inviscid flow, there is an infinite suction at the trailing edge. Therefore, there is no pressure distribution such that net forces horizontally and vertically are 0. Therefore, producing no lift or drag.

Question 21

Explain the Kutta Condition. How does it give rise to lift?

Answer 21

It states that the flow must leave the trailing edge smoothly. Therefore, the singularity, or the infinite suction at the trailing edge can’t exist. So, there must be uniform flow.
Therefore, there must be circulation around an aerofoil. Removal of the singularity means that lift can be generated.

Question 22

NOTE ABOUT SHEAR STRESS IN A CYLINDRICAL PIPE

Answer 22

IT ACTS AT 2PIR.

AND ITS NEGATIVE - ITS ALWAYS GOING AGAINST THE FLOW!!!