Governing Equations

Question 1

Name the four Physical Principals

Answer 1

1. Mass is conserved
2. Energy is conserved
3. Newton’s 2nd law
4. Species concentration is conserved

Question 2

What are the are the corresponding Governing Equations to their Physical Principals?

Answer 2

1. Mass is conserved = Continuity equation
2. Energy is conserved = Energy equation
3. Newton’s 2nd law = Momentum equation
4. Species concentration is conserved = Species concentration equation

Question 3

Describe the philosophy of obtaining Governing Equations

Answer 3

1. Choose physical principal
2. Apply principal to appropriate model of the flow (in this case a 2D CV)
3. Derive mathematical equations for particular principal

Question 4

Describe Eulerian flow

Answer 4

When the model is fixed in space

Question 5

Describe Lagragain flow

Answer 5

When model is free to move with the fluid

Question 6

Describe the convection transport process

Answer 6

This is the flow transport

Question 7

Describe the diffusion transport process

Answer 7

The is the molecular transport

Question 8

What does the rate of change of phi equal?

Answer 8

Net flow by convection + net molecular transport + sources/sinks + effects of CV

Question 9

Describe what is meant as a continuum

Answer 9

Not looking at the substance as individual particles. This way, density, temperature and velocity are functions of position and time.

Question 10

Define the term ‘Non-Newtonian Fluid’

Answer 10

Non-Newtonian fluids do not have a linear stress-strain relationship. Viscosity doesn’t change with rate of flow.
OR shear stress is not proportional to time rate of strain (eg blood, tomato sauce)

Question 11

In terms of a continuum substance, state how fluid properties are defined.

Answer 11

Temperature, viscosity, density etc are all functions of time. Also, they are said to be ‘continuous and differentiable with no discontinuities’.