CFD - Governing Equations

Question 1

Fluid Particle

Answer 1

An infinitesimal portion of the fluid as a continuum, which is small compared to the characteristic length scale of the system, but large compared to the molecular length scale.

Question 2

Lagrangian Description

Answer 2

Particle approach, Control Mass (mass volume, material surface), Path line

Question 3

Eulerian Description

Answer 3

Field approach, Control Volume, Streamline

Question 4

Substantive Derivative

Answer 4

The instantaneous time rate of change of a property (e.g. density) of the fluid element as it moves along its path line.

Question 5

Conservation of Mass

Answer 5

Mass flow in and out of a fluid element.

Question 6

Conservation of Momentum

Answer 6

The rate of change of momentum equals the sum of forces on the fluid particle (Newton’s Second Law).

Question 7

Conservation of Energy

Answer 7

The rate of change of energy is equal to the sum of the rate of heat added to and the rate of work done on a fluid particle (first law of thermodynamics).