Quiz 5

Question 1

What is a fluid?

Answer 1

A fluid is a substance that continually deforms (flows) when a force is applied, no matter how small

Question 2

What does a low Knudsen number mean and how is that used in CFD?

Answer 2

It allows a fluid to be considered a continuum, which in turn allows one to ignore the micro structure of the fluid and represent it using macroscopic properties (density, temperature, pressure etc.). To apply NS-equations this criteria must be fulfilled.

Question 3

What are the three basic conservation laws that can be applied to any physical system?

Answer 3

o Conservation of mass
o Conservation of momentum
o Conservation of energy

Question 4

What is the difference between a Lagrangian frame of reference and a Eulerian frame of reference?

Answer 4

o Lagrangian frame of reference - the position and properties is a function of time
o Eulerian frame of reference - the properties is a function of space and time.

Question 5

Why can’t the Navier-Stokes equations be solved analytically?

Answer 5

o Closure problem, 5 equations but 16 unknowns

Question 6

In slide 36 of Phil’s lectures (5 - Introduction to Fluid Dynamics), what form of the governing equations does FDS use?

Answer 6

Incompressible NSE (density not dependant on pressure, only temperature)

Question 7

What are the typical length scales present in a fire scenario? (xx, some only said meters)

Answer 7

Domain - 10s of meters, fire source - meters, large eddies – 10 cm, small eddies – 1 cm

Question 8

Do we typically resolve the chemical reaction time scales when we use FDS?

Answer 8

No, they are very quick