Fundamentals

Question 1

What is a fluid?

Answer 1

A fluid is a substance that deforms continuously under the application of a shear stress.

Question 2

What are special characteristics of a fluid?

Answer 2

• Fluids flow and change shape (solids do not)
• All fluids respond to an applied force or shear stress; they experience a continuing and permanent distortion
• liquids & gases respond differently

Question 3

What are the assumptions used when modelling a fluid as a continuum?

Answer 3

• number of molecules in a given in a volume is large

- the scale of interest isn’t too small

Question 4

What is the condition for treating air as incompressible?

Answer 4

when velocities &laquo_space;speed of sound

Question 5

What are the effects of normal stress on a fluid body?

Answer 5

Normal stresses give rise to forces acting normal to the surface of the fluid particle
(tend to compress/expand the fluid without changing its shape)

Question 6

What are the effects of shear stress on a fluid body?

Answer 6

Shear stresses give rise to forces that shear the particle & deform its shape
(changes shape without changing volume)

Question 7

What types of stresses are felt in stationary and moving fluids?

Answer 7

Stationary fluids only feel normal stresses

Moving stresses, shearing stresses become important, and both normal and shear stress is felt

Question 8

What is viscosity?

and what is it quantified by?

Answer 8

Viscosity is a measure of how much resistance a fluid has to shear

It is quantified by the dynamic viscosity mu (unit Pa s)

Question 9

When are dynamic and kinematic viscosity used respectively?

Answer 9

When calculating forces and dealing with motion respectively

Question 10

Due to continuum modelling, what is the variable wrt which all integral properties of a fluid have to be calculated by?

Answer 10

Volume