CHAPTER 1
INTRODUCTION

1.
2.
3.
At the end of this chapter, you should be able
to:
Understand the basic concepts of fluid
mechanics and recognize the various type of
fluid flow problems encountered in practice.
Model engineering problems and solve them
in a systematic manner.
Have a working knowledge of accuracy,
precision, and significant digits, and
recognize the importance of dimensional
homogeneity in engineering calculations

The science that deals with the behavior of
fluids at rest (fluid statics) or in motion (fluid
dynamics), and the interaction of fluids with
solids or other fluids at the boundaries.
It is divided into several categories:
 Examples: hydrodynamics, hydraulics, Gas
dynamics, aerodynamics etc.




A substance in the liquid or gas phase is
referred as FLUID
In fluids, stress is proportional to strain rate.
Stress=force per unit area.
Normal to
surface
Normal stress, σ = Fn/dA
(in fluid at rest, it is called
pressure)
Fn
F
Shear stress, τ = Ft/dA
(for fluid at rest=0)
dA
Ft
Force acting
on area dA
Tangent to
surface
Examples:
 Natural flows & weather
 Aircraft & spacecraft
 Boats
 Human body
 Piping & plumbing systems
 Wind turbines
 and many more…..
Tornadoes
Thunderstorm
Global Climate
Hurricanes
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Aircraft
High-speed rail
Surface ships
Submarines
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Air pollution
River hydraulics
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Blood pump
Ventricular assist device
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Water sports
Auto racing
Cycling
Offshore racing
Surfing
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Uniform approach
velocity, V
Relative velocities
of fluid layers
Zero velocity at
the surface
Plate


A fluid in motion comes to a complete stop at the
surface and assumes a zero velocity relatives to the
surface.
Fluid in direct contact with solid “sticks” to the
surface due to viscous effect, and there is no slip.

Viscous vs inviscid regions of flow
Viscosity -a measure of internal stickiness of fluid
Viscous flow region–significant frictional effect
Inviscid flow region – negligible viscous forces
B.
Internal vs external flow
C.
Compressible vs incompressible
A.




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Incompressible flow – almost constant density
throughout
fluid
Compressible flow gas
Question:Can gas flow be treated as incompressible flow?
Answer: depends on the Mach number (Ma = V/c ); usually when
Ma<0.3
D.
Laminar vs turbulent flow

Determined by Reynolds number, Re
Re < 2000 (laminar); Re > 6000 (turbulent); between
laminar and turbulent is transitional
E.
Natural (or unforced) vs forced flow
F.
Steady vs unsteady flow



Steady = no change at a point of time
Transient = typically used for developing flows,( e.g.
pressure build up inside rocket engine, until it
operates steadily)
Good luck!
1)
2)
3)
4)
What is fluid?
Stress is force per unit area. Name 2 types of
stress in fluid and their equations.
Give 3 examples of application areas of fluid
mechanics.
Please explain about the “no-slip condition”.
You have 10 minutes. TQ!