FLUID MECHANICS
chapter 1
Introduction
1.1 Definition of fluid
1.2 Type of fluid
1.3 Fluid properties
Topic Outcomes
• Describe the basic concepts of fluid
mechanics and recognize the various
types of fluid flow problems encountered
in practice
What is a Fluid
?
• A fluid is a substance in the gaseous or liquid
form
• Distinction between solid and fluid?
– Solid: can resist an applied shear by
deforming. Stress is proportional to strain
– Fluid: deforms continuously under applied
shear. Stress is proportional to strain rate
Solid
F
  
A
Deformation of a rubber block
placed between two parallel
plates under the influence of a
shear force.
What is a fluid ?
Stress: Force per unit area.
Normal stress: The normal
component of a force acting on a
surface per unit area.
Shear stress: The tangential
component of a force acting on a
surface per unit area.
Pressure: The normal stress in a
fluid at rest.
Zero shear stress: A fluid at rest is
at a state of zero shear stress.
What is a fluid ?
• A liquid takes the shape of
the container it is in and
forms a free surface in the
presence of gravity
• A gas expands until it
encounters the walls of the
container and fills the entire
available space. Gases
cannot form a free surface
• Gas and vapor are often
used as synonymous words
Intermolecular bonds are strongest in solids and weakest in gases.
Solid: The molecules in a solid are arranged in a pattern that is repeated
throughout.
Liquid: In liquids, molecules can rotate and translate freely.
Gas: In the gas phase, the molecules are far apart from each other, and
molecular ordering is nonexistent.
solid
liquid
gas
On a microscopic scale, pressure is determined
by the interaction of individual gas molecules.
However, we can measure the pressure on a
macroscopic scale with a pressure gage.
Liquid and Gas
• Although liquids and gasses behave in much the
same way and share many similar characteristics,
they also possess distinct characteristics of their
own. Specifically
• -Liquid
• A liquid is difficult to compress and often regarded
as being incompressible.
• A given mass of liquid occupies a given volume
and will occupy the container it is in and form a
free surface (if the container is of a larger
volume).
Liquid and Gas
• Gas
• A gas has no fixed volume, it changes
volume to expand to fill the containing
vessel. It will completely fill the vessel so
no free surface is formed.
• A gas is easily to compress and usually
treated as such - it changes volume with
pressure.
Application Areas of Fluid Mechanics
Fluid dynamics is used extensively
in the design of artificial hearts.
Shown here is the Penn State
Electric Total Artificial Heart.
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1–2 ■ A BRIEF HISTORY
OF FLUID MECHANICS
Segment of Pergamon pipeline. Each clay
pipe section was 13 to 18 cm in diameter.
A mine hoist powered by
a reversible water wheel.
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Osborne Reynolds’ original apparatus for demonstrating the
onset of turbulence in pipes, being operated by John Lienhard
at the University of Manchester in 1975.
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The Wright brothers take flight at Kitty Hawk.
Old and new wind turbine
technologies north of Woodward,
OK. The modern turbines have 1.6
MW capacities.
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