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JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY
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CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
What make fluid mechanics different
to solid mechanics?
LECTURE CONTENTS
Section 0: Introduction
Section 1: Fluid Properties
Fluids vs. Solids
Viscosity
Newtonian Fluids
Properties of Fluids
Section 2: Statics
Hydrostatic pressure
Manometry/Pressure measurement
Hydrostatic forces on
submerged surfaces
Section 3: Dynamics
The continuity equation.
The Bernoulli Equation.
Application of Bernoulli equation.
The momentum equation.
Application of momentum equation.
Section 4: Real Fluids
Boundary layer.
Laminar flow in pipes.
Section 5: Dimensional Analysis
An Intro to Dimensional analysis
Similarity
xThe nature of a fluid is different to that of a solid
xIn fluids we deal with continuous
streams of fluid.
In solids we only consider individual elements.
In this section we will consider how we
can classify the differences in nature
of fluids and solids.
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CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
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What do we mean by nature of a fluid?
Fluids are clearly different to solids.
But we must be specific.
We need some definable basic
physical difference.
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
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CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
We know that fluids flow under the
action of a force, and the solids don’t but solids do deform.
CIVE1400: Fluid Mechanics
What use can we make of these ideas?
In the analysis of fluids
we often take small volumes (elements)
and examine the forces on these.
So we can say that
xfluids lack the ability of solids to
resist deformation.
Take the rectangular element below.
xfluids change shape as long as a
force acts.
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What forces cause it to deform?
(These definitions include both
gasses and liquids as fluids.)
A
C
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
Section 1: Fluid Properties
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CIVE1400: Fluid Mechanics
B
D
Section 1: Fluid Properties
4

CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
A’
B’
F
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
Fluids in motion
Consider a fluid flowing near a wall.
- in a pipe for example -
F
C
D
Fluid next to the wall will have zero velocity.
Forces acting along edges (faces), such as F,
are know as shearing forces.
The fluid “sticks” to the wall.
From this we arrive at the definition:
Moving away from the wall velocity increases
to a maximum.
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A Fluid is a substance which deforms continuously,
or flows, when subjected to shearing forces.
This has the following implications
for fluids at rest:
v
Plotting the velocity across the section gives
“velocity profile”
If a fluid is at rest there are NO shearing forces acting
on it, and
any force must be acting perpendicular to the fluid
Change in velocity with distance is
“velocity gradient” =
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
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CIVE1400: Fluid Mechanics
du
dy
Section 1: Fluid Properties
6

CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
As fluids are usually near surfaces
there is usually a velocity gradient.
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
What use is this observation?
Under normal conditions one fluid
particle has a velocity different to its
neighbour.
Particles next to each other with different
velocities exert forces on each other
(due to intermolecular action ) ……
It would be useful if we could quantify
this shearing force.
This may give us an understanding of
what parameters govern the forces
different fluid exert on flow.
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i.e. shear forces exist in a fluid moving
close to a wall.
We will examine the force required to
deform an element.
What if not near a wall?
Consider this 3-d rectangular element,
under the action of the force F.
v
No velocity gradient, no shear forces.
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
7
CIVE1400: Fluid Mechanics
Section 1: Fluid Properties
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