1. 3 Major Classifications 1. Hydrodynamics: using
math to describe fluid
motion (like physics)
2. Hydraulics: using em-
pirical correlations to
solve engineering prob-
lems
3. Computational Fluid
Dynamics (CFD): using
computers to solve field
eqns (PDE's) modeling
fluid motion
2. Definition of a Fluid a substance that
deforms continuously
when acted on by a
shear stress of any mag-
nitude.
3. Continuum A homogenous and in-
finitely divisible sub-
stance. All fluid charac-
teristics we care about
(e.g. velocity, pressure,
etc.) vary continuously
throughout the field.
4. Properties of fluids Density: mass per unit
volume
- density of liquids varies
little with pressure and
temperature
- density of gases varies
greatly with pressure
and temperature
specific weight: weight
per unit volume
ratio of the density of a
fluid to the density of wa-
ter at 4C
6. Pressure The normal force per unit
area exerted on a plane
surface (real or imagi-
nary) within a fluid
7. "No slip" condition an extremely thin layer
of fluid sticks to all solid
boundaries
8. viscosity A measure of how easily
a fluid flows
A measure of the resis-
tance of a fluid to an ex-
tremely applied shear
9. How does absolute viscosity depend on pres- Absolute viscosity has
sure and temperature? a low dependence on
pressure but a high de-
pendence on tempera-
ture. At higher tempera-
tures, mu of liquids goes
down and mu of gases
goes up. (mu being the
coefficient of viscosity).
10. Bingham Plastic a linear variation of tau
with respect to du/dy af-
ter an initial shear stress
is achieved.
ex: toothpaste, mayo
11. Shear Thickening The harder it is
sheared/strained, the
more viscous it becomes
ex: oobleck
13. Surface Tension Occurs at a liquid-gas
or immiscible liquid-liq-
uid interface. Acts like a
"skin" holding liquid to-
gether.
Owing to unbalanced co-
hesive forces
- molecular forces in in-
terior are equally distrib-
uted
- molecules on surface
are down more strongly
to interior
14. Hydrophobic Water does not stick
to hydrophobic surfaces
and forms spherical
shaped droplets
15. Hydrophilic Water sticks to surface
and spreads out more.
16. Fluid Statics A fluid is considered sta-
tic if all fluid particles are
at rest or have the same
velocity relative to an
internal reference. Fluid
is undergoing rigid body
motion
17. How does pressure vary with direction? It doesn't
18. What does it mean that pressure is independent 1. Pressure is indepen-
of direction and that it varies with depth? dent of container shape
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