Fluid Mechanics Introduction

1. Unit I
INTRODUCTION TO FLUID AND
FLUID MOTION.
15ME303- Fluid Mechanics and Machinery
Lecture 1
Fluid Mechanics , Laws of Fluid Mechanics, Types of fluid

2. General Objective
• Students are able to understand the concept of fluid
mechanics and its laws along with its applications.
Specific Objective
1. Recognise the term Fluid Mechanics and its uses in
real world situations.
2. Classify the five types of fluids with an example.
3. List six Governing Laws of fluid mechanics.

3. INTRODUCTION
Fluid mechanics deals with
liquids and gases in motion or
at rest.
Mechanics: The oldest physical
science that deals with both stationary
and moving bodies under the influence
of forces.
Statics: The branch of mechanics that
deals with bodies at rest.
Dynamics: The branch that deals with
bodies in motion.
Fluid mechanics: 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.
Video-1:

5. What is a Fluid?
Fluid: A substance in the liquid
or gas phase.
A solid can resist an applied
shear stress by deforming.
A fluid deforms continuously
under the influence of a shear
stress, no matter how small.
In solids, stress is proportional
to strain, but in fluids, stress is
proportional to strain rate.
When a constant shear force is
applied, a solid eventually stops
deforming at some fixed strain
angle, whereas a fluid never
stops deforming and
approaches a constant rate of
strain.
Deformation of a rubber block
placed between two parallel plates
under the influence of a shear
force. The shear stress shown is
that on the rubber—an equal but
opposite shear stress acts on the
upper plate.

6. 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.
When the walls are removed or a
liquid container is tilted, a shear
develops as the liquid moves to
re-establish a horizontal free
surface.
The normal stress and shear stress at
the surface of a fluid element. For
fluids at rest, the shear stress is zero
and pressure is the only normal stress.

7. Unlike a liquid, a gas
does not form a
free surface, and it
expands to fill the
entire available
space.
In a liquid, groups of molecules can move relative to each other, but the
volume remains relatively constant because of the strong cohesive
forces between the molecules. As a result, a liquid takes the shape of the
container it is in, and it forms a free surface in a larger container in a
gravitational field.
A gas expands until it encounters the walls of the container and fills the
entire available space. This is because the gas molecules are widely
spaced, and the cohesive forces between them are very small. Unlike
liquids, a gas in an open container cannot form a free surface.

8. The arrangement of atoms in different phases: (a) molecules are at
relatively fixed positions in a solid, (b) groups of molecules move about each
other in the liquid phase, and (c) individual molecules move about at random
in the gas phase.
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.

9. History of Fluid Mechanics
• Archimedes (285 – 212 B.C.) postulated the
parallelogram law for addition of vectors and the laws of
buoyancy and applied them to floating and submerged
objects.
• Leonardo da Vinci (1452 – 1519) stated the equation of
conservation of mass in one‐dimensional steady‐state
flow. He experimented with waves, jets, hydraulic jumps,
eddy formation, etc
• Evangelista Torricelli (1608-1647) who generalized the
analysis of Trajectories of projectiles and the discovery
of barometer is also attributed to him.

10. History of fluid mechanics
• Isaac Newton (1642 – 1727) postulated his laws of
motion and the law of viscosity of linear fluids, now
called Newtonian. The theory first yield the frictionless
assumption which led to several beautiful mathematical
solutions.
• Leonhard Euler (1707 – 1783) developed both the
differential equations of motion and their integral form,
now called Bernoulli equation.
• Navier (1785 – 1836) and Stokes (1819 – 1903) added
newtonian viscous term to the equation of motion, the
fluid motion governing equation, i.e., Navier‐Stokes
equation is named after them

11. History of fluid mechanics
• William Froude (1810 – 1879) and his
son developed laws of model testing
and Lord Rayleigh (1842 – 1919)
proposed dimensional analysis.
• Osborne Reynolds (1842 – 1912)
published the classic pipe experiment and
showed the importance of the
dimensionless Reynolds number, named
after him. 11

12. History of fluid mechanics
• Jean Louis poiseuille(1799-1869) conducted research
on pumping power of heart ,the movement of blood in
veins and capillary vessels and the resistance to flow
through tubes.
• Ludwig Prandtl (1875 – 1953) pointed out that fluid flows
with small viscosity, such as water flows and airflows,
can be divided into a thin viscous layer (or boundary
layer) near solid surfaces and interfaces, patched onto a
nearly inviscid outer layer, where the Euler and Bernoulli
equations apply.
• Theoder von karman (1881-1963) contributed to the
analysis of velocity distribution and resistance to
turbulent flow in pipes as well as long flat surfaces.

13. Fluid as coolants
• Power Plants.(Water flows through Pipe)
• Engines. (Cooling system, Supply Petrol/Diesel from fuel
tank)
• Machining Process.(Coolant used to reduce heat
generation)
• Ordinary coolants like air, water ,Mineral oils and other
organic Liquid have low heat transfer characteristic.
• What’s New ?
Nanoparticles incorporated in the base metal to enhance
the Thermal conductivity and Heat transfer.

14. Aerodynamics:
• Deals with the flow of gases (especially air) over bodies such as
aircraft, rockets, and automobiles at high or low speeds.

15. Meteorology- is the scientific study of the
atmosphere that focuses on weather
processes and forecasting.
Oceanography and Hydrology deals with
Naturally occurring flow.

17. Hydrodynamics: The study of
the motion of fluids that can be
approximated as incompressible
(such as liquids, especially
water, and gases at low
speeds).
Hydraulics: A subcategory of
hydrodynamics, which deals
with liquid flows in pipes and
open channels.
Gas dynamics: Deals with the
flow of fluids that undergo
significant density changes,
such as the flow of gases
through nozzles at high speeds.

18. Types of Fluid

19. NEWTONIAN FLUID
• Where stress is directly proportional to rate of
strain or Fluid with a constant viscosity at a fixed
temperature and pressure.
• These fluids have a linear relationship between
viscosity and shear stress.
• Examples: Water ,thin motor oils, Mineral oil,
Gasoline (Petrol) and Alcohol.

21. NON NEWTONIAN FLUID
• When shear is applied to non-Newtonian fluids, the
viscosity of the fluid changes.
• A non-Newtonian fluid is broadly defined as one for
which the relationship is not a constant. It means that
there is non-linear relationship between shear rate &
shear stress.
• Example :Quicksand ,Corn flour , Starch in water.

22. • Increasing viscosity with an increase in shear
rate characterizes the Dilatant fluid.
• Dilatancy is also referred to as shear
thickening flow behavior.
• Example: Butter, 40% corn Starch solution.
Dilatant Fluid

24. Pseudoplastic Fluid
• Pseudoplastic is the opposite of Dilatant
i.e. the more shear applied, the less
viscous it becomes.
• Pseudoplastic is also referred to as shear
thinning flow behavior.
Examples: Ketchup ,greases

25. Bingham plastic Fluid
• Bingham-plastic: Resist a small shear stress but
flow easily under larger shear stresses.
• Example: tooth-paste, jellies.

26. Thixotropic fluid
• Fluids with thixotropic properties decrease
in viscosity when shear is applied.
• EXAMPLES : Inks, Paints ,Cosmetics,
Glue, Drilling muds.

27. Rheopectic Fluid
• Rheopectic is very similar to Dilatant in that
• when shear is applied, viscosity increases.
• The difference here, is that viscosity increase is
time-dependent.
• Examples : Gypsum paste , Bentonite clay
suspensions

28. RHEOPECTIC VS THIXOTROPIC

29. Graphical Representation

30. Visco elastic Fluid
• Visco-elastic fluids: Some fluids have elastic
properties, which allow them to spring back
when a shear force is released.
• e.g. egg white.

31. Governing laws of fluid Mechanics
• Law of conservation of mass.
• Newtons Law of Viscosity.
• Pascal’s Law.
• Law of conservation of energy
• Newtons Second law.
• Law of conservation of Momentum.