2. Fluid Mechanics I – ME362*
Arab Academy for Science, Technology
and Maritime Transportation
Dr. Ahmed Khalifa Mehanna
Associate Professor
a.khalifa@aast.edu
ahmed_marines@yahoo.com
Room No: 223
Course Assistant Lecturer:
Eng. Omar Mostafa
3. Course Objective...
Concepts and Theories of Mathematics and Sciences;
Methodologies of Solving Engineering Problems;
Fundamentals of Fluid processes
Evaluate the Power Losses in the Fluid Transmission Lines and Networks
You will learn about:
Fundamental knowledge of incompressible flow, and easily understanding the
basic principle of hydrostatics and hydrodynamics.
This course will help you to:
Apply and integrate knowledge, understanding and skills of different subjects
to solve real problems in industries.
Textbook
Munson, Young and Okiishi “Fundamentals of Fluid Mechanics”,7th Edition (5 April 2012).
6. Mechanics: The oldest physical science that deals with both
stationary and moving bodies under the influence of forces.
Statics: Branch of mechanics that deals with bodies at rest and
forces in equilibrium.
Dynamics: Branch of mechanics that deals with the motion of
bodies under the action of forces.
Fluid mechanics: The science that deals with the behavior of
fluids either at rest (fluid statics) or in motion (fluid dynamics),
and the interaction of fluids with solids or other fluids at the
boundaries.
Definitions
7. Statics Dynamics
Rigid Bodies
(Things that do not change shape)
Deformable Bodies
(Things that do change shape)
Incompressible Compressible
Fluids
Mechanics
Branch of Mechanics
8. Hydrodynamics: The study of the motion of fluids that can be
approximated as incompressible (such as liquids, especially water)
and the forces acting on solid bodies immersed in them.
(Hydrodynamics also called Marine Hydrodynamics)
Hydraulics: A subcategory of hydrodynamics, which deals with
liquid flows in pipes and open channels.
Gas dynamics: Deals with the flows that having significant changes
in fluid density, such as the flow of gases through nozzles at high
speeds.
Aerodynamics: Deals with the flow of gases, (especially air when it
interacts with a solid object), over bodies such as aircraft, rockets,
and automobiles at high or low speeds.
Meteorology, oceanography, and hydrology: Deal with naturally
occurring flows.
Definitions Cont’.
9. Both gases and liquids are classified as fluids:
Number of fluids engineering applications is enormous:
breathing, blood flow, swimming, pumps, fans, turbines,
airplanes, ships, rivers, windmills, pipes, icebergs, missiles
(rockets), engines, filters, jets, and sprinklers, …….etc.
When you think about fluids engineering applications, almost
everything on this planet either is a fluid or moves within or
near a fluid.
Definitions Cont’.
10. What is a Fluid?
Fluid: A substance in the liquid or gas phase.
A solid can resist an applied shear stress by a static deformation (deforming).
Fluids can be defined as substances that have zero shear modulus or in
simpler terms a fluid is a substance which cannot resist any shear force
applied to it.
A fluid element before deformation. Fluid element after the application of a force
acting tangentially on the top of the element.
Liquid and Gas are both fluids: in contrast to solids they lack the ability to
resist deformation. Because a fluid cannot resist the deformation force, it
moves, it flows under the action of the force. Its shape will change
continuously as long as the force is applied.
11. 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.
What is a Fluid?
12. 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.
13. 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.
14. The arrangement of atoms in different phases:
Inter molecular 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.
(a) molecules are at
relatively fixed positions in
a solid.
(b) groups of molecules
move about each other in
the liquid phase.
(c) individual molecules
move about at random in
the gas phase.
15. Classification of Fluid Motions
Viscous and Inviscid Flows
Laminar and Turbulent Flows
Compressible and Incompressible Flows
Internal and External Flows
Internal Flows
Flows completely bounded by solid surfaces.
Examples: Flow in ducts and vessels; flow in pumps, fans, and
compressors.
Open-channel flow
The internal flow of liquids in which the ducts does not flow full.
Examples: Flow in rivers, irrigation ditches, and aqueducts.
External Flows
Flow over bodies immersed in an unbounded fluid.
Examples: Flow over a submerged submarine, flow over an airplane, and
flow over a gulf ball, etc.
*** Report on Classification of Fluid Motions
16. Number of fluids engineering applications is enormous:
breathing, blood flow, swimming, pumps, fans, turbines,
airplanes, ships, rivers, windmills, pipes, icebergs,
missiles (rockets), engines, filters, jets, and sprinklers,
…….etc.
When you think about fluids engineering applications,
almost everything on this planet either is a fluid or moves
within or near a fluid.
Application Areas of Fluid Mechanics
21. Dimensions and Units
Any physical quantity can be characterized by dimensions.
The magnitudes assigned to the dimensions are called units.
Some basic dimensions such as length L, mass m, time t, and temperature T
are selected as primary or fundamental dimensions, while others such as
velocity V, energy E, and volume V are expressed in terms of the primary
dimensions and are called secondary dimensions, or derived dimensions.
Metric SI system and English system.
Standard prefixes in SI units
Seven fundamental or primary
dimensions and their units in SI
22. Primary Dimensions in International System (SI)
and British Gravitational System (BG)
In fluid mechanics there are only four primary dimensions from
which all other dimensions can be derived: mass, length, time, and
temperature.
23. Secondary Dimensions in Fluid Mechanics
A list of some important secondary variables in fluid mechanics, with
dimensions derived as combinations of the four primary dimensions,
is given in the below Table
24. Some examples of SI and English Units
The SI unit prefixes are used in all branches of
engineering.
The definition of the force units.
Work = Force Distance
1 J = 1 N∙m
1 Btu = 252 cal = 1.0551 kJ
1 kilowatt hour (kWh) = 3.6*106 J
1 N = 1 kg.m/s2
1 Ibf = 32.174 Ibm.ft/s2
1 Ibf = 1 slug.ft/s2
1 Ibf = 4.4482 N
J: Joules
Btu: British thermal units
Cal: calories
25. The relative magnitudes of the force
units newton (N), kilogram-force
(kgf), and pound-force (lbf).
W weight
m mass
g gravitational
acceleration
26. Unity Conversion Ratios
All secondary units can be formed by combinations of primary units.
Force units, for example, can be expressed as
They can also be expressed more conveniently as unity conversion
ratios as:
Dimensional Homogeneity
All equations must be dimensionally homogeneous.
27. A useful theoretical equation for computing the relation between pressure,
velocity, and altitude in a steady flow of a nearly inviscid, nearly
incompressible fluid with negligible heat transfer and shaft work is:
(a) Show that Eq. (1) satisfies the principle of dimensional homogeneity,
which states that all additive terms in a physical equation must have the
same dimensions.
(b) Show that consistent units result without additional conversion factors in
SI units.
(c) Repeat (b) for BG units.
Dimensional Homogeneity Example
30. Conversion Factors
*Although the absolute (Kelvin) and Celsius temperature scales have different starting points, the intervals are the same
size: 1 kelvin =1 Celsius degree. The same holds true for the nonmetric absolute (Rankine) and Fahrenheit scales: 1
Rankine degree = 1 Fahrenheit degree. It is customary to express temperature differences in absolute-temperature units.
