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7/29/2019 Intruduction to Fluid Dynamics
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SME 1313 Fluid Mechanics I
CHAPTER 1INTRODUCTION
By
Ummikalsom Abidin
C24-316FKM, UTM
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SME 1313 Fluid Mechanics I
Introduction
Fluid Mechanics
Fluid Statics- fluid at rest
- deals with forcesapplied by fluids at rest
Fluid Dynamics
- fluid in motion
Hydrostatic forceson submerged bodies
e.g dam, tanksstoring fluid,automation actuators
Buoyant forceapplied by fluids onsubmerged orfloating bodies
e.g ships,
submarines
Hydrodynamics
e.g liquid flow inpipes and openchannel(hydraulics),pumps,hydroturbine
s, water coolingsystem
Gas dynamics
e.g gas turbines,flow of air over abody(aerodynamics) aircraft, rockets,
automobiles
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SME 1313 Fluid Mechanics I
Introduction
Naturally occuring flows Meteorology
Oceanography
Hydrology
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SME 1313 Fluid Mechanics I
What is fluid?
Fluid is a substance that deforms continuously underthe application of a shear (tangential) stress nomatter how small the shear stress may be.
t1 t2
F F
t0
t2>t1>t0
(a) (b)
Behavior of (a) solid and (b) fluid, under the action of a constantshear
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SME 1313 Fluid Mechanics I
What is fluid?
Fluids comprise the liquid and gas (orvapor) phases
Distinction between solid,liquid and gas
StrongestMolecules are relatively
fixed position
Solid
WeakestMolecules move about atrandom in the gas phaseGas
ModerateGroups of molecules moveabout each other in theliquid phase
Liquid
Intermolecularbonds
Atom Arrangement
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SME 1313 Fluid Mechanics I
What is fluid?Normal to surface
Force acting on areadA
Tangent to surface
Fn
dA Ft
Normal stress: = Fn/dA
Shear stress: = Ft/dA
The normal stress and shear stress at the surface of a fluid element. For fluids at
rest, the shear stress is zero and the pressure is the only normal stress
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SME 1313 Fluid Mechanics I
No-slip Condition A fluid in direct contact with a solid sticks to the surface due
to viscous effects, and there is no slip.
The flow region adjacent to the wall in which the viscous effects(and thus the velocity gradients) are significant is called
boundary layer.Uniform approach
velocity, V
Relative velocities of
fluid layers
Zero velocity atthe surface
Plate
A fluid flowing over stationary surface comes to a complete stopat the surface because of the no-slip condition
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Viscous vs. Inviscid Regions of Flow
Viscous Flow Region flows in which the frictional effect issignificant
Inviscid Flow Region viscous forces are negligibly small
compared to inertial or pressure forces
Inviscid flow region
Viscous flow
region
Inviscid flow region
The flow of an originally uniform fluid stream over a flat plate, and the regions of viscous flow (next to theplate on both sides) and inviscid flow (away from the plate)
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Internal vs. External Flow Internal flow flows in which the fluid is completely
bounded by solid surface
e.g flow in a pipe or duct
Dominated by the influence of viscosity throughout the flowfield
External flow flows in which the fluid is unbounded over
solid surfaces e.g flow over a plate, wire, sphere object
Viscous effects are limited to boundary layers near solidsurfaces and to wake regions downstream of bodies
* Open-channel flow the flow of liquids in a duct in which the liquid ispartially filled and there is a free surface e.g rivers, irrigation channels
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows Compressible vs. Incompressible Flow
Incompressible Flow density of the fluid remains nearly
constant throughout
liquids, gases at low speeds
density changes of gas flows are under 5% or when Ma0.3 Mach number,
Ma = V = Speed of flow
c Speed of sound Ma=1 (Sonic), Ma1(Supersonic), Ma>>1
(Hypersonic)
(Speed of sound=346 m/s)
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Laminar vs. Turbulent Flow
In 1880s, Osborn Reynolds conducted an experiment to seeflow patterns
Tank arranged as above with a pipe taking water from the centre into which dye is injected through aneedle
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SME 1313 Fluid Mechanics I
Classification of Fluid FlowsFilament of dye
Laminar (viscous)
Transitional
Turbulent
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Reynolds number,Re=ud
Laminar flow Re
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Natural (or unforced) vs. Forced Flow
Forced Flow fluid is forced to flow over a surface or in apipe by external means such as pump or a fan
Natural Flow any fluid motion is due to natural means such
as buoyancy effect, where warmer (and thus lighter) fluidrises and cooler (and thus denser) fluid falls
Schlieren image of a hot water (left) and ice water (right)in a glass
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Steady vs. Unsteady Flow
Steady Flow no change of fluid properties (velocity,pressure) at a point with time
Devices that are intended for continuous operation e.g
turbines, pumps, boilers, condensers
Unsteady Flow fluid properties change at a point with time
Transient used for developing flows
t1=5 s
V1=10 m/s
t2=10 s
V2=10 m/s
t1=5 s
V1=10 m/s
t2=10 sV2=11 m/s
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows
Uniform vs. Non-uniform Flow
Uniform Flow no change of fluid properties with locationover a specified region
Non-uniform Flow if at a given instant, fluid propertieschange with location over a specified region
V1=10 m/s V2=10 m/s
V1=10 m/s V2=11 m/s
or V=10 m/s
orV1=10 m/s
V2=10 m/s
1
2
2
1
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows Steady uniform flow
Conditions do not change with position and with time e.g flow ofwater in a pipe of constant diameter at constant velocity
Steady non-uniform flow Conditions change from point to point in the stream but do not
change with time e.g flow in tapering pipe with constant velocity atinlet, but velocity change along the length of the pipe toward theexit
Unsteady uniform flow At a given instant of time, the conditions at every point are the
same, but will change with time e.g pipe of constant diameterconnected to a pump pumping at a constant rate which is thenswitched off
Unsteady non-uniform flow Every condition of the flow may change from point to point and
with time at every point e.g waves in channel
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows One-, Two-, and Three-Dimensional Flows
1-D Flow flow parameters (such as velocity, pressure, depth)vary in one primary dimensions
2-D Flow - flow parameters vary in two primary dimensions
3-D Flow - flow parameters vary in three primary dimensions
The development of the velocity profile in a circular pipe, V=V(r,z) and thus theflow is 2-D in the entrance region, and becomes 1-D downstream when the velocity
profile fully develops and remain unchanged in the flow direction, V=V(r)
z
Developing velocity profile,V(r,z)
Fully developed velocityprofile, V(r)
r
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SME 1313 Fluid Mechanics I
Classification of Fluid Flows The dimensionality of the flow also depends on the choice of
coordinate system and its orientation Rectangular coordinates, V(x,y,z)
Cylindrical coordinates, V(r,,z)
Higher dimensionality should be considered if only very highaccuracy is required
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SME 1313 Fluid Mechanics I
Application Areas of Fluid Mechanics
Human body (Bio-fluid Mechanics) Cardiovascular system
Artificial heart
Pulmonary system Breathing machine
Building Water supply system
Sewerage system
Heating and air-conditioning
Aerodynamics forces and flow fields aroundstructure
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SME 1313 Fluid Mechanics I
Application Areas of Fluid Mechanics
Automobiles Hydraulic brakes, power steering, automatic
transmission
Fuels line, fuel pump, fuel injectors
Lubrication systems
Cooling systems
Air-conditioning
Aerodynamics design
Aircraft Aerofoil design
Gas turbine
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SME 1313 Fluid Mechanics I
Application Areas of Fluid Mechanics
Ship, submarines, hovercraft Hydrodynamics design
Buoyancy and stability
Industry Cooling of electronics
Automation system
Recreational Badminton shuttle and golf ball aerodynamics
Geophysical fluid dynamics Meteorology Oceanography
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SME 1313 Fluid Mechanics I
System and Control Volumes System quantity of matter or a region in space chosen for
study
Surroundings mass or region outside the system
Boundary Real or imaginary surface that separates the system
from its surroundings (fixed or movable)
SYSTEM
SURROUNDINGS
BOUNDARY
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SME 1313 Fluid Mechanics I
System and Control Volumes Closed System (Control Mass)
Consists of a fixed amount of mass, and no work, can cross theboundary
Energy in the form of heat and work can cross the boundary
E.g piston-clinder device Open System (Control Volume)
Both mass and energy can cross the boundary
E.g compressor, turbine, nozzle, car radiator
Imaginaryboundary
Realboundary
CV
(a nozzle) CV
Imaginaryboundary
Imaginaryboundary
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SME 1313 Fluid Mechanics I
Dimensions and Units Any physical quantity can be characterized by dimensions
Magnitude assigned to the dimensions are called units
Primary or fundamental dimensions
mole (mol)Amount of matter
candela (cd)Amount of light
ampere (A)Electric of current
kelvin (K)Temperature
second (s)Time
kilogram (kg)Mass
meter (m)Length
UnitDimension
The seven fundamental (or primary) dimensions and their units in SI
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SME 1313 Fluid Mechanics I
Dimensions and Units Derived or secondary dimensions are dimensions obtained from
combination of primary dimensions
Most used derived dimensions
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SME 1313 Fluid Mechanics I
SI Units Metric SI (from Le Systeme International dUnites) or
International System SI system was produced by General Conference of Weights and
Measures in 1960
SI is a simple and logical system and widely being used forscientific and engineering work in most of the industrializednations
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SME 1313 Fluid Mechanics I
SI Units
pico, p10-12
nano, n10-9
micro, 10-6
milli, m10-3
centi, c10-2
deci, d10-1
deka, da101hecto, h102
Kilo, k103
mega, M106
giga, G109tera, T10
12
PrefixMultiple
Standard prefixes in SI units
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SME 1313 Fluid Mechanics I
Dimensional Homogeneity In engineering, all equations must be dimensionally
homogeneouswhere every term in an equation musthave the same unit
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SME 1313 Fluid Mechanics I
Problem-Solving Technique Step 1:Problem Statement
State briefly and concisely (in your own words) theinformation given and the quantities to be found
Step 2:Schematic
Draw a schematic of the system or control volume to beused in the analysis.
Indicate any energy and mass interactions with thesurroundings
Listing the given information on sketch Step 3:Assumptions and Approximations
State any assumptions and approximations made to simplifythe problem to make it possible to obtain a solution
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SME 1313 Fluid Mechanics I
Problem-Solving Technique Step 4:Physical Laws
Apply all the relevant basic physical laws and principle andreduce them to their simplest form by utilizing theassumptions made
Step 5:Properties Determine the unknown properties at known states
necessary to solve the problem from property relations ortables
Step 6:Calculations
Substitute the known quantities into the simplified relationsand perform the calculations to determine the unknown Pay attention to the units and unit cancellations Give appropriate number of significant digits
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SME 1313 Fluid Mechanics I
Problem-Solving Technique Step 7:Reasoning, Verification, and Discussion
Check to make sure that the results obtained are reasonableand intuitive and verify the validity of the questionableassumptions
Repeat the calculations that resulted in unreasonable values
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