Basics
نﺮﻗ ﺎﺗ • 20
ياﺰﺠﻣ ترﻮﺻ ود ﻪﺑ تﻻﺎﯿﺳ ﻪﻌﻟﺎﻄﻣ :
ﯽﻠﯿﻠﺤﺗ و يرﻮﺌﺗ يﺎﻫ ﻪﺒﻨﺟ – :
نﺎﻧاد ﯽﺿﺎﯾر
ﯽﺑﺮﺠﺗ يﺎﻫ ﻪﺒﻨﺟ – :
ﻦﯿﺳﺪﻨﻬﻣ
و ﻦﻣرﺎﮐ نﻮﻓ ،ﻞﺘﻧاﺮﭘ ،زﺪﻟﻮﻨﯾر ﺮﯿﻈﻧ يا ﻪﺘﺴﺟﺮﺑ ﻦﻘﯿﻘﻘﺤﻣ • ...
ﻪﺘﺨﯿﻣآ ﺪﯾﺎﺑ تﻻﺎﯿﺳ ﻪﻌﻟﺎﻄﻣ ﻪﮐ ﺪﻨﺘﻓﺎﯾرد
ﺪﺷﺎﺑ ﻪﺒﻨﺟ ود ﺮﻫ زا يا :
تﻻﺎﯿﺳ ﮏﯿﻧﺎﮑﻣ ﻢﻠﻋ زﺎﻏآ
لﺎﯿﺳ ﻒﯾﺮﻌﺗ • :
ﯽﻣ ﻪﻣادا ﻞﮑﺷ ﺮﯿﯿﻐﺗ ﻪﺑ ﺪﺷﺎﺑ ﻪﺘﺷاد دﻮﺟو ﯽﺷﺮﺑ ﺶﻨﺗ ﻪﮑﯿﻣﺎﮕﻨﻫ ﺎﺗ ﻪﮐ ﺖﺳا يا هدﺎﻣ
ﺪﻫد .
= ≠
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Basics: special cases of fluid
• Rheology: solid substances such as asphalt resist shear stress for short periods but actually deform slowly and exhibit definite fluid behavior over long periods.
– is the study of the flow of matter, primarily in the liquid state, but also as 'soft solids' or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force.
• Multiphase flows: liquids and gases can coexist in two-phase mixtures
• Critical point: in some situations the distinction between a liquid and a gas blurs. This is the case at temperatures and pressures above the so- called critical point of a substance
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Basics
• hydrostatic condition:a fluid at rest with a state of zero shear stress
• Fluid mechanics is the study of fluids either in motion (fluid dynamics) or at rest (fluid statics)
• gases and liquids are classified as fluids
– Liquid: form a free surface
– Gas: no free surface, no definite volume
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Basics: applications
Breathing
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Basics: applications
Blood Flow
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Basics: applications
Swimming
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Basics: applications
Cycling
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Basics: applications
Pump/Turbine/Fan
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Basics: applications
Airfoil
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Basics: applications
Airplane
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Basics: applications
Ship
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Basics: applications
Engine
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Basics: applications
Windmill
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Basics
لﺎﯿﺳ • : ﻢﺋاد درﻮﺧﺮﺑ لﺎﺣ رد يﺎﻬﻟﻮﮑﻟﻮﻣ
لﺎﯿﺳ رﺎﺘﻓر ﯽﺳرﺮﺑ لﻮﺻا • :
ﺎﻬﻟﻮﮑﻟﻮﻣ ﻖﯿﻗد رﺎﺘﻓر ﻞﯿﻠﺤﺗ :
يرﺎﻣآ ﮏﯿﻧﺎﮑﻣ :
،ﻻﺎﺑ ﻪﻨﯾﺰﻫ ،هﺪﯿﭽﯿﭘ رﺎﯿﺴﺑ
ﯽﻧﻻﻮﻃ نﺎﻣز ﻞﺣ هار • :
رد ﻪﺘﺳﻮﯿﭘ ﻂﯿﺤﻣ ﮏﯾ ترﻮﺼﺑ ار لﺎﯿﺳ ،اﺰﺠﻣ يﺎﻬﻟﻮﮑﻟﻮﻣ هﺪﯿﭽﯿﭘ ﯽﻌﻗاو تاﺮﺛا ﯽﺳرﺮﺑ يﺎﺟ ﻪﺑ
ﻢﯾﺮﯿﮔ ﯽﻣ ﺮﻈﻧ .
ﻪﺘﺳﻮﯿﭘ ﻂﯿﺤﻣ شور • Fluid as a continuum: if the unit volume is large compared with the cube of the :
molecular spacing.
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Basics
• The limiting volume ∗ is about 10 for all liquids and for gases at atmospheric pressure.
• Most engineering problems are concerned with physical dimensions much larger than this limiting volume
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Basics: Dimensions and Units
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Basics: Dimensions and Units
• each additive term in an equation must have the same dimensions The Principle of Dimensional Homogeneity
Bernoulli’s incompressible equation
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Basics: Properties of a Fluid
• Any characteristic of a system is called a property. Some familiar properties:
– pressure P, temperature T, volume V, and mass m
• Less familiar characteristic:
– viscosity, thermal conductivity, modulus of elasticity.
• Properties are considered to be either intensive or extensive.
• Intensive properties are those that are independent of the mass of a system,
– such as temperature, pressure, and density.
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Basics: Properties of a Fluid
• Extensive properties are those whose values depend on the size of the system.
– Total mass, total volume V, total momentum
• Extensive properties per unit mass are called specific properties. Some examples of specific properties are specific volume (v = V/m) and specific total energy (e = E/m).
• The state of a system is described by its properties.
• But we know from experience that we do not need to specify all the properties in order to fix a state.
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Basics: Properties of a Fluid
The state of a simple system is completely specified by two independent, intensive properties.
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Basics: Properties of a Fluid
• Pressure: Pressure is the (compression) stress at a point in a static fluid
• Differences or gradients in pressure often drive a fluid flow
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Basics: Properties of a Fluid
• Temperature:Temperature T is related to the internal energy level of a fluid.
• Density: The density of a fluid is its mass per unit volume.
• Density is highly variable in gases and increases nearly proportionally to the pressure level.
• Density in liquids is nearly constant;
≅ 1000
• increases only 1% if the pressure is increased by a factor of 220.
• Thus most liquid flows are treated analytically as nearlyincompressible
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Basics: Properties of a Fluid
• specific weight of a fluid is its weight per unit volume:
• Specific gravity, denoted by SG, is the ratio of a fluid density to a standard reference fluid, usually water at 4C (for liquids) and air (for gases):
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Basics: Properties of a Fluid
ﺖﺳا ﺶﻧﺮﮐ خﺮﻧ و لﺎﯿﺳ ﻪﺑ هﺪﺷ لﺎﻤﻋا ﯽﻠﺤﻣ ﺶﻨﺗ نﺎﯿﻣ يا ﻪﻄﺑار ﺖﺟﺰﻟ ﺎﯾ ﻪﺘﯾزﻮﮑﺴﯾو • .
ﺖﺳا نﺪﺷ يرﺎﺟ ﺮﺑاﺮﺑ رد لﺎﯿﺳ ﺖﻣوﺎﻘﻣ ناﺰﯿﻣ ﺮﮕﻧﺎﯾﺎﻤﻧ ﺖﯿﻤﮐ ﻦﯾا • .
،ﺪﺷﺎﺑ ﺮﺗ جﺰﻟ لﺎﯿﺳ رﺪﻘﭼ ﺮﻫ
ﺪﻫد ﯽﻣ نﺎﺸﻧ دﻮﺧ زا نﺪﺷ يرﺎﺟ ﻞﺑﺎﻘﻣ رد يﺮﺘﺸﯾ ﺖﻣوﺎﻘﻣ
• We can easily move through air, which has very low viscosity. Movement is more difficult in water, which has 50 times higher viscosity. Still more resistance is found in SAE 30 oil, which is 300 times more viscous than water.
Viscosity and Other Secondary Properties
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Basics: Properties of a Fluid
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Basics: Properties of a Fluid
ﯽﻧﺎﻤﻟا • زا
لﺎﯿﺳ ار
رد ﺮﻈﻧ ﺪﯾﺮﯿﮕﺑ ﻪﮐ
ﺖﺤﺗ ﮏﯾ
يوﺮﯿﻧ )
ﺶﻨﺗ ( ﯽﺷﺮﺑ راﺮﻗ
دراد . ﻪﺘﺴﺑ ﻪﺑ
ﺖﻣوﺎﻘﻣ
لﺎﯿﺳﯽﯾﻻﺎﺑ ﺢﻄﺳ ﺶﻨﺗ لﺎﻤﻋاﻪﺠﯿﺘﻧ رد .ﺪﯾآ ﯽﻣ دﻮﺟﻮﺑيدﻮﻤﻋ ﻪﺤﻔﺻ ﺎﺑ ﯽﺷﺮﺑ ﻪﯾوازﮏﯾ نﺎﯾﺮﺟ ﻞﺑﺎﻘﻣ رد ﺎﺑ ﺖﻣوﺎﻘﻣ ﻞﯿﻟد ﻪﺑ ﻢﯿﻨﮐ ﺖﮐﺮﺣ ﺮﺘﻨﯿﯾﺎﭘ يﺎﻫ ﻪﯾﻻ ﺖﻤﺳ ﻪﺑ ﻪﭼﺮﻫ و ﺪﺑﺎﯾ ﯽﻣ نﺎﯾﺮﺟ ﯽﻨﯿﻌﻣ ﺖﻋﺮﺳ
ﻪﯾﻻ .دﻮﺷ ﯽﻣ ﻪﺘﺳﺎﮐ نﺎﯾﺮﺟ ﺖﻋﺮﺳ ناﺰﯿﻣ زا لﺎﯿﺳ يﺎﻫ
رد • ﯽﻫوﺮﮔ زا
تﻻﺎﯿﺳ ﺪﻨﻧﺎﻣ
،بآ ﻦﻏور و
اﻮﻫ ﮏﯾ ﻪﻄﺑار ﯽﻄﺧ
نﺎﯿﻣ ﺶﻨﺗ
ﯽﺷﺮﺑ لﺎﻤﻋا
هﺪﺷ و
خﺮﻧ :ﯽﻨﻌﯾ .دراد دﻮﺟو هﺪﺷ دﺎﺠﯾا ﺶﻧﺮﮐ
ﺎﺑ • ﻪﺟﻮﺗ ﻪﺑ
ﻞﮑﺷ ﯽﻣ
ناﻮﺗ ﺖﺷﻮﻧ :
∝
tan ∝
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Basics: Properties of a Fluid
ﺎﺑ • ضﺮﻓ كﺪﻧا
ندﻮﺑ تاﺮﯿﯿﻐﺗ ﻪﯾواز
:
ﺐﯾﺮﺿ • ﻦﯾا
ﺐﺳﺎﻨﺗ ﻪﺘﯾزﻮﮑﺴﯾو
ﺎﯾ ﺖﺟﺰﻟ مﺎﻧ
دراد .
= ∝
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Basics: Properties of a Fluid
دﻮﺷ ﯽﻣ هﺪﯿﻣﺎﻧ ﯽﻨﺗﻮﯿﻧ لﺎﯿﺳ ،ﺪﻨﮐ يوﺮﯿﭘ ﻪﻄﺑار ﻦﯾا زا شرﺎﺘﻓر ﻪﮐ ﯽﻟﺎﯿﺳ ﺮﻫ • .
• Sir Isaac Newton postulated this resistance law in 1687.
ﺖﺟﺰﻟ ﺮﮕﯾد ﺪﺣاو • poize
ﺖﺳا .
= = = { }
1 = 0.1 .
: ( . . )
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Basics: Properties of a Fluid
a shear layer, or boundary layer, near a solid wall.
The shear stress is proportional to the slope of the velocity profile
and is greatest at the wall.
the velocity u is zero relative to the wall:
This is called the no-slip condition and is characteristicof all viscous fluid flows.
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Basics: Properties of a Fluid
• The viscosity of Newtonian fluids is a:
thermodynamic property
• and varies with temperature and pressure.
• Generally speaking, the viscosity of a fluid increases only weakly with pressure.
• Temperature, has a strong effect.
• in most engineering work we neglect the pressure variation
↑ 1 − 50 → ↑ (10%)
: ↑→ ↑ : ↑→ ↓
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Basics: Properties of a Fluid
• Gas viscosity increases with temperature. Two common approximations are the power law and the Sutherland law:
• 0: known viscosity at a known absolute temperature (usually 273 K).
Variation of Viscosity with Temperature
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Basics: Properties of a Fluid
• Liquid viscosity decreases with temperature and is roughly exponential
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Basics: Properties of a Fluid
• Fluids that do not follow the linear law of shear stress-velocity gradient are called non-newtonian and are treated in books on rheology
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Basics: Properties of a Fluid
• The primary parameter correlating the viscous behavior of all Newtonian fluids is the dimensionless Reynolds number:
• where V and L are characteristic velocity and length scales of the flow.
• Very low Re indicates viscous creeping motion, where inertia effects are negligible.
• Moderate Re implies a smoothly varying laminar flow.
The Reynolds Number
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Basics: Properties of a Fluid
• the mass units cancel
kinematic viscosity
=
: ( )
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Flow Pattern
• A classic problem is the flow induced between a fixed lower plate and an upper plate moving steadily at velocity V,
• The clearance between plates is h,
• Fluid is Newtonian
• Fluid does not slip at either plate
• If the plates are large, this steady shearing motion will set up a velocity distribution u(y), with
= = ; =
Flow between Plates
Couette Flow
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Flow Pattern
• no pressure variation in the flow direction
• shear stress is constant throughout the fluid
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Flow Pattern
• velocity profile between the plates is given by = ℎ
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Surface Tension
• liquid, being unable to expand freely, will form an interface with a second liquid or gas.
ﺪﺘﻓا ﯽﻣ قﺎﻔﺗا زﺎﮔ و ﻊﯾﺎﻣ كﺮﺘﺸﻣ ﺢﻄﺳ رد ﯽﺤﻄﺳ ﺶﺸﮐ • .
ﻊﯾﺎﻣ نﺎﺴﮑﯾ يﺎﻬﻟﻮﮑﻟﻮﻣ ﻦﯿﺑ ﻪﺑذﺎﺟ • )
ﯽﮕﺘﺳﻮﯿﭘ (
زﺎﮔ و ﻊﯾﺎﻣ نﺎﺴﮑﯾﺮﯿﻏ يﺎﻬﻟﻮﮑﻟﻮﻣ ﻦﯿﺑ ﻪﺑذﺎﺟ و • )
ﯽﮔﺪﻨﺒﺴﭼ (
دﻮﺷ ﯽﻣ هﺪﯿﻣﺎﻧ .
ﺪﻨﻨﮐ ﯽﻣ ﯽﺜﻨﺧ ار ﺮﮕﯾﺪﮑﯾ ﯽﮕﺘﺳﻮﯿﭘ يﺎﻫوﺮﯿﻧ ﻊﯾﺎﻣ ﻞﺧاد رد • .
ﻪﺑ طﻮﺑﺮﻣ ﯽﮔﺪﻨﺒﺴﭼ يﺎﻫوﺮﯿﻧ زا ﺪﻨﻨﮐ ﯽﻣ ﺮﺛا ﻦﯿﯾﺎﭘ زا ﻪﮐ ﯽﮕﺘﺳﻮﯿﭘ يﺎﻫوﺮﯿﻧ ﻊﯾﺎﻣ دازآ ﺢﻄﺳ رد ﯽﻟو • دﻮﺷ ﯽﻣ ﺮﺘﺸﯿﺑ ﻻﺎﺑ رد زﺎﮔ ﺪﻧﻮﺷ ﯽﻣ ﯽﺤﻄﺳ ﺶﺸﮐ ﺚﻋﺎﺑ و
.
Surface Tension
Cohesion Adhesion
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Surface Tension
دﻮﺷ ﯽﻣ ﯽﻓﺮﻌﻣ لﻮﻃ ﺪﺣاو ﺮﺑ وﺮﯿﻧ ترﻮﺼﺑ ﯽﺤﻄﺳ ﺶﺸﮐ • .
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Flow Pattern
مﺮﺟ ﻪﺑ يﺪﻣﺎﺟ ﻪﻧاﻮﺘﺳا • 2.5 Kg
دﺰﻐﻟ ﯽﻣ ﻦﯿﯾﺎﭘ ﺖﻤﺳ ﻪﺑ يا ﻪﻟﻮﻟ ﻞﺧاد رد .
و هدﻮﺑ رﻮﺤﻣ ﻢﻫ ﻼﻣﺎﮐ ﻪﻟﻮﻟ و ﻪﻧاﻮﺘﺳا
دراد دﻮﺟو ود نآ حﻮﻄﺳ ﻦﯿﺑ ﻦﻏور زا يا ﻪﯾﻻ .
ﺖﺳا هﺪﺷ هداد ﻦﻏور ﺖﺟﺰﻟ ﺐﯾﺮﺿ .
ﺖﺳﺪﺑ ار ﻪﻧاﻮﺘﺳا يﺪﺣ ﺖﻋﺮﺳ
ﺪﯾروآ .
• = 7 × 10 .
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Flow Pattern
ﺪﺷﺎﺑ ﯽﻄﺧ ﻦﻏور رد ﺖﻋﺮﺳ ﻞﯿﻓوﺮﭘ ﻪﮐ ﻢﯿﻨﮐ ﯽﻣ ضﺮﻓ • .
= − 0
74.0 − 73.8 2
= 10000 [1 ]
= = 7 × 10 10000 = 70 [ ]
= → 2.5 × 9.81 = 70 ( )(0.0738)(0.150)
= 10.07
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Properties of a Fluid
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