Fluid Mechanics Lectures

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Fluid Engineering MechanicsFluid Engineering Mechanics

Course Code: CIVL213Course Code: CIVL213

Dr.Dr. MajedMajed SubhiSubhi AbuAbu SharkhSharkh

College of Engineering and ArchitecturalCollege of Engineering and Architectural

Civil and Environmental Engineering DepartmentCivil and Environmental Engineering Department

University ofUniversity of NizwaNizwa

Semester, Fall 2010Semester, Fall 2010--20112011


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Chapter OneChapter One

Basic ConceptsBasic Concepts

1.1 Introduction.1.1 Introduction.

1.2 Classification of Fluids.1.2 Classification of Fluids.

1.3 Fluid Science Applications.1.3 Fluid Science Applications.

1.4 Dimensions, Units, and Systems of Measurement1.4 Dimensions, Units, and Systems of Measurement..

1.51.5 Fluid Properties: mass density; specific volume; specificFluid Properties: mass density; specific volume; specific

weight; specific gravity; relative density.weight; specific gravity; relative density.

1.6 Viscosity.1.6 Viscosity.

1.7 Bulk Modulus of Elasticity.1.7 Bulk Modulus of Elasticity.


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Introduction-Concepts:

Mechanics: is the oldest physical science that deals with

both stationary and moving bodies (substances either

solids or non-solids) under the influence of forces.

Statics: the branch of mechanics that deals with bodies atrest.

Dynamics: the branch that deals with bodies in motion is

called dynamics.

Fluid Mechanics: is defined as the science that deals withthe 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.

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Introduction:

The matteris exists in two states: Solid and Fluid

Solid: is a substance when subjected to shear stress is not

deform or yield until internal resistance to deformation

equals the externally applied stress. Ex. wood, steel, etc.

Fluid: is a substance which deforms or yield continuously

when shear stress is applied to it, no matter how small it

is. Ex. water, gas, air, oil, etc.

The fluid is also divided in two states:Liquids: water, oil, blood, honey, glycerin, paint, etc

Gases: air, gas hydrogen, etc.

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Difference Between Solids and Fluids:

Distinction between a solid and a fluid is made on the basis

of the:

1) Distances between different molecules: intermolecular

bonds are strongest in solids and weakest in fluids. The

molecules in solids are closely packed together, whereas

in fluid they are separated by relatively large distances.

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2) Substances ability to resist an applied stress: shear (or

tangential) stress that tends to change its shape.

A solid can resist an applied shear stress by deforming,

whereas a fluid deforms continuously under the influenceof shear stress, no matter how small.

In solids, stress is proportional to strain, but in fluids

stress is proportional tostrain rate

. When a constantshear force is applied, a solid eventually stops deforming,

at some fixed strain angle, whereas a fluid never stops

deforming and approaches a certain rate of strain.

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Distinction between solid and fluid?

Solid: can resist an applied shear by deforming. Stress is

proportional to strain.

Fluid: deforms continuously under applied shear. Stress

is proportional to strain rate.

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Classification of Fluids:

Fluid can be subdivided into liquids and gases.

Liquids:

Occupy a certain volume and have free surface.

The volume does not change appreciably when subjectedto normal stress or temperature.

Gases:

Have a tendency to expand and fill container in which

they are kept; they don not have free surface.

The volume change considerably when subjected to

normal stress or temperature.

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Fluid Behavior:

Stress is defined as the force per unit area.

Normal component: normal stress In a fluid at rest,

the normal stress is called pressure.

Tangential component:

shear stress.

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Classification of Fluids:

A liquid takes the shape of the container it is in and forms

a free surface in the presence of gravity.

A gas expands until it encounters the walls of the

container and fills the entire available space. Gases

cannot form a free surface.

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Fluid Science Applications:

RiverHydraulics Blood Pumping Air Pollution

Means of Transportation

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Fluid Science Applications:

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Dimensions and Units:

In fluid mechanics we must describe various fluid

characteristics in terms of certain basic quantities such as

length, time and mass.

A dimension is the measure by which a physical variableis expressed qualitatively, i.e. length is a dimension

associated with distance, width, height, displacement.

Basic of Primary quantities: Length L, Time T, Mass M.

We can derive any secondary quantity from the primary

quantities i.e. Force = (mass) x (acceleration) : F= M LT-2

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Dimensions and Units:

A unit is a particular way of attaching a number to the

qualitative dimension: Systems of units can vary from

country to country, but dimensions do not.

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Primary

Dimension

System

International (SI)

British

Gravitational (BG)

English

Engineering (EE)

Mass [M] Kilogram (kg) Slug Pound-mass (lbm)

Length [L] Meter (m) Foot (ft) Foot (ft)

Time [T] Second (s) Second (s) Second (s)

Temperature [] Kelvin (K) Rankine (R) Rankine (R)

Force [F] Newton (N Pound (lb) Pound-force (lbf)

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Fluid Properties:

Density of a fluid (Rho): is the amount of mass per unit

volume of a substance:

= m / V (kg/m3) and (M/L3)

For liquids: weak function of

temperature and pressure

For gases: strong function of T and P

Specific weight (Gama): is the amount of weight per unit

volume of a substance.= weight/volume= W / V = mg/V = g

Dimensionally: M/L2T2 and the unit is N/m3

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Fluid Properties:

Specific Volume : is the volume per unit weight and hence

= Volume/weight

Dimensionally: L2T2 /M and the unit is m3/N

Specific Gravity or Relative Density SG: is the ratio of mass

density to mass density of pure water at standard

pressure of 101.325 N/m2 and temperature of 4oC.

SG = / H2O, 4oC

Pressure P: is the force acting on unit area normal to it.

P = lim F/ A (unit: N/m2= Pascal)

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Fluid Properties:

Temperature:

Temperature Scale

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Fluid Properties:

A flow is classified as:

Incompressible Fluid: if the density of the fluid remains

nearly constant, the flow is incompressible. Liquid flows

are typically incompressible, (= constant).

Compressible Fluid: if the density of the fluid change, the

flow is compressible. Gas flows are often compressible,

especially for high speeds , (= change).

Mach number, Ma = V/c is a good indicator of whetheror not compressibility effects are important.

Ma < 0.3: Incompressible; Ma < 1: Subsonic;

Ma=1:Sonic;Ma > 1 : Supersonic; Ma >> 1 : Hypersonic

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Viscosity:

Viscosity: is that property of fluid by which it offers

resistance to shear acting on it. According to Newtons

law of viscosity the shear force F acting between two

layers of fluid is proportional to difference in their

velocities u and area A, and inversely proportional tothe distance y between them as shown in the Figure-1.

Figure-1: Shear and Velocity Distribution

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Viscosity:

F = A u / y

The fluid ability to resist the shear force; i.e. the resulted

shear stress is directly proportional to the rate of strain.

The constant is a measure to the fluid VISCOSITY.

is called the dynamic or absolute viscosity or viscosity

of a fluid, where, = N. s . m-2 or kg/m.s

One gm/cm.s dynamic viscosity is known as poise (P)

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Viscosity:

The ratio of the viscosity and the density often occurs in

fluid flow situation. This ratio,

= /

Is called the kinematic viscosity and has units m2/s. Thisgives a measure of the amount of viscosity per unit mass.

It is a matter of taste whether the kinematic or dynamic

viscosity is the primary quantity.

The other unit of kinematic viscosity is stocks,

1 stocks = 1 cm2/s

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Bulk Modulus of Elasticity:

Modulus of Elasticity:A property that is commonly used to

describe compressibility of fluids.

Where v is the specific volume and dv is the change in v

due to increase dP. E is expressed in N/m2 or kN/m2.

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Fluid Mechanics Lectures