Ch1 Introduction to FLuid Mechanics

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Chapter 1

Introduction

Prepared By:

Dishank Upadhyay

Mechatronics DepartmentTeamLease Skills University

Vadodara


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Content

• Solid, Liquid & Gas

• Ideal and real fluids

• Continuum

• Units & Dimensions


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What is Fluid Mechanics?

• Study of

– Physically behavior of fluid and fluid system and the laws governing

this behavior

– action of forces on fluids and of the resulting flow pattern


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Fluid MechanicsFluid Mechanics

Hydrostatic

Studies the mechanics of

fluids at absolute andrelative rest; the fluid

elements are free fromshearing stress

Kinematics

Deals with translation,

rotation and deformation offluid elements withoutconsidering the force and

energy causing such a force

Dynamics

This prescribes the relationbetween velocities and

accelerations and the forceswhich are exerted by orupon the moving fluids


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Solid, Liquid and Gases• Matter exists in two principal forms

– Solid

– Fluid• Liquid

• Gas

• Electricity ????• Features

1. Molecular structure and spacing, inter molecular bonds.

2. Mass & Volume with temperature and pressure. – The solid has volume and shape

– The liquid has volume but no shape

– A gas has neither

3. Change of pressure and temperature on matters. – Gas can readily condensed to a liquid, we call it vapor such as steam and ammonia

4. Deformation due to different forces. – The tendency of continuous deformation of a fluid is called fluidity

– and the act of continuous deformation is called fluid


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Liquid and GasLiquid Gas

A given mass of liquid has a definite volume

independent of the size or shape of the

container; however, its changes its shape

easily and acquires the shape of its container

A given mass of gas has no fixed volume; and

it expands continuously to completely fill any

container in which it is placed.

A free surface is formed if the volume of the

container is greater than that of the liquid

No free surface is formed

Liquid can be regarded as incompressible for

all practical purposes

Gases are readily compressible

Pressure and temperature changes have

practically no effect on the volume of a

liquid.

A gas expands infinitely in the absence of

pressure and contracts easily under pressure

Water, kerosene, petrol etc. are liquids Air, ammonia, carbon dioxide etc. are gases


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Ideal & Real Fluids• Ideal Fluid

– it is said if it is assumed to be both incompressible andinviscid (non-viscous).

– further it has no surface tension.

– for an inviscid fluid, viscosity is zero and no frictionalforces are set up even during fluid motion.

• = 0

• = ; = −

= ∞

• = 0


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Ideal & Real Fluids• Ideal Fluid are imaginary and does not exist in

nature.

• however, most common fluids such as air andwater have very low value of viscosity and can be

treated as ideal fluids for all practical purposes

without introducing any appreciable error.• water is incompressible so it is more nearer to

ideal fluid than air.


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Ideal & Real Fluids• Real Fluid or Practical fluid

– they have viscosity ( ), Compressibility (K) and

surface tension ( ).• whenever motion takes place, the tangential or

shear forces always comes into play due to

viscosity and some frictional work is done.


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Continuum• Fluid consist of

– Discrete molecules

– Analysis of fluid flow problems made by continuous media

•

Properties – All voids or cavities, microscopic or macroscopic, which may occur in

fluids are ignored

– physical properties are than continuous point to pont and can be givenin Algebraic function of space and time coordinates

•

“A continuous and homogeneous fluid medium is calledcontinuum.”

• from the continuum view point, the overall properties and thebehaviour of fluids can be studied without regards for its atomicand molecular structure.


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Significance of Fluid Mechanics

• Applications in many

area like

1. Design of wide range ofhydraulic structures

– Dams, Canals

– Machineries like –

Pumps, Turbines and

fluid couplings


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2. Fluidic control

devices both hydraulics

and pneumatics


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3. Design and analysis

of gas turbines, rocket

engines, conventionaland rocket engines,

conventional and

supersonic aircraft.


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5. Human circulatory

system i.e. flow of blood

in veins and the vital roleit plays in variety of

engineering application.


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Units and Dimensions• Dimension:

– it describes the measurable qualities or characteristics of anobject such as mass, length and time (M,L,T) and

Temperature (θ).• Unit

– accepted standard for measuring the dimension or quality.

• As per SI System (Fundamental Units) – Mass (M) : Kilogram : Kg

– Length (L) : Metre : m

– Time (T) : Second : s

– Temperature (θ): Kelvin or Celcius : K or ◦C


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Units and Dimensions

• Derived Units are:

– Density :

– Newton :

– pascal :

– joule :

– watt :

• Fundamental Units are:

– kg/m^3

– kg.m/s^2 or N

– N/m^2 = Pa

– Nm = J

– J/s = W


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Methods of placing limit dimensions

• Method 3

– Maximum and minimumsizes are directly indicatedabove the dimension line.

– When assembled parts aredimensioned, fit is indicatedby the basic size common to

both the components. – Follow by the hole tolerance

than by the shaft tolerance.


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Commonly used derived unitsDerived term Dimension SI UnitArea [L2] m2

Volume [L3] m3

Velocity [LT-1] m/s

Acceleration [LT-2] m/s2

Force [MLT-2] N

Pressure (Stress) [ML-1T-2] N/m2 = Pascal (Pa)

Energy [ML2T-2] N/m = Joule (J)

Power [ML2T-3] J/s = Watt (W)

Density [ML-3] Kg/m3

Viscosity [ML-1T-1] Kg/ms

Surface tension [MT-1] N/m


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SI Units Multipliers• to facilitate working with magnitudes which

may be multipliers or sub multipliers of SIunits, we use prefix before the units to suit aparticular situation.

• e.g. terra, mega, kilo, milli, micro and pico.

• Additional Comments on SI system1. units with name of scientist always in small

letters – e.g. newton – not Newton

2. there are to be no dots and dashes. – Nm is right, not N.m or N-m

3. While writing plurals, do not add s to thesymbols. – kg is right , not kgs

Factor Prefix1012 Tera, T

109 Giga, G

106 Mega, M

103 Kilo, k

10-1 Deci, d

10-2 Centi, c

10-3 Milli, m

10-6 Micro,

10-9 Nano, n

10-12 Pico, p

10-15 Femto, f

10-18 Atto, a


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Thank You

• Chapter 1 : Introduction

• Prepared By:

– Dishank Upadhyay

Mechatronics DepartmentTLSU,Vadodara

Ch1 Introduction to FLuid Mechanics

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Transcript of Ch1 Introduction to FLuid Mechanics