Fluid mechanics

FLUID MECHANICSFLUID MECHANICS

Fluid Mechanics is that Fluid Mechanics is that branch of science which branch of science which deals with behaviour of deals with behaviour of

the fluids at rest as well as the fluids at rest as well as in motionin motion

Fluid mechanics can we Fluid mechanics can we divided into 3 divisions:divided into 3 divisions:

Hydrostatics: that studies the mechanics of Hydrostatics: that studies the mechanics of fluids at absolute and relative rest.fluids at absolute and relative rest.

Kinematics: deals with translation, rotation Kinematics: deals with translation, rotation and deformation of fluid without considering and deformation of fluid without considering the force and energy causing such a motion.the force and energy causing such a motion.

Dynamics: that prescribes the relation Dynamics: that prescribes the relation between velocities and acceleration and the between velocities and acceleration and the forces which are exerted by or upon the forces which are exerted by or upon the moving fluids.moving fluids.

What is Fluid ?What is Fluid ?

Matter exist in two principal forms:Matter exist in two principal forms:

• SolidSolid

• FluidsFluids

Fluids are further sub-divided into:Fluids are further sub-divided into:

• Liquid Liquid

• GasGas

For all practical purposes , the For all practical purposes , the liquids and solids can be liquids and solids can be regarded as incompressible.This regarded as incompressible.This means that pressure and means that pressure and temperature have practically no temperature have practically no effect on them.Eg Water, effect on them.Eg Water, Kerosene,petrol etc.Kerosene,petrol etc. But Gases are readily compressible But Gases are readily compressible

fluids.They expand infinitely in the fluids.They expand infinitely in the absence of pressure and contract easily absence of pressure and contract easily under pressure. Eg air ,ammonia etc.under pressure. Eg air ,ammonia etc.

A DAY FULL OF FLUID A DAY FULL OF FLUID MECHANICSMECHANICS

YOU WOKE UP IN THE MORNING AND YOU WOKE UP IN THE MORNING AND THE ROOM IS COOL.THE ROOM IS COOL.

Coolant circulatingCoolant circulating

Inside it and cool Inside it and cool

Air which it givesAir which it gives

is Fluidis Fluid

After that you washed your face After that you washed your face at the sink. The water which at the sink. The water which comes at your tap is fluid and comes at your tap is fluid and has come through the piping has come through the piping system which also comes under system which also comes under fluid mechanics.fluid mechanics.

After that you decided to have After that you decided to have your breakfast. your breakfast. The coolant movinginside the small pipes at the back of yourrefrigerator, and the air circulating inside it are both fluids.

After finishing your breakfast, After finishing your breakfast, You decided to do some cleaning beforeheading to the school. Proper suction of airand filtering the dust requires the knowledge of Fluid Mechanics.

After that you turned on your After that you turned on your T.V to get the morning news.T.V to get the morning news.Nothing good, war againNothing good, war again

UNMANNED AIR VEHICLE USED UNMANNED AIR VEHICLE USED BY US ARMY IN AFGHANISTANBY US ARMY IN AFGHANISTAN

MISSILE AERODYNAMICSMISSILE AERODYNAMICS

Now it’s the time to go to Now it’s the time to go to college, otherwise you will get college, otherwise you will get latelateA mixture of A mixture of fuelfuel like petrol and like petrol and airair is is

forced by atmospheric (or greater) forced by atmospheric (or greater) pressure into the cylinder through pressure into the cylinder through the intake port the intake port

Before your class you went to Before your class you went to PC lab and took a print out of PC lab and took a print out of your assignment. Inkjet your assignment. Inkjet printing also involves fluid printing also involves fluid mechanics.mechanics.

Knowledge of Fluid Mechanics Knowledge of Fluid Mechanics is essential for proper design of is essential for proper design of Ships.Ships.

Otherwise without the proper Otherwise without the proper knowledge of fluid mechanics, knowledge of fluid mechanics, What will happenWhat will happen

In this subject, topic on Model In this subject, topic on Model Studies is there which is very Studies is there which is very important for civil engineers.important for civil engineers.

Model Tests on civil engineering Model Tests on civil engineering structures such as Dams, canals to structures such as Dams, canals to predict the working of full size predict the working of full size structure and river models assist a structure and river models assist a civil engineer in the design of flood civil engineer in the design of flood control structure as well as in the control structure as well as in the analysis of sediment movement in analysis of sediment movement in rivers.rivers.

Significance of Fluid Significance of Fluid MechanicsMechanics• Design of wide range of hydraulic Design of wide range of hydraulic

structures (dams,canals) and machinery ( structures (dams,canals) and machinery ( pumps,turbines).pumps,turbines).

• Fluidic control devices; both pneumatic Fluidic control devices; both pneumatic and hydraulic.and hydraulic.

• Design and analysis of gas turbine , rocket Design and analysis of gas turbine , rocket engine, super sonic aircrafts.engine, super sonic aircrafts.

• Human circulatory system i.e the flow of Human circulatory system i.e the flow of blood in veins and the pumping action of blood in veins and the pumping action of heart. heart.

Ideal Fluid: A fluid is said to be Ideal Fluid: A fluid is said to be ideal if it is assumed to be both ideal if it is assumed to be both incompressible and inviscid incompressible and inviscid (non-viscous).(non-viscous).

Ideal fluid has no surface tension and Ideal fluid has no surface tension and viscosity is zero and no frictional forces viscosity is zero and no frictional forces are set up even during the fluid motion.are set up even during the fluid motion.

Ideal Fluids are imaginary and do not exist in Ideal Fluids are imaginary and do not exist in nature .nature .

Real Fluid: Practical Fluid have Real Fluid: Practical Fluid have surface tension, viscosity and surface tension, viscosity and compressibility.compressibility.

Whenever motion takes place, the Whenever motion takes place, the tangential or shear forces always tangential or shear forces always come into play due to viscosity and come into play due to viscosity and some frictional work is done.some frictional work is done.

Density ()

Density is the mass of the fluid per unit volume

= m/v Units : Kg/m3

Specific Gravity(s):Specific Gravity(s):

The specific gravity is the ratio of the density or specific weight of the fluid to the density or specific weight of

water, at a temperature of 4oC

For Gases the standard fluid is taken either air at 00 C or Hydrogen at the

same temperature.

It is dimensionless quantity.

A Statement that the specific gravity of A Statement that the specific gravity of mercury is 13.6 implies that its mercury is 13.6 implies that its weight (or mass) in 13.6 times that weight (or mass) in 13.6 times that of the same volume of water.of the same volume of water.

In simple words, mercury is 13.6 times In simple words, mercury is 13.6 times heavier than water.heavier than water.

Specific Volume: Represents Specific Volume: Represents the volume per unit mass of the volume per unit mass of fluid.fluid.Specific Volume is the inverse of the Specific Volume is the inverse of the

mass density.mass density.

v= V/mv= V/m or v=1/or v=1/ The concept of specific volume is found The concept of specific volume is found

to be more useful in the study of flow to be more useful in the study of flow of compressible fluids i.e gases.of compressible fluids i.e gases.

Viscosity: It is the property of Viscosity: It is the property of the fluid by virue of which it the fluid by virue of which it offers resistance to shear or offers resistance to shear or angular deformation.angular deformation.

Mollases,tar, glycerine are highly Mollases,tar, glycerine are highly viscous fluids.viscous fluids.

Water,air,petrol have very small Water,air,petrol have very small viscosity and are called thin fluids.viscosity and are called thin fluids.

Newton’s Law of ViscosityNewton’s Law of Viscosity

= (du/dy) (du/dy)

Where, du/dy =velocity gradientWhere, du/dy =velocity gradient

= coefficient of viscosity, absolute viscosity or dynamic viscosity.

Following Observations can be Following Observations can be made from Newton’s viscosity made from Newton’s viscosity Equation:Equation:• Max. shear stress occur when velocity Max. shear stress occur when velocity

gradient is largest and shear stress gradient is largest and shear stress disappears where velocity gradient is disappears where velocity gradient is zero.zero.

• Velocity Gradient becomes small with Velocity Gradient becomes small with distance from the boundary.Consequently distance from the boundary.Consequently the max value of shear stress occurs at the max value of shear stress occurs at the boundary and it decreases from the the boundary and it decreases from the boundary.boundary.