# Fluid Mechanics Introduction-2

FLUID MECHANICS INTRODUCTION-2

Fluid Mechanics is a science which deals all aspects of  fluids. It studies the fluids whether in motion or static. Fluid is a common name to liquids, vapors and gases.

Three parts of fluid mechanics

• Fluid statics

It deals with forces applied by fluids at rest. This fluid force is pressure. Pressure is a normal force exerted by a fluid per unit area. It is called the static pressure of the fluid. Some laws are used in fluid statics. These laws are

Pascal’s law

It states that the pressure applied by an enclosed liquid will be transmitted equally in all directions.

Newton’s Law

It is applied to a static fluid. Thus, ΣF = ma = 0 for a static fluid.

ΣFx = ΣFy = ΣFz = 0. It deals with equilibrium of forces on a fluid.

Buoyancy Law (Archimedes’ principle)

States that a body completely or partially submerged in a fluid (liquid or gas) AT REST is acted upon by an upward buoyant force. The magnitude of which is equal to the weight of the fluid displaced by the body.

(b)Fluid Kinematics

Deals with fluids in motion without considering forces or energy acting. In this, we study displacement, velocity and acceleration. The other name of kinematics is geometry of motion. In this, we study ideal fluid, real fluid, in-compressible and compressible fluid. Thus, we also study various types of flows. For example,

(i) Laminar flow

(ii) Turbulent flow

(v) Uniform flow

(vi) Non-uniform flow

(vii) Rotational flow

(viii) Ir-rotational flow

(ix) One, two and three dimensional flows

There are two ways to study fluid mechanics. Out of Lagrangian and Eulerian methods, Eulerian method is used as it is relatively easy to apply. It concerns velocity field and continuity equation.

© Fluid Dynamics deals with fluids in motion with forces/energy acting on the moving fluids.

Three types of fluids

• Liquids are in-compressible. There is no effect of pressure and temperature. Examples of liquid are water, milk, kerosene oil, petrol, fatty oils etc.
• Vapor is compressible. Vapors are effected by pressure and temperature. It is studied only with the help of tabular data and charts.  Gas laws are not applicable to vapors. Examples of vapors are steam and refrigerants.
• Gases are compressible. These are effected by pressure and temperature. It is studied with gas laws and universal equation. Examples of gases are air, oxygen, nitrogen, hydrogen etc.

EXAMPLES OF MOVING FLUIDS

1. Water flowing in pipe lines at home or factory
2. Refrigerant flowing in a refrigerator or air conditioner
3. Water flowing in water turbines and pumps
4. Steam flowing in pipes to steam turbines
5. Gas flowing to gas turbines
6. Blood flowing in the human body

FLUID MECHANICS STUDY APPROACH

NOTE: Why we consider the motion of a fluid particle in a fluid motion?

There is a basic difference between the motion of a solid and the motion of a fluid. A solid body is compact and moves as one element. There is no relative motion between the particles of a solid body. Thus, we study the motion of the entire body. Therefore, there is no necessity to study the motion of any particle of a solid body. But in fluids, we consider the motion of individual particles. Because, there is relative motion between various fluid particles.

Prototypes help in the study of fluid mechanics. Further, prototypes are small size working objects for pumps, turbines, submarines, airplanes and dams. These prototypes should have geometric, dimensional, kinematic and dynamic similarities. Of course, study is carried out with empirical equations using dimensionless numbers.