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__Basic Concepts of Fluid __

## Introduction and Basic Concepts

- Mechanics:- It is a branch of physical science that deals with energy and forces and their effect on both stationary and moving bodies.

- Statics:- It is a branch of mechanics that deals with bodies at rest.

- Dynamics:- It is a branch of mechanics that deals with bodies in motion.

- Fluid mechanics:- It deals with the behaviour of fluids at rest or in motion, and the interaction of fluids with solids or other fluids at the boundaries.

- Fluid statics:- It is a branch of fluid mechanics that deals with fluids at rest.

- Hydrodynamics:- It deals with the motion of fluids that can be approximated as incompressible.

- Hydraulics:- It is a sub-category of hydrodynamics which deals with the flow of fluids in pipes and open channels.

- Gas dynamics:- It deals with the flow of fluids that undergo significant density change.

- Aerodynamics:- It deals with the flow of gases over bodies such as aircraft and automobiles.

- Meteorology, Oceanography and Hydrology:- It deals with the naturally occurring flows.

- Stress:- Force per unit area is called stress.

- Normal stress:- Normal component of force acting on a surface per unit area is called normal stress.

- Shear stress:- Tangential component of force acting on a surface per unit area is called shear stress.

- Pressure:- Normal stress in a fluid at rest is called pressure.

- Fluid:- A fluid is a substance which deforms continuously under the influence of shear stress. In solids, stress is proportional to strain but in fluids, stress is proportional to strain rate.

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__Explanatory Video__

## Virtual Fluid Balls (VFB) Concept

- Fluid balls differ in size, volume and mass.

- Number of VFB depends on the complexity of fluid flow problems.

- Fluid balls may disintegrate for representing the flow complexity.

## No-slip condition

- A fluid in direct contact with a solid surface sticks to the surface and there is no slip. This condition is called a No-slip condition.

## Applications of Fluid Mechanics

- Its applications can be seen in natural flows, weather, pipe systems, cars, aircraft, spacecraft, human body, power plant, boats, ships, wind turbines, etc.

## Classification of Fluid flows

- Viscous flow:- The flow in which viscous forces are significant is called viscous flow.

- Inviscid flow:- The flow in regions where viscous forces are negligibly small in comparison to inertial or pressure force is called inviscid flow.

- External flow:- The flow of an unbounded fluid over a surface is called external flow.

- Internal flow:- The flow of a fluid which is completely bounded by a solid surface is called internal flow.

- Steady flow:- The flow in which there is no change at any point with time is called steady flow.

- Unsteady flow:- The flow in which there is a change at any point with time is called unsteady flow.

- Periodic flow:- A kind of unsteady flow in which flow oscillates about a steady mean is called a periodic flow.

- Forced flow:- When a fluid is forced to flow over a surface or in a pipe by external means such as a pump, this type of flow is called a forced flow.

- Natural flow:- The fluid motion due to natural means such as buoyancy effect is called natural flow. Ex:- Rise of warmer fluid and fall of cooler fluid.

- Laminar flow:- The flow in which ordered fluid motion is characterized by smooth layers of the fluids is called laminar flow. Ex:- Oils at low velocities.

- Turbulent flow:- The flow in which highly disordered fluid motion typically occurs at higher velocities and is characterized by velocity fluctuations is called turbulent flow. Ex:- Low viscosity fluids such as air at high velocities.

- Transitional flow:- The flow alternating between laminar and turbulent flow is called transitional flow.

- Compressible flow:- The flow in which the density of the fluid changes is called compressible flow. Ex:- High-speed gas flow.

- Incompressible flow:- The flow in which the density of the fluid remains nearly constant throughout. Ex:- Fluid flow when Ma<0.3.

## Mach number

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- When analyzing rockets, aircraft which involve high-speed gas flows, the flow speed is often expressed as Mach number.

Speed of flow

- Mach number = _____________

Speed of sound

- Ma=1 (Sonic flow)

- Ma>1 (Supersonic flow)

- Ma<1 (Sub-sonic flow)

- Ma>>1 (Hypersonic flow)

- When analyzing rockets, aircraft which involve high-speed gas flows, the flow speed is often expressed as Mach number.

- Mach number = _____________

- Ma=1 (Sonic flow)

- Ma>1 (Supersonic flow)

- Ma<1 (Sub-sonic flow)

- Ma>>1 (Hypersonic flow)

## One, Two, Three- Dimensional Flows

- The flow field is characterized by velocity distribution.

V= V (x, y, z, t) or V= V (r, θ, z, t)

- The flow is said to be 1D, 2D or 3D if the flow velocity varies in 1D, 2D or 3D directions.

- Variation of velocity in certain directions is small relative to other directions and is ignored.

*Self Typed

*Source- Internet, Books, Self-Analysis