Classification of Fluid

Classification of Fluid


a) Ideal fluid:

It is hypothetical which represents frictionless flow i.e. fluid without any viscosity. It is also called inviscid fluid. In ideal fluid the internal forces at any internal section are always normal to the section, even during motion. Hence the forces are purely pressure forces.

b) Real fluid:

In a real fluid tangential or shearing force always come into being whenever the motion takes place, thus giving the rise to fluid friction, also known as viscosity.


a) Compressible fluid:

Fluids which will change in volume with the application of force are known as compressible fluid. Gases are compressible.

b) Incompressible fluid:

It implies fluids with constant density i.e. it will not change in volume with the application of force. Though liquids are slightly compressible they are usually assumed to be incompressible.
a) Newtonian fluid: A Newtonian fluid is a fluid whose stress versus strain rate curve is linear and passes through the origin. The constant of proportionality is known as the viscosity.
A simple equation to describe Newtonian fluid behavior is
   t is the shear stress exerted by the fluid [Pa]
   ยต is the fluid viscosity - a constant of proportionality [Pa·s]
is the velocity gradient perpendicular to the direction of shear [ s-1]
For a Newtonian fluid, the viscosity, by definition, depends only on temperature and pressure (and also the chemical composition of the fluid if the fluid is not a pure substance), not on the forces acting upon it.
b) Non-Newtonian fluid: A non-Newtonian fluid is a fluid whose flow properties are not described by a single constant value of viscosity. Many polymer solutions and molten polymers are non-Newtonian fluids. In a non-Newtonian fluid, the relation between the shear stress and the strain rate is nonlinear, and can even be time-dependent.


The viscosity of a fluid is a measure of its resistance to shear or angular deformation. The friction forces in fluid flow result from the cohesion &momentum interchange between molecules in fluid.
Viscosity depends on temperature. But this property is different for liquid & gas. As temperature increases, the viscosities of all liquids decrease, while the viscosities of all gases increase.
Reason: This is because the force of cohesion, which diminishes with temperature, predominates in liquids, while with gases the predominating factor is the interchange of molecules between the layers of different velocities. Thus a rapidly moving molecule shifting into a slower-moving layer tends to speed up later. And a slow-moving molecule entering a fast-moving layer tends to slow down the faster-moving layer. This molecular interchange sets up a shear, or produces a friction force between adjacent layers. Increased molecular activity at higher temperatures causes the velocity of gases to increases with temperature.

Classification of flow

a)Laminar /streamline/ viscous flow:

It occurs when a fluid flows in parallel layers, with no disruption between the layers. The fluid appears to move by the sliding of laminations of infinitesimal thickness relative to the adjacent layer.

b)Turbulent flow:

The main characteristics of turbulent flow is its irregularity, there being no definite frequency, as in wave action, and no observable pattern.
Turbulent flow

a)Steady flow:

A steady flow is one in which all conditions at any point in a stream remain constant with respect to time, but the conditions may be different at different points. True steady flow is found only in laminar flow.

b)Unsteady flow:

An unsteady flow is one in which all conditions at any point in a stream do not remain constant with respect to time.

a)Uniform flow:

A truly uniform flow is one in which the velocity is the same in both magnitude direction at a given instant at every point in the fluid.

b) Non uniform flow:

A non-uniform flow is one in which the velocity is not same in magnitude or direction at a given instant at every point in the fluid.

a) Rotational flow:

It implies the flow where the fluid particles rotate about their own axis.
Rotational flow

b) Irrotational flow :

It implies the flow where the fluid particles do not rotate about their axis, they only retain their orientation.
Irrotational flow

Other Definitions

Path lines:

It is the trace made by a single particle over a period of time.

Stream lines:

Streamlines show the mean directions of a number of particles at the same instant of time. Streamlines are a family of curves that are instantaneously tangent to the velocity vector of the flow.

Streak lines:

Streak lines are the locus of points of all the fluid particles that have passed continuously through a particular spatial point in the past. Dye steadily injected into the fluid at a fixed point extends along a streak line. These can be thought of as a "recording" of the path a fluid element in the flow takes over a certain period. The direction the path takes will be determined by the streamlines of the fluid at each moment in time.


According to the American Congress on Surveying and Mapping (ACSM), Surveying is the science and art of making all essential measurements to determine the relative position of points and/or physical and cultural details above, on, or beneath the surface of the Earth, and to depict them in a usable form, or to establish the position of points and/or details.

Surveying has been an essential element in the development of the human environment since the beginning of recorded history (ca. 5000 years ago) and it is a requirement in the planning and execution of nearly every form of construction. Its most familiar modern uses are in the fields of transport, building and construction, communications, mapping, and the definition of legal boundaries for land ownership.

Introduction to Civil Engineering

Civil engineering is a professional engineering discipline that deals with the design, construction and maintenance of the physical and naturally built environment, including works such as bridges, roads, canals, dams and buildings.Civil engineering is the oldest engineering discipline after military engineering,and it was defined to distinguish non-military engineering from military engineering.It is traditionally broken into several sub-disciplines including environmental engineering,geotechnical engineering, structural engineering, transportation engineering, municipal or urban engineering, water resources engineering, materials engineering, coastal engineering,surveying, and construction engineering.Civil engineering takes place on all levels: in the public sector from municipal through to federal levels, and in the private sector from individual homeowners through to international companies.

History of the civil engineering profession

Engineering has been an aspect of life since the beginnings of human existence. Civil engineering might be considered properly commencing between 4000 and 2000 BC in Ancient Egypt and Mesopotamia when humans started to abandon a nomadic existence, thus causing a need for the construction of shelter. During this time, transportation became increasingly important leading to the development of the wheel and sailing. The construction of Pyramids in Egypt (circa 2700-2500 BC) might be considered the first instances of large structure constructions. Other ancient historic civil engineering constructions include the Parthenon by Iktinos in Ancient Greece (447-438 BC), the Appian Way by Roman engineers (c. 312 BC), and the Great Wall of China by General Meng T'ien under orders from Ch'in Emperor Shih Huang Ti (c. 220 BC).The Romans developed civil structures throughout their empire, including especially aqueducts, insulae, harbours, bridges, dams and roads.

Until modern times there was no clear distinction between civil engineering and architecture, and the term engineer and architect were mainly geographical variations referring to the same person, often used interchangeably.In the 18th century, the term civil engineering began to be used to distinguish it from military engineering.
The first self-proclaimed civil engineer was John Smeaton who constructed the Eddystone Lighthouse.[4][6] In 1771 Smeaton and some of his colleagues formed the Smeatonian Society of Civil Engineers, a group of leaders of the profession who met informally over dinner. Though there was evidence of some technical meetings, it was little more than a social society.
n 1818 the Institution of Civil Engineers was founded in London, and in 1820 the eminent engineer Thomas Telford became its first president. The institution received a Royal Charter in 1828, formally recognising civil engineering as a profession. Its charter defined civil engineering as the art of directing the great sources of power in nature for the use and convenience of man, as the means of production and of traffic in states, both for external and internal trade, as applied in the construction of roads, bridges, aqueducts, canals, river navigation and docks for internal intercourse and exchange, and in the construction of ports, harbours, moles, breakwaters and lighthouses, and in the art of navigation by artificial power for the purposes of commerce, and in the construction and application of machinery, and in the drainage of cities and towns.
The first private college to teach Civil Engineering in the United States was Norwich University founded in 1819 by Captain Alden Partridge. The first degree in Civil Engineering in the United States was awarded by Rensselaer Polytechnic Institute in 1835.The first such degree to be awarded to a woman was granted by Cornell University to Nora Stanton Blatch in 1905.

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