A fluid is a state of matter in which its molecules move freely and do not bear a constant relationship in space to other molecules. In physics, fluid flow has all kinds of aspects: steady or unsteady, compressible or incompressible, viscous or non-viscous, and rotational or irrotational to name a few. Some of these characteristics reflect properties of the liquid itself, and others focus on how the fluid is moving. Fluids are :- Liquid : blood, i.v. infusions) Gas : O2 , N2O) Vapour (transition from liquid to gas) : N2O (under compression in cylinder), volatile inhalational agents (halothane, isoflurane, etc) Sublimate (transition from solid to gas bypassing liquid state) : Dry ice (solid CO2), iodine

1. Types of Fluid Flow

2. Introduction
A fluid is a state of matter in which its molecules move
freely and do not bear a constant relationship in space to
other molecules.
In physics, fluid flow has all kinds of aspects: steady or
unsteady, compressible or incompressible, viscous or
non-viscous, and rotational or irrotational to name a few.
Some of these characteristics reflect properties of the
liquid itself, and others focus on how the fluid is moving.
Fluids are :-
• Liquid : blood, i.v. infusions)
• Gas : O2 , N2O)
• Vapour (transition from liquid to gas) : N2O (under
compression in cylinder), volatile inhalational agents
(halothane, isoflurane, etc)
• Sublimate (transition from solid to gas bypassing
liquid state) : Dry ice (solid CO2), iodine

3. Definition of Flow
Flow is defined as the quantity of fluid
(gas, liquid, vapour or sublimate) that
passes a point per unit time.
A simple equation to represent this is:
Flow (F) = Quantity (Q)
Time (t)
Flow is sometimes written as ∆Q (rate
of change of a quantity).

4. Types of Fluid Flow
Aerodynamic force
Cavitation
Compressible flow
Couette flow
Free molecular flow
Incompressible flow
Inviscid Flow
Isothermal Flow
Laminar Flow

5. Aerodynamic Force
Aerodynamic force is exerted on a body by the air
(or some other gas) in which the body is immersed,
and is due to the relative motion between the body
and the gas. Aerodynamic force arises from two
causes:
• The normal force due to the pressure on the
surface of the body.
• The shear force due to the viscosity of the gas,
also known as skin friction.
Forces on an Aero foil

6. Cavitation
Cavitation is the formation of vapour cavities in
liquid i.e. small liquid free zones that are the
consequence of forces acting upon the liquid.
It usually occurs when a liquid is subjected to rapid
changes of pressure that cause the formation of
cavities where the pressure is relatively low.
When subjected to higher pressure, the voids
implode and can generate an intense shock wave.
Cavitating propeller model
in a water tunnel
experiment

7. Compressible Flow
Compressible flow is the branch of fluid mechanics
that deals with flows having significant changes in fluid
density. Gases, but not liquids, display such behaviour.
To distinguish between compressible and
incompressible flow in air, the Mach number (the ratio
of the speed of the flow to the speed of sound) must be
greater than about 0.3 (since the density change is
greater than 5% in that case) before significant
compressibility occurs.
The study of compressible flow is relevant to high-
speed aircraft, jet engines, rocket motors, hyper loops
high-speed entry into a planetary atmosphere, gas
pipelines, commercial applications such as abrasive
blasting, and many other fields.

8. Couette Flow
Couette flow is the laminar flow of a viscous fluid in
the space between two parallel plates, one of which is
moving relative to the other.
The flow is driven by virtue of viscous drag force acting
on the fluid and the applied pressure gradient parallel
to the plates.
This type of flow is named in honour of Maurice Marie
Alfred Couette, a Professor of Physics at the French
University of Angers in the late 19th century.

9. Free Molecular Flow
Free molecular flow describes the fluid dynamics of
gas where the mean free path of the molecules is
larger than the size of the chamber or of the object
under test.
For tubes/objects of the size of several cm, this means
pressures well below 10−3 Torr. This is also called the
regime of high vacuum. This is opposed to viscous
flow encountered at higher pressures.
In free molecular flow, the pressure of the remaining
gas can be considered as effectively zero. Thus,
boiling points do not depend on the residual pressure.
The flow can be considered to be individual particles
moving in straight lines. Practically, the "vapour"
cannot move around bends or into other spaces
behind obstacles, as they simply hit the tube wall.

10. Incompressible Flow
In fluid mechanics or more generally continuum
mechanics, incompressible flow (isochoric flow) refers
to a flow in which the material density is constant within a
fluid parcel an infinitesimal volume that moves with the
flow velocity. An equivalent statement that implies
incompressibility is that the divergence of the flow
velocity is zero.
Inviscid Flow
An inviscid flow is the flow of an ideal fluid that is
assumed to have no viscosity. In fluid dynamics there are
problems that are easily solved by using the simplifying
assumption of an inviscid flow. The flow of fluids with low
values of viscosity agree closely with inviscid flow
everywhere except close to the fluid boundary where the
boundary layer plays a significant role.

11. Isothermal Flow
Isothermal flow is a model of compressible fluid
flow whereby the flow remains at the same
temperature while flowing in a conduit.
In the model, heat transferred through the walls of
the conduit is offset by frictional heating back into
the flow.
Although the flow temperature remains constant, a
change in stagnation temperature occurs because
of a change in velocity.
The interesting part of this flow is that the flow is
choked at and not at Mach number equal to one as
in the case of many other model such as Fanno
flow. This fact applies to real gases as well as ideal
gases.

12. Laminar Flow
laminar flow (or streamline flow) occurs when a fluid
flows in parallel layers, with no disruption between the
layers.
At low velocities, the fluid tends to flow without lateral
mixing, and adjacent layers slide past one another like
playing cards.
There are no cross-currents perpendicular to the
direction of flow, nor eddies or swirls of fluids. In laminar
flow, the motion of the particles of the fluid is very
orderly with all particles moving in straight lines parallel
to the pipe walls.
Laminar flow is a flow regime characterized by high
momentum diffusion and low momentum convection.