We were discussing the basic concept of kinetic
energy correction factor and momentum correction factor, power
absorbed in viscous flow, viscous resistance of journal bearings,
viscous
resistance of foot step bearings and viscous resistance of collar bearings, in the subject of fluid mechanics, in our recent posts.
Now we will go ahead to find out the basics of
turbulent flow and we will also find here the difference between laminar flow
and turbulent flow, in the subject of fluid mechanics, with the help of this
post.
Laminar Flow
Laminar flow is basically defined as a flow in which
fluid particles will move along the straight parallel path in layers or laminae.
Fluid particles will move along the straight parallel paths in such a way that
the paths of individual fluid particles do not cross those of neighboring
particles.
Laminar flow will take place when flow velocity will
be lower and viscosity of fluid will be high i.e. Laminar flow will take place
only at low velocities and when fluid viscosity is high.
In case of laminar flow, motion of the fluid particles
will be very orderly and all fluid particles will move in straight parallel
paths parallel to the pipe walls.
Therefore let us see here the simple definition of Laminar flow
Laminar flow is basically defined as that type of
fluid flow in which the fluid particles move along well defined paths or stream
lines and all the stream lines are straight and parallel.
Factors responsible for laminar fluid flow
Following factors are responsible for laminar fluid
flow
 Higher viscosity of fluid
 Lower velocity of fluid flow
 Less flow area
Example of laminar fluid flow
Fluid flow through pipe line of uniform cross
sectional area
Flow of blood in small veins
Laminar Flow
Turbulent flow
Fluid particles will not move in straight and
parallel paths, when fluid will be less viscous and velocity of fluid flow will
be high. Fluid particles will move in random manners and therefore there will
be general mixing of fluid particles. Such type of fluid flow will be termed as
turbulent flow.
Therefore let us see here the simple definition of Turbulent flow
Turbulent flow is basically defined as that type of flow
in which the fluid particles move in a zig zag way. Fluid particles will not
move in straight and parallel paths, fluid particles will move in random
manner.
Example of turbulent flow
Flow of water in the river at the time of flood
Flow through the pipe of different crosssection
Turbulent flow
Reynolds’s has explained that the transition of flow
from laminar to turbulent will not only depend over the mean velocity of fluid
flow but also on a dimensionless quantity i.e. Reynolds’s number.
Let us consider we have one pipe and
fluid is flowing through this pipe. Type of fluid flow will be determined on
the basis of a nondimensional number i.e. Reynolds’s number.
Reynolds’s number, Re = ρVD/μ
Where,
D = Diameter of pipe through which fluid
is flowing
V= Velocity of fluid flow
ρ = Density of the fluid
μ = Viscosity of the fluid
If Reynolds’s number is less than 2000,
fluid flow will be considered as laminar fluid flow. Laminar flow is also
termed as viscous flow or streamline flow.
If Reynolds’s number is more than 2000,
fluid flow will be considered as turbulent fluid flow.
If Reynolds’s number is in between 2000
and 4000, fluid flow will be considered as transitional fluid flow.
For more detailed post based on types of
fluid flow could be secured here i.e. “Types of fluid flow in fluid mechanics”.
Difference between Laminar flow and Turbulent flow
Following table shows the basic
difference between laminar flow and turbulent flow.
Laminar Flow

Turbulent flow

Smooth streamlines and highly ordered
motion

Velocity fluctuations and highly disordered motion

Particles are in straight and parallel
path lines

Particles are in irregular path lines

Low velocity

High velocity

Viscosity plays an important role in
laminar flow

Inertia plays an important role in turbulent flow

Velocity profile shown as parabolic
curve

Velocity profile shown as logarithm curve

Can be steady or unsteady

It is always unsteady

Can be one, two or three dimensional

It is always three dimensional

Further we will go ahead to see the
Reynolds experiment, in the subject of fluid mechanics, with the help of our
next post.
Do you have any suggestions? Please write in comment
box.
Reference:
Fluid mechanics, By R. K. Bansal
Image courtesy: Google
Image courtesy: Google