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Thursday, 30 August 2018

DIFFERENCE BETWEEN LAMINAR FLOW AND TURBULENT FLOW


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 
  1. Higher viscosity of fluid 
  2. Lower velocity of fluid flow 
  3. 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 cross-section 
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 non-dimensional 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 stream-line 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 

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