Wednesday, 14 March 2018

TYPES OF FLUID FLOW IN FLUID MECHANICS

TYPES OF FLUID FLOW IN FLUID MECHANICS

We were discussing the basic definition of kinematics of flow in the subject of fluid mechanics in our recent post. Now we will start a new topic in the field of fluid mechanics i.e. Types of fluid flow with the help of this post.

There are following types of fluid flow as mentioned here.

Steady and unsteady flow

Steady flow

Steady flow is basically defined as the flow in which, the properties of fluid such as density, velocity, pressure at a point do not change with time.

In simple, if a fluid flow is not a function of time then that flow will be termed as steady flow. Flow of water with constant discharge through a pipe line will be considered as steady flow.

 

Un-steady flow

Un-steady flow is basically defined as the flow in which, the properties of fluid such as density, velocity, pressure at a point changes with time.

In simple, if a fluid flow is a function of time then that flow will be termed as unsteady flow. Flow of water with varying discharge through a pipe line will be considered as unsteady flow.

Uniform and non-uniform flow

Uniform flow is basically defined as the flow in which, the properties of fluid such as density, velocity, pressure at a given time do not change with respect to space.

Non-uniform flow is basically defined as the flow in which, the properties of fluid such as density, velocity, pressure at a given time changes with respect to space.

Laminar flow and Turbulent flow

Laminar flow 

Laminar flow is basically defined as that type of flow in which the fluid particles will move along the well defined paths or streamlines. These streamlines will be straight and parallel with each other. Therefore in case of laminar flow, particles will move in laminas or layers, smoothly gliding over each other.

Laminar flow provides the information that fluid flow will be organized, slow, parabolic profile, parallel to vessel walls etc. Laminar flow will not produce any sound.

Turbulent flow

Turbulent flow is basically defined as the flow in which the particles of fluid will move in zig-zag way. As fluid particles will move in zig-zag way in turbulent flow, there will be formation of eddies and that will be responsible for high energy loss. Turbulent flow will produce sound and can be heard also.

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.

 

Compressible and incompressible flow

Compressible flow is basically defined as the flow in which the density of the fluid will be changed from point to point. In simple words we can say that, density of the flowing fluid will not be constant.

Incompressible flow is basically defined as the flow in which the density of the fluid will not changed from point to point. In simple words we can say that, density of the flowing fluid will be constant.
For compressible flow, Density (ρ) constant
For incompressible flow, Density (ρ) = constant

Rotational and irrotational flow

Rotational flow is basically defined as the flow in which fluid particles while flowing along the stream lines will also rotate about their own axis.

irrotational flow is basically defined as the flow in which fluid particles while flowing along the stream lines will not rotate about their own axis.

One, two and three dimensional flow

One dimensional flow

One dimensional flow is basically defined as the flow in which the flow parameters such as velocity will be a function of time and one space co-ordinate only.

For one dimensional steady fluid flow, velocity will be a function of one space co-ordinate only. Variation of velocities in other two mutually perpendicular directions will be negligible.

Two-dimensional flow

Two-dimensional flow is basically defined as the flow in which the flow parameters such as velocity will be a function of time and two rectangular space co-ordinates only.

For two-dimensional steady fluid flow, velocity will be a function of two space co-ordinates only. Variation of velocity in third direction will be negligible.

 

Three-dimensional flow

Three-dimensional flow is basically defined as the flow in which the flow parameters such as velocity will be a function of time and three space co-ordinates.

For three-dimensional steady fluid flow, velocity will be a function of three space co-ordinates.

We will discuss the basic concept of rate of flow or discharge in the subject of fluid mechanics in 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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