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Intro on Fluid Dynamics

March 10, 2011

Fluid:

Fluid is substance(it may be liquid, or gas) that can continually deforms(flows) under an applied shear stress.

Basic properties of the fluid:

Temperature, pressure, mass, specific volume and density.

Why fluid flows:

Fluid particles are not rigidly attached to one another. So If we apply a force on it, it will continually deform that is called flows

Classification of fluids:

Fluids have been classified on the basis of density and viscosity

S.NO Type of fluid Density Viscosity
1 Ideal fluid constant zero
2 Incompressible fluid constant zero or non-zero
3 Inviscid fluid constant or variable zero
4 Real fluid Variable non-zero
5 Newtonian fluid constant or variable non-zero and
6 Non Newtonian fluid constant or variable
7 Compressibe fluid variable zero or non-zero

 

Important types of flows:

Laminar (streamline)  flows

Laminar flow is also referred to as streamline or viscous flow.   These terms are descriptive of the  flow  because,  in  laminar  flow,  (1)  layers  of  water  flowing  over  one  another  at  different speeds  with  virtually  no  mixing  between  layers,  (2)  fluid  particles  move  in  definite  and observable paths or streamlines, and (3) the flow is characteristic of viscous (thick) fluid or is one in which viscosity of the fluid plays a significant part.

Turbulent flows

Turbulent flow is characterised by the irregular movement of particles of the fluid.   There is no definite  frequency  as  there  is  in  wave  motion.   The  particles  travel  in  irregular  paths  with  no observable pattern and no definite layers.

Steady and unsteady flows:

  • steady: A steady flow is one in which the conditions (velocity, pressure and cross-section) may differ from point to point but DO NOT change with time.
  • unsteady: If at any point in the fluid, the conditions change with time, the flow is described as unsteady. (In practise there is always slight variations in velocity and pressure, but if the average values are constant, the flow is considered steady.

Uniform and non-uniform flows:

  • uniform flow: If the flow velocity is the same magnitude and direction at every point in the fluid it is said to be uniform.
  • non-uniform: If at a given instant, the velocity is not the same at every point the flow is non-uniform. (In practice, by this definition, every fluid that flows near a solid boundary will be non-uniform – as the fluid at the boundary must take the speed of the boundary, usually zero. However if the size and shape of the of the cross-section of the stream of fluid is constant the flow is considered uniform.)

Rotational and Irrotational flows:

  • Rotational flow: A flow in which the fluid particles go on rotating about their own axes, while flowing, is said to be rotational.
  • Ir-rotational flow:A flow in which the fluid particles do not rotate about their own axes, while flowing, is said to be rotational.

Barotropic flow:

In meteorology, a barotropic atmosphere is one in which the pressure depends only on the density and vice versa, so that isobaric surfaces (constant-pressure surfaces) are also isopycnic surfaces (constant-density surfaces).

A barotropic flow is a generalization of the barotropic atmosphere described above: It is a flow in which the pressure is a function of the density only and vice versa.

2 Comments leave one →
  1. ajaa permalink
    September 20, 2012 8:51 am

    nice information in very nice way

  2. bss permalink
    October 17, 2012 7:05 am

    really very very good………………….

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