Types Of Flows

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Types of Flows

1.    Steady and unsteady flow.
2.    Uniform and non-uniform flow.
3.    Laminar and turbulent flow.
4.    Compressible and incompressible flow.
5.    Rotational and irrotaional flow
6.    One, two and three-dimensional flow

Steady and Unsteady Flow:

•    The flow in which fluid characteristics like velocity, pressure, density etc. at a point does not changes with time is called as steady flow.

•    E.g flow of water with constant discharge through a pipeline is as steady flow.

∂v / ∂t = 0           ∂ρ / ∂t = 0            ∂ρ / ∂t = 0

•    The flow in which fluid characteristics like velocity, pressure, density etc. at a point changes with time is called as unsteady flow.

•    E.g flow of water with varying discharge though a pipe is as unsteady flow.

   ∂v / ∂t ≠ 0      ∂ρ / ∂t ≠ 0          ∂ρ / ∂t ≠ 0

Uniform and Non-uniform Flow:

•    The flow in which velocity at a given time does not change with respect to space (length of direction of flow is called as uniform flow.

•    E.g flow through a long straight pipe of uniform diameter is considered as uniform flow.

∂v / ∂s = 0

•    The flow in which velocity at a given time changes with respect to space (length of direction of flow) is called as non-uniform flow.

•    E.g flow through a long pipe with varying cross section is consider as non-uniform flow.

∂v / ∂s ≠ 0

(a) Uniform velocity (b) Non - uniform velocity

Laminar and Turbulent Flow:

•    The flow in which the adjacent layer do not cross to each other and move along the well defined path is called as laminar flow.

•    E.g. flow of blood in small veins, flow of ail in bearings, flow in porous media, flow of highly.

•    The flow in which the adjacent layers cross each other and do not move along the well define path is called as turbulent flow.

•    E.g. flow through a river or canal, smoke from chimney, smoke from a cigarette.

•    If Reynolds’s number is less than 2000, then the flow is laminar.

•    If Reynolds’s number is more than 4000, then the flow is turbulent.

•    If Reynolds’s number is between 2000 to 4000, then the flow is transit.

Reynold’s Number:

Reynold’s number is defined as the ratio fo the inertia force of the fluid to the viscous force.

Reynold’s number = Inertia force / Viscous force = ρVL / μ

Compressible and Incompressible Flow:

•    The flow in which the density does not remain constant for the fluid flow is called as compressible flow.

•    E.g. problems involving flight of rockets, aircrafts, flow fo air in problems concerned with tubomachines, compressor blades, flow of gases through openings like nozzles.

•    The flow in which the density is constant for the fluid flow is called as incompressible flow.

•    E.g. problems involving liquids i.e. hydraulics problems, flow of gases in machines like fans and blowers.

Rotational and Irrigational Flow:

•    The flow in which the fluid particle while flowing along stream lines, also rotate about their own axis is called as rotational flow.

•    E.g. motion of liquid in a rotating cylinder (forced vortex) as rotational flow.

•    The flow in which the fluid particle while flowing along streamlines, do not rotate about their own axis is called as irrigational flow.

•    E.g. flow of liquid in an emptying wash-basin (free vortex) as a rotational flow.

(a) Rotational motion (b) Irrotational motion

One, Two and Three-dimensional Flow:

•    The flow in which the velocity is the function of time and one space co-ordinate (x) is called as One-dimensional flow.

•    E.g. flow through the pipe is consider as a one dimensional flow.

u = f(x),            v = 0,                  w = 0

•    The flow in which the velocity is the function of time and to space co-ordinate (x,y,) is called as two-dimensional flow/

•    E.g viscous flow between parallel plates of large extent, flow at the middle part of airplane wing, flow over a long spillway, flow below long weirs are consider as two-dimensional flow.

u = f₁(x,y),              v = f₂ (x,y),              w = 0

•    The flow is converging or diverging pipes or open channels are as three dimensional flow. Flow in a river, flow at a inlet of a nozzle etc. are the example of three-dimensional flow.

u = f₁ (x,y,z),              v = f₂ (x,y,z),                  w = f₃ (x,y,z) 0

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