Classification of Fluid Flows:
Types of Fluid Flows
1. Steady and Unsteady flow
2. Uniform and non-uniform flow
3. One, two and three-dimensional flow
4. Rotational or irrotational flow
5. Laminar or Turbulent flow
1. Steady and Unsteady Fluid Flow
a). Steady Flow
o A steady flow is one in which conditions (velocity, pressure and cross-
section) can vary from point to point, but do not change over time.
o In real conditions, it is very rare to have such flows with parameters that
are absolutely constant over time. The parameters usually change over
time but the variance is within a small range such that the average of a
particular parameter remains constant for a fixed period of time.
b). Unsteady Flow
o If at any point of the fluid, the conditions change over time, the flow is
said to be unstable. (In practice there is always a slight difference in
velocity and pressure, but if the average values are constant, the flow is
assumed to be constant.
o A constant flow can be uniform or non-uniform and thus, an unstable
flow can also be uniform or non-uniform. For a steady flow, the discharge
is constant over time and for uniform flow, the area of the cross-section
of the fluid flow through the flow stream is constant.
, 2. Uniform and Non-Uniform Fluid Flow
a). Uniform Flow
o If the flow parameter remains constant with distance along the flow path,
then the fluid flow is uniform flow.
o For a uniform flow, the area of the cross-section of the flow must remain
constant. So a suitable example of uniform flow is the flow of a fluid
through a pipeline of constant diameter. And conversely, to this, the flow
through a pipeline of variable diameter will be essentially non-uniform.
b). Non-uniform Flow
o The fluid flow is non-uniform if the flow parameters change and are
varied at different points on the flow path.
o If at a given moment, the velocity is not uniform at every point then the
flow is non-uniform. (In practice, by this definition, each fluid that flows
near a solid boundary will be non-uniform because the fluid at the
boundary must have a boundary speed, usually zero. However, the flow is
assumed to be uniform if the shape and size of the cross-section of the
fluid stream are constant).
3. One, two and Three-dimensional Fluid Flow
Although in general, all fluids flow in three-dimensional form, varying in
all directions with pressure and velocity and other flow properties, in many
cases the largest change occurs in only two directions or even only in one.
In these cases, changes in the other direction can be effectively ignored so
as to make the analysis more straightforward.
a). One-dimensional Flow
o The flow is one-dimensional if the flow parameters like velocity,
pressure, depth, etc. change only in the direction of flow at a given
moment and not across the cross-section.
Types of Fluid Flows
1. Steady and Unsteady flow
2. Uniform and non-uniform flow
3. One, two and three-dimensional flow
4. Rotational or irrotational flow
5. Laminar or Turbulent flow
1. Steady and Unsteady Fluid Flow
a). Steady Flow
o A steady flow is one in which conditions (velocity, pressure and cross-
section) can vary from point to point, but do not change over time.
o In real conditions, it is very rare to have such flows with parameters that
are absolutely constant over time. The parameters usually change over
time but the variance is within a small range such that the average of a
particular parameter remains constant for a fixed period of time.
b). Unsteady Flow
o If at any point of the fluid, the conditions change over time, the flow is
said to be unstable. (In practice there is always a slight difference in
velocity and pressure, but if the average values are constant, the flow is
assumed to be constant.
o A constant flow can be uniform or non-uniform and thus, an unstable
flow can also be uniform or non-uniform. For a steady flow, the discharge
is constant over time and for uniform flow, the area of the cross-section
of the fluid flow through the flow stream is constant.
, 2. Uniform and Non-Uniform Fluid Flow
a). Uniform Flow
o If the flow parameter remains constant with distance along the flow path,
then the fluid flow is uniform flow.
o For a uniform flow, the area of the cross-section of the flow must remain
constant. So a suitable example of uniform flow is the flow of a fluid
through a pipeline of constant diameter. And conversely, to this, the flow
through a pipeline of variable diameter will be essentially non-uniform.
b). Non-uniform Flow
o The fluid flow is non-uniform if the flow parameters change and are
varied at different points on the flow path.
o If at a given moment, the velocity is not uniform at every point then the
flow is non-uniform. (In practice, by this definition, each fluid that flows
near a solid boundary will be non-uniform because the fluid at the
boundary must have a boundary speed, usually zero. However, the flow is
assumed to be uniform if the shape and size of the cross-section of the
fluid stream are constant).
3. One, two and Three-dimensional Fluid Flow
Although in general, all fluids flow in three-dimensional form, varying in
all directions with pressure and velocity and other flow properties, in many
cases the largest change occurs in only two directions or even only in one.
In these cases, changes in the other direction can be effectively ignored so
as to make the analysis more straightforward.
a). One-dimensional Flow
o The flow is one-dimensional if the flow parameters like velocity,
pressure, depth, etc. change only in the direction of flow at a given
moment and not across the cross-section.
