Types of Fluid Flow

Types of Fluid Flow | Mechanical Engineering Insights

Table of Contents

1. Steady Flow and Unsteady Flow

Steady Flow

In steady flow, fluid properties (such as velocity, pressure, and density) at any point do not change with time.

Example: Water flowing through a pipe at a constant rate.

\frac{∂v}{∂t} = 0, \frac{∂p}{∂t} = 0, \frac{∂ρ}{∂t} = 0;

Unsteady Flow

In unsteady flow, the fluid properties at a point change with time.

Example: Water draining from a tank as the water level drops.

\frac{∂v}{∂t} \neq 0, \frac{∂p}{∂t} \neq 0, \frac{∂ρ}{∂t} \neq 0;

2. Uniform Flow and Non-uniform Flow

Uniform Flow

In uniform flow, the velocity at any given time does not change with respect to space.

Example: Fully developed flow in a long, straight pipe of constant diameter.

(\frac{\partialv}{∂s}) = C = 0

Non-Uniform Flow

In non-uniform flow, the velocity changes with respect to space.

Example: Flow through a converging nozzle where velocity increases.

(\frac{\partialv}{∂s}) = C \neq 0

3. Laminar Flow and Turbulent Flow

Laminar Flow

In laminar flow, fluid particles move along well-defined paths or streamlines. The streamlines are straight and parallel.

Example: Honey dripping slowly from a spoon.

Turbulent Flow

In turbulent flow, fluid particles move in a zigzag or irregular manner. The flow is characterized by mixing and eddies and is determined by a non-dimensional parameter known as the Reynolds number.

Example: Rapid water flow in a rocky river.

Note: A higher Reynolds number typically indicates turbulent flow, while a lower number suggests laminar flow.

4. Compressible Flow and Incompressible Flow

Compressible Flow

Compressible flow occurs when the density of the fluid changes from point to point.

Example: Supersonic flight where shock waves form due to significant changes in air pressure and density.

Incompressible Flow

In incompressible flow, the density of the fluid is assumed constant.

Example: Water flow in a hydraulic system.

5. Rotational Flow and Irrotational Flow

Rotational Flow

In rotational flow, fluid particles rotate about their own axis as they move along the streamlines.

Example: Flow through a kitchen sink or flow through a hole.

Irrotational Flow

In irrotational flow, fluid particles move along streamlines without rotating about their own axis.

Example: Idealized flow around an airfoil (outside the boundary layer).