Types of Fluid Flow
Fluid flows can be classified based on several characteristics, as explained below:
6.5.3.1 Steady and Unsteady Flow
- Steady Flow: Fluid properties (velocity, pressure, density, temperature) at any point do not change with time: \[ \left( \frac{\partial \vec{v}}{\partial t} \right)_s = \left( \frac{\partial p}{\partial t} \right)_s = \left( \frac{\partial \vec{a}}{\partial t} \right)_s = 0 \]
- Unsteady Flow: Fluid properties vary with time at a given location.
6.5.3.2 Uniform and Non-Uniform Flow
- Uniform Flow: Velocity does not change with space at any instant: \[ \left( \frac{\partial \vec{v}}{\partial s} \right)_t = 0 \]
- Non-Uniform Flow: Velocity varies with space at a given instant: \[ \left( \frac{\partial \vec{v}}{\partial s} \right)_t \ne 0 \]
6.5.3.3 Rotational and Irrotational Flow
- Rotational Flow: Fluid particles rotate about their own mass center while moving.
- Irrotational Flow: Fluid particles do not rotate about their own mass center.
6.5.3.4 Laminar and Turbulent Flow
- Laminar Flow: Fluid particles move in smooth layers. Viscosity dominates and flow is orderly.
- Turbulent Flow: Fluid particles move chaotically, causing mixing and momentum transfer. Turbulent flow is generally unsteady.
6.5.3.5 Dimensions of Fluid Flow
Flow dimensionality depends on how many spatial coordinates influence the flow parameters:
- Three-Dimensional Flow: Parameters vary with all three coordinates (e.g., flow in a tapered pipe).
- Two-Dimensional Flow: Parameters vary with two coordinates (e.g., flow in a straight pipe).
- One-Dimensional Flow: Parameters vary with only one coordinate (e.g., ideal flow in a straight pipe).
Note: Real pipe flow has velocity variation across the section, so for high accuracy it should be treated as two-dimensional.
6.5.3.6 Compressible and Incompressible Flow
- Compressible Flow: Fluid density varies with space (e.g., high-speed gas flows).
- Incompressible Flow: Fluid density remains constant throughout the flow region (e.g., most liquid flows).