Understanding Different types of Fluid Flows

In this article, we are going to discuss some important terms used in fluid mechanics. In fluid mechanics, students deal with the study of fluid flows. Do you know what are the different types of fluid flows? What are some common types of fluid flows that a civil engineer or mechanical engineer should know about? 

Types of Fluid Flows

There are many types of fluid flows that we should know about being a civil engineer. Some of the general categories of fluid flow  are given below:

1. Difference between Viscous and In-viscid flow

The fluid flow in which there are significant frictional effects is treated as viscous flow. When two fluid layers move relative to each other, a frictional force develops between these two layers which are due to the property of fluid called 'viscosity'. Boundary layer flows are the example viscous flow. Neglecting the viscosity effects in the fluid flow equation, the flow can be named as in-viscid flow.

2. Difference between Internal and External flow: 

The flow of an unbounded fluid over a surface is called ‘external flow’ and if the fluid is completely bounded by the surface, then it is called as ‘internal flow’. For example, flow over a flat plate is considered as external flow and flow through a pipe is internal flow.

3. Difference between Compressible and Incompressible flow: 

The flow is said to be ‘in-compressible’ if the density remains nearly constant throughout. When the density variation during a flow is more than 5% then it is treated as ‘compressible’. This corresponds to a flow Mach number of 0.3 at room temperature.

4. Difference between Laminar and Turbulent flow: 

The highly ordered fluid motion characterized by smooth layers of fluid is called ‘Laminar Flow’, e.g. flow of highly viscous fluids at low velocities. The fluid motion that typically occurs at high velocities is characterized by velocity fluctuations are called as ‘turbulent.’ The flow that alternates between being laminar & turbulent is called ‘transitional’. The dimensionless number i.e. Reynolds number is the key parameter that determines whether the flow is laminar or turbulent.

5. Difference between Steady and Unsteady flow: 

When there is no change in the fluid property at the point with time, then it implies as steady flow. However, the fluid property at a point can also vary with time which means the flow is unsteady/transient.

7. Difference between Natural and Forced flow: 

In a forced flow, the fluid is forced to flow over a surface by external means such as a pump or a fan. On the other hand, in a natural flow, density difference is the driving factor of the fluid flow. Here, the buoyancy plays an important role. For example, a warmer fluid rises in a container due to density difference.

6. Multidimensional flow:

 A flow field is best characterized by the velocity distribution, and thus can be treated as one-dimensional flow if velocity varies in only one direction. Similarly, two or three-dimensional flows can be defined.

Have you studied any other types of fluid flows that are not discussed in this article mention in the comments below.