Streamline and Turbulent Flow

The resistance to motion that most fluids provide is referred to as viscosity. Whenever there is relative motion between layers of fluid, viscosity develops. It precisely quantifies the resistance to flow caused by internal friction between fluid layers as they pass through one another during fluid movement. 

Viscosity may also be defined as measuring a fluid’s thickness or barrier to passing items through it. Due to its strong intermolecular interactions, a liquid with a high viscosity resists motion by creating a lot of internal friction, which prevents layers from moving past one another. A fluid with low viscosity, on the other hand, flows readily because its molecular composition causes very little friction when it is in motion.

Now, the question is, what are streamline flow and turbulent flow?

Definition of streamline flow

A laminar flow, also known as a streamline flow, is a continuous flow (as of air) past a solid body in which the direction at each point remains constant over time. The term “streamline flow” refers to a fluid flow that follows a set of rules. So, from one end of the pipe to the other, there is a steady circulation of layers of water. When you see a stream, you initially notice a few factors, such as the speed of the water, the breadth of the stream, the volume of water flowing and so on. The flow of a stream, also known as streamflow, is one of the most important characteristics.

Definition of turbulent flow

In contrast to laminar flow, which flows in clean channels or layers, turbulent flow can be termed a form of fluid (liquid or gas) movement in which the contained fluid suffers random fluctuations and/or mixing. The fluid’s speed at a given position in a turbulent flow constantly changes in direction and magnitude. Even though the currents are mild, the movement of the river and the winds are often tumultuous in the same sense. While the water or the air eddies and swirls, most of it flows in a definite direction. 

Characteristics of streamline flow

There are no substantial velocity variations in a streamline flow, also known as laminar flow. A streamline is a trail of virtual particles transported together with the fluid. The streamlines are fixed in a steady flow and the fluid follows a smooth and consistent course. This indicates that the flow parameters at each site, such as velocity, pressure and so on, stay constant. 

Consider a laminar flow, which consists of laminae or thin layers parallel to one another. These layers of water flow at various speeds on top of one other in a streamlined motion and there is no mixing between them.

Characteristics of turbulent flow

A turbulent flow has three key characteristics:

• Eddies 
• Recirculation
• Randomness appears to exist.

There is a continual change in amplitude and direction of flow at any given place in a fluid that is undergoing turbulent flow. Blood flow in our bodies is typically streamlined or laminar. However, laminar flow can be interrupted under some high-flow situations, resulting in a turbulent flow. 

At the branch sites of big arteries, the flow is also turbulent. The uneven movement of the fluid’s particles characterises the flow. The average motion is in the flow’s direction. The flow velocity profile for turbulent flow is relatively flat in the pipe’s central portion and rapidly dips near the walls. 

Examples of streamline flow and turbulent flow

Stagnant rivers and canals exemplify laminar flow. The water in tranquil rivers or other bodies of water flows slowly and smoothly. The water body has no waves or swirls, implying that the distinct layers of water do not interfere and follow a straight route parallel to one another.

The blood in the arteries flows in a tumultuous manner. The aorta’s curvature causes the blood flow to bend, forcing the blood cells to mingle together. A turbulent flow develops as a result of this. A turbulent blood flow is often caused by a bulge in the arteries. The arterial wall is also subjected to increased radial pressure and shear stress as a result of this.

Conclusion

There is extensive use of streamline and turbulent flow such as pipes, ducts and heat exchangers are typical examples of industrial equipment that are designed to induce the desired flow regime (laminar or turbulent). 

Particles display extra transverse motion when the flow is turbulent. This increases the heat transfer by raising the rate of energy and momentum exchange between them. Turbulent flow is thus beneficial in situations where a relatively cold fluid is mixed with a warmer fluid to lower the warmer fluid’s temperature.