Streamline flow

Introduction

Fluid is described as a substance that can alter shape in response to an external force. When a fluid is subjected to an external force, it begins to flow. Fluid dynamics is the study of fluids in motion. Have you ever seen a brook running beneath the bridge? What is the first thing that springs to mind when you see a streamline? The answer is the most typical characteristics of the stream, such as speed, width, and amount of water flowing. One of the most significant aspects of every fluid is its flow. The location or source of a stream is an important component in determining how much water flows through it. The source site of the stream has the potential to change both the speed and direction of flow within the stream.

When a steady flow of ink is introduced, the ink flows without mixing with the other layers of water, but when the flow is turbulent, the ink layer mixes with the other layers of water, as illustrated in the image below. The first type of flow is known as a streamline or laminar flow.

Water flowing from a tap has a smooth appearance when the flow rate is low, but as the flow rate increases, voids and disturbances may be recognised after reaching a certain threshold. In such a circumstance, introducing a stream of ink when the flow is smooth causes the ink to flow without mixing with the other layers, whereas introducing it when the flow is turbulent causes the ink layer to mix with the other layers of water, as shown in the image below.

This part will tell us about the first type, which is the streamline or laminar flow.

Definition of streamline flow 

Streamline flow in fluids is defined as the flow of fluids in parallel layers such that there is no disruption or intermixing of the layers and the velocity of each fluid particle passing by remains constant with time at a given position. There are no turbulent velocity variations here at low fluid velocities, and the fluid tends to flow without lateral mixing. The fluid particles move in a specific order with regard to the particles traveling in a straight line parallel to the pipe wall, so that the neighboring layers slide past each other like playing cards.

What do you understand from Streamlines?

Streamlines are defined as the paths traveled by fluid particles in steady flow conditions. If the flow lines are represented as curves, the tangent at any point on the curve gives the direction of the fluid velocity at that point.

The curves show how the fluid particles move in relation to time. The curve represents a map of the flow of this specific fluid, as well as a steady flow. This map is time-stationary, which means that every particle that passes through a spot behaves precisely like the particle that came before it.

In a laminar flow, the streamlines obey the continuity equation, i.e., Av = constant, where A is the cross-sectional area of the fluid flow and v is the velocity of the fluid at that location. Av is defined as the fluid’s volume flux or flow rate, which remains constant in steady flow. The velocity of the liquid decreases as the area of the cross-section increases, and vice versa.

Turbulent flow 

A turbulent motion in a fluid is defined as an irregular motion generated by either high velocity or sudden changes in velocities. Can you anticipate the direction of motion of a ball in a river stream? It’s unlikely because there’s water everywhere around and the ball could go in any direction at any time. It is analogous to the turbulent flow of fluids, in which the motions of the fluid particles are random and unexpected. Fluid does not pass in parallel layers in a turbulent flow, and there is a significant level of lateral mixing and disruption between layers.

A turbulent flow has three key characteristics:

• Eddies

• Recirculation

• The appearance of unpredictability

There is a continual change in amplitude and direction of flow at any given place in the fluid that is undergoing turbulent flow. Blood flow in our bodies is often streamline or laminar. However, in high flow circumstances, laminar flow can be interrupted, resulting in turbulent flow. At the branch points of big arteries, the flow is also turbulent.

Difference  between Streamline Flow and Turbulent Flow

Reynold’s number

Reynold’s number is a dimensionless number that plays an important role in forecasting patterns in the behavior of a fluid. Reynold’s number (Re) is used to evaluate if a fluid has a laminar or turbulent flow. Re denotes the ratio of inertial forces (forces that tend to resist motion) to simple viscous forces (the intermolecular glue which holds the fluid together). There is turbulence at high Re values.

Conclusion 

Therefore a  streamline flow, which is also known as a laminar flow, is one that has no turbulent velocity changes. As a result, the sole agitation of the fluid particles takes place at the molecular level. The fluid flow can be represented in this situation by a streamline pattern established within an Eulerian description of the flow field. These streamlines are designed in such a way that the tangent to the streamline at any place in space is aligned with the instantaneous velocity vector at that position at any point in time. This streamline pattern is identical to the flow-lines or path-lines that characterize the route of the fluid particles within a Lagrangian description of the flow field in a steady flow, but not in an unsteady flow.