How Streamline Flow Differs from Turbulent Flow in Everyday Situations
Streamline flow or a laminar flow is an uninterrupted flow (as of air) past a solid body in which the direction at every point remains unchanged with the passage of time.
Streamline flow is a type of flow of fluid which travels in regular paths. So, we can say that there is a smooth movement of layers of water passing from one end of the pipe to another. So, when you look at a stream flowing, you first observe a few things about it like the speed of the water in it, its width, amount of water flowing, etc. One of the primary things that characterize a stream is its flow which is also termed as streamflow. This page discusses the streamline flow, various applications explaining this concept in detail.
What is a Streamline Flow?
A liquid or fluid motion happens when shear stress acts on it. This shear stress or force is acting parallel to the surface of the liquid. In the case of a stream flowing, the gravitational force of the earth is acting upon it and pulling it down.
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Streamflow is described by a single atom's path in a fluid and is of two types: streamline flow and turbulent flow. A flow that is steady, smooth, and predictable is called streamline flow. Sometimes the flow of a stream could be marked by chaotic changes that we call a turbulent flow. Let us learn about streamline flow definition and distinguish between streamline and turbulent flow in this article.
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Principle of Streamline Flow
A streamline flow is also called laminar flow, and in this flow, there are no major velocity fluctuations. A streamline is a path of imaginary particles within the fluid that are carried along with it. The streamlines are fixed in a steady flow, and fluid travels in a smooth and regular path. This means that the flow properties like velocity, pressure, etc. at each point remain constant. To define streamline flow, think of the laminar flow consisting of laminae or thin layers, all parallel to each other. In a streamline motion, these layers of water are flowing on top of each other at different speeds, and there is no mixing between layers.
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If you draw a tangent to the streamline at any point in space in a streamline flow, it will be aligned with the instantaneous velocity vector at that point. These streamlines cannot cross each other at any one instant in time. The fluid in contact with the surface is stationary, and the other layers are sliding over it.
Now, let us understand another type of flow, called the Turbulent flow. Also, we will understand the difference between Turbulent and Streamline flow.
What is Turbulent Flow?
A turbulent motion in a fluid is an irregular motion caused either by high velocities or abrupt changes in velocities. If you imagine a ball in a river stream, can you predict its direction of motion? It is probably not because water is splashing all around and the ball could go any which way every second. It is similar to the turbulent flow of fluids where there are random and unpredictable fluid particles' motions. In a turbulent flow, fluid is not passing in parallel layers, and there is a high level of lateral mixing and disruption between layers.
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The three main characteristics of a turbulent flow are:
Eddies
Recirculation
Apparent randomness
At any given point in the fluid which is undergoing turbulent flow, there is a continuous change in magnitude and the direction of flow. In our bodies, blood flow is generally streamline or laminar. But in certain high flow conditions, laminar flow can get disrupted and result in a turbulent flow. The flow in large arteries at the branch points are also turbulent flows.
The streamline flow vs turbulent flow table below sums up the difference between streamline and turbulent flow:
Distinguish Between Streamline Flow and Turbulent Flow
Reynold’s Number
Reynold’s number is a dimensionless number that has a vital role in predicting patterns in a fluid’s behaviour. Reynold’s number is represented as Re, and it is used to determine whether fluid has a laminar or turbulent flow. Re is the ratio of forces of inertia (forces that tend to resist motion) to simple viscous forces (the intermolecular glue which holds the fluid together). At high values of Re, there is turbulence.
Re = inertial force/viscous force = (ρ * v * L)/𝜇
Where ρ is the density, v is the velocity, L is the diameter of the tube, and 𝜇 is viscosity.
It could also be expressed as:
Re = fluid & flow properties/fluid properties.
So if there is a glass of water in a jar at rest then flow properties are 0. Thus, the numerator in the above equation is 0, which means that fluid at rest is independent of Reynold’s number. When the jar is tilted, and water starts flowing, we can predict water flow using Reynold’s number.
FAQs on Streamline Flow in Physics: Definition & Key Concepts
1. What is streamline flow in physics?
Streamline flow, also known as steady or laminar flow, is a type of fluid motion where the fluid particles move along smooth, predictable paths called streamlines. In this flow, the velocity of every particle passing through a specific point in the fluid remains constant over time. The paths of different particles do not cross each other, resulting in an orderly, layered movement, much like a quiet, slow-moving river.
2. What are the key characteristics of streamline flow?
The primary characteristics of streamline flow are:
Constant Velocity: At any given point within the fluid, the velocity of each passing fluid particle is constant over time.
Non-Intersecting Paths: The paths of individual particles, called streamlines, never cross each other.
Orderly Motion: The fluid moves in smooth layers (laminae) that slide past one another without mixing.
Low Fluid Velocity: Streamline flow typically occurs when the fluid is moving at speeds below its critical velocity.
3. What is the main difference between streamline flow and turbulent flow?
The main difference lies in the nature of the fluid particle's path. In streamline flow, particles move in an orderly, predictable manner along smooth, parallel paths. In contrast, turbulent flow is chaotic and irregular, characterized by the formation of eddies and swirls. The velocity at any point in turbulent flow changes erratically. Streamline flow occurs at low speeds, while turbulent flow occurs when the fluid speed exceeds the critical velocity.
4. Can you provide some real-world examples of streamline flow?
Yes, here are some common examples of streamline flow:
The slow, gentle flow of water in a wide river or canal.
The smooth flow of air over the wings of an aeroplane, which is crucial for generating lift.
Thick liquids like honey or syrup pouring slowly from a container.
The flow of blood in the capillaries.
5. What is a streamline and what are its key properties?
A streamline is an imaginary line or curve drawn in a moving fluid such that the tangent to it at any point indicates the direction of the fluid velocity at that instant. Its key properties are:
The tangent at any point on the streamline gives the direction of instantaneous velocity of the fluid particle.
In a steady flow, the pattern of streamlines remains constant over time.
Two streamlines can never intersect, as this would imply a single fluid particle has two different velocities at the same point, which is physically impossible.
6. Are streamline flow and laminar flow the same thing?
While often used interchangeably in introductory physics, there is a subtle distinction. Laminar flow specifically describes a flow where fluid moves in distinct layers, or 'laminae', that slide smoothly over one another without mixing. Streamline flow is a broader term for any smooth, non-turbulent flow where fluid particle paths do not cross. All laminar flows are streamline flows, but one can conceptualise a streamline flow that isn't perfectly layered. For CBSE Class 11, they are generally treated as equivalent concepts.
7. How does the Equation of Continuity relate to streamline flow?
The Equation of Continuity (A₁v₁ = A₂v₂) is a direct consequence of the principle of conservation of mass applied to an incompressible fluid in streamline flow. It describes that the product of the cross-sectional area (A) and the fluid velocity (v) at any point along a pipe remains constant. This orderly relationship holds because, in streamline flow, the fluid does not accumulate or get lost at any point, ensuring a steady mass flow rate.
8. Why can't two streamlines ever cross each other?
Two streamlines cannot cross because the tangent to a streamline at any point gives the unique direction of the fluid's velocity at that point. If two streamlines were to intersect, it would mean that at the point of intersection, there are two different tangents. This would imply that the fluid particle located at that single point is moving in two distinct directions at the same time, a situation that is physically impossible.
9. Under what conditions does a fluid's flow transition from streamline to turbulent?
A fluid's flow remains streamline as long as its velocity is below a certain limiting value known as the critical velocity. When the fluid's speed exceeds this critical value, the orderly flow is disrupted and becomes chaotic, transitioning into turbulent flow. This transition point also depends on other factors like the fluid's viscosity and density, and the size of the conduit, which are collectively represented by the dimensionless Reynolds number.
10. How is Bernoulli's principle applied to fluids in streamline flow?
Bernoulli's principle is a statement of the conservation of energy for an ideal fluid undergoing streamline flow. It states that the sum of pressure energy, kinetic energy, and potential energy per unit volume remains constant along a streamline. A key application is that for a horizontal flow, where the velocity of the fluid is high, its pressure is low, and vice versa. This principle is fundamental to understanding aerodynamic lift and the operation of devices like venturi meters and atomisers.
11. Why is the concept of an 'ideal fluid' important when studying streamline flow?
The concept of an 'ideal fluid' is a theoretical model used to simplify complex fluid dynamics calculations. An ideal fluid is assumed to be perfectly incompressible (density is constant) and non-viscous (has no internal friction). Foundational principles like Bernoulli's theorem are derived under these assumptions because they make the analysis manageable. While no real fluid is truly ideal, this model provides an excellent approximation for many real-world situations, especially for fluids with low viscosity like air and water in streamline flow.
