17.3.2 - Eddy Formation
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Introduction to Eddy Formation
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Today we'll talk about how eddies form in turbulent flows. Can anyone define what turbulence is?
Isn't turbulence the chaotic movement of fluid?
Exactly! Turbulence involves irregular fluctuations and mixing. Now, how do we visualize this?
Using virtual fluid balls? Like imagining balls of different sizes and colors?
Right! We can think of these virtual fluid balls disintegrating and integrating in turbulent zones. Can someone summarize how they behave?
In high turbulence, they disintegrate into smaller balls and form eddies!
Great! Remember, increased turbulence leads to more disintegration. Let’s move on to discuss Reynolds numbers.
So what are Reynolds numbers and why are they significant in distinguishing flow types?
They help determine whether flow is laminar or turbulent based on inertia and viscous forces.
Exactly! Below 2300 indicates laminar flow, above 4000 indicates turbulent flow. Can someone provide a summary of when transitions occur?
2300 is the critical value to transition from laminar to turbulent flow.
Correct! Understanding these transitions is crucial for designing efficient pipe systems.
Understanding Mass and Momentum Flux
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Now, let’s dive deeper into how turbulence affects mass and momentum flux. Can anyone explain what we mean by mass flux?
It’s the mass of fluid passing through a unit area over time, right?
Exactly! And in turbulent flow, these fluxes fluctuate significantly. Can someone visualize how these changes occur?
When these fluid balls disintegrate due to turbulence, they change their velocities, causing changes in mass flux.
Well done! And how do we relate this to momentum?
We can also see changes in momentum flux due to fluctuations in velocity.
That’s right! These effects are what we see in turbulent flows causing chaotic behaviors. How can we summarize the impact of turbulence on mass and momentum flux?
Turbulence leads to significant variations in both mass and momentum as fluid balls disintegrate and their velocities change.
Perfect summary! Remember, these concepts are essential for understanding the dynamics in fluid transportation systems.
Introduction & Overview
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Quick Overview
Standard
Eddy formation is a key phenomenon in fluid mechanics, particularly in turbulent flow. The section discusses how virtual fluid balls disintegrate and integrate in turbulent conditions, leading to momentum and mass flux changes. It also elaborates on the transition between laminar and turbulent flow characterized by Reynolds numbers.
Detailed
Eddy Formation
This section discusses the concept of eddy formation in turbulent flows. As fluid flows, particularly in high Reynolds number scenarios, it undergoes various states, transitioning from laminar to turbulent flow. This transition is marked by the disintegration and integration of virtual fluid balls, leading to the formation of eddies. When the fluid experiences turbulence, it can be visualized as a series of colored balls that disintegrate and swirl together, creating smaller balls or clusters that move at different velocities.
Key concepts include:
- Virtual Fluid Balls: A model to help visualize how fluid particles interact during turbulence.
- Transition Between Flows: The critical Reynolds number indicates the transition between laminar flow (Re < 2300), transition flow (2300 < Re < 4000), and turbulent flow (Re > 4000).
- Mass and Momentum Flux: The section explains how fluctuating velocities in turbulent flow lead to significant changes in both mass and momentum flux, resulting in chaotic fluid behaviors. Overall, understanding eddy formation is crucial for designing efficient pipe systems for fluid transport.
Youtube Videos
![[CFD] Eddy Viscosity Models for RANS and LES](https://img.youtube.com/vi/SVYXNICeNWA/mqdefault.jpg)
![[CFD] The k - epsilon Turbulence Model](https://img.youtube.com/vi/fOB91zQ7HJU/mqdefault.jpg)
![[CFD] Large Eddy Simulation (LES) 2: Turbulent Kinetic Energy](https://img.youtube.com/vi/QKDFTCUh7zU/mqdefault.jpg)
![[CFD] Large Eddy Simulation (LES): An Introduction](https://img.youtube.com/vi/r5vP45_6fB4/mqdefault.jpg)
![[CFD] Large Eddy Simulation (LES) 3: Sub-Grid Modelling](https://img.youtube.com/vi/N81Io_yrOQU/mqdefault.jpg)
Audio Book
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Understanding Turbulence with Virtual Fluid Balls
Chapter 1 of 4
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Chapter Content
Let me repeat that things that we knew how the turbulent zones the flow what is going in this ball start disintegrating it. That means, the balls become the smaller number of balls will be there and as they have the smaller balls, there will be a mass actions, the momentum actions at different axis.
Detailed Explanation
In turbulent flow, the fluid behaves in an unpredictable manner, leading to the disintegration of larger fluid 'balls' into smaller ones. As a result, these smaller balls generate changes in mass and momentum, which is essential for understanding turbulence. The larger balls represent larger mass flows, while the smaller ones represent more chaotic motions caused by turbulence.
Examples & Analogies
Imagine a large clump of cotton being tossed into a windy environment. Initially, the cotton is a solid mass, similar to a large ball of fluid. However, the wind (representing turbulence) breaks the cotton apart into smaller fibers that scatter in various directions. Just as the small fibers carry different amounts of mass and energy, the smaller fluid balls in turbulent flow behave similarly.
Eddy Formation in Turbulent Flow
Chapter 2 of 4
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Chapter Content
If I conceptually that I have 100 number of balls or more than 100 number of balls, the same things happen. There is disintegrations. As the disintegrations has happens it this thus a cluster of the smaller balls, they can make a small vertices which we call eddies.
Detailed Explanation
When many fluid balls disintegrate due to turbulence, they can group together to form vortices known as eddies. These eddies are swirling motions in the fluid that can enhance transport processes (like mixing) and energy dissipation. Understanding how eddies form and evolve helps in analyzing turbulent flows.
Examples & Analogies
Think of a whirlpool in water as an example of eddy formation. When water flows at high speed into a small area, it can swirl around, forming a vortex. This swirling water represents the clusters of smaller balls forming eddies in turbulent flow, illustrating how energy and mass are mixed and dispersed in fluids.
The Role of Eddies in Energy Dissipation
Chapter 3 of 4
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Chapter Content
So when you have the turbulent flow, your energy dissipations, the mass flux computations, the momentum flux computations because of the fluctuating velocity components we are getting additional terms.
Detailed Explanation
In turbulent flows, eddies play a critical role in how energy is dissipated within the fluid. As these eddies form and interact, they can transfer energy from larger scales to smaller scales, where it is finally dissipated as heat due to viscous forces. This understanding is crucial in the design and analysis of systems involving fluid flow, such as pipelines or natural water bodies.
Examples & Analogies
Consider a blender mixing ingredients. The blades create small vortices (eddies) that mix the ingredients together efficiently, while the energy from the blades transforms into heat, leading to a homogeneous mixture. Similarly, in turbulent flow, energy dissipates through the continuous interaction of eddies.
Measuring Effects of Turbulence
Chapter 4 of 4
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Chapter Content
When you come to turbulent flow do not show only u, v, w. You should show three components. That is fluctuating velocity components, which varies instantly at that measurement locations and you have a time average velocity component.
Detailed Explanation
In turbulent flows, one must consider both the average velocity and the instantaneous fluctuations of the velocity components in three dimensions: x, y, and z. The average gives an overall sense of flow behavior, while fluctuations indicate the chaotic nature inherent to turbulence. Measuring both ensures an accurate representation of the flow.
Examples & Analogies
Think about a crowded room filled with people. The general trend of movement (like walking towards an exit) represents the average velocity, while the small jostling and sudden changes in direction among individuals showcase the fluctuating components. Observing both aspects helps understand the overall dynamics of the crowd, just like measuring both average and fluctuating velocities in turbulent flows helps comprehend fluid movement.
Key Concepts
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Eddy Formation: The process by which fluid motion becomes chaotic and forms circular eddies.
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Reynolds Number: A measure that helps assess whether a flow will be laminar or turbulent based on flow conditions.
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Mass Flux: Vital in analyzing how fluids move through systems; changes significantly in turbulent flow.
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Momentum Flux: Demonstrates the effects of turbulence on fluid motion, crucial for understanding dynamics.
Examples & Applications
A stream in nature that flows smoothly can be considered laminar flow, whereas water falling over a waterfall is a classic example of turbulent flow with eddy formation.
When mixing cream into coffee, the swirling motion creates eddies as the cream disperses, illustrating turbulent behavior.
Memory Aids
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Rhymes
Eddies swirl and twist around, in turbulent flows, they abound.
Stories
Imagine a colorful river where each drop of water forms a small ball. As they travel faster, they dance and swirl, making new paths through the turbulent current, creating eddies along the way.
Memory Tools
Remember R-League: R for Reynolds Number, L for Laminar, E for Eddies, A for Average Flow, G for Gravity, E for Equilibrium – think about how these concepts relate.
Acronyms
Use the acronym 'TEMP' to remember
for Turbulent
for Eddies
for Mass Flux
for Pressure drop in fluids.
Flash Cards
Glossary
- Eddy
A circular movement of fluid, often occurring in turbulent flow.
- Reynolds Number
A dimensionless number that helps predict flow patterns in different fluid flow situations.
- Virtual Fluid Balls
A conceptual model where fluid elements are represented as moving balls to visualize fluid behavior.
- Mass Flux
The mass of a substance that passes through a surface per unit time.
- Momentum Flux
The amount of momentum flowing through a unit area per unit time, relevant in fluid dynamics.
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