1.2.3 - Setting up Governing Equations
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Introduction to Governing Equations
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Today, we're going to dive into the governing equations in CFD. Can anyone tell me what governing equations are based on?
Are they based on the laws of physics?
Exactly! They are derived from the conservation laws of mass, momentum, and energy. Letβs remember these with the acronym 'M, M, E' β Mass, Momentum, Energy.
Why are these equations important?
Great question! They are crucial because they describe the behavior of fluid flows and heat transfer, providing the framework for CFD analyses.
So, do these equations apply to every fluid system?
Yes, they are adaptable to various systems, but the forms of the equations might change based on the complexity of the system. Let's summarize: governing equations are essential to CFD as they come from conservation laws.
Discretization of the Domain
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Next, we need to discuss discretization. Who can explain what it involves?
Isn't it about breaking the physical domain into smaller cells?
Exactly! This process is vital for applying numerical methods. We use methods such as finite difference, finite volume, or finite element to do this. Let's remember 'DVM' β Discretization, Volume, Method.
What is the purpose of discretization?
Discretization allows us to convert governing partial differential equations into algebraic equations that can be solved numerically.
Does this make the calculations easier?
Absolutely! By transforming these equations, we can handle complex fluid dynamics simulations more effectively.
Setting up Conservation Equations
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Once we discretize, the next step is setting up conservation equations for each cell. Why do you think this step is crucial?
Itβs so that we can capture the physics accurately for every part of the domain?
Correct! By formulating mass, momentum, and energy equations for each cell, we ensure each small region reflects the fluid and thermal behavior accurately. Letβs remember 'M, M, E' for mass, momentum, and energy conservation in each cell.
What happens if we don't set them up correctly?
If the equations are not accurately set, the numerical solution can be unstable or incorrect, leading to unreliable predictions β which we definitely want to avoid!
Introduction & Overview
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Quick Overview
Standard
In this section, we focus on the establishment of governing equations that are fundamental to Computational Fluid Dynamics (CFD). Key conservation laws of mass, momentum, and energy are highlighted, emphasizing their importance in determining flow behavior and thermal characteristics in fluid systems.
Detailed
In Computational Fluid Dynamics (CFD), governing equations are pivotal as they form the mathematical backbone for simulating fluid flows and heat transfer. The primary equations stem from the conservation laws of physics, specifically focusing on mass (continuity equation), momentum (Navier-Stokes equations), and energy (first law of thermodynamics).
This section delves into the core steps necessary for setting up these governing equations in CFD analyses. Initially, the physical domain must be defined followed by discretization where the domain is divided into small elements or cells through techniques like finite difference, finite volume, or finite element methods.
The formulation of appropriate conservation equations for each cell is crucial. Each of these equations captures essential physical phenomena that dictate the flow and heat transfer processes occurring in the system. This section discusses the significance of carefully setting up governing equations to ensure accurate and stable numerical solutions, which are then solved iteratively. By laying this foundational knowledge, we prepare students for more advanced topics like boundary conditions, numerical solutions, and post-processing results in the realm of CFD.
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Formulating Conservation Equations
Chapter 1 of 2
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Chapter Content
The appropriate conservation equations (mass, momentum, energy) are formulated for each cell.
Detailed Explanation
In Computational Fluid Dynamics (CFD), the first step in setting up governing equations involves formulating the conservation laws for each small volume or cell within the computational domain. These laws are based on the principles of physics which ensure that mass, momentum, and energy are conserved in any fluid flow problem. For each cell, the relevant equations are determined based on the flow conditions and physical properties of the fluid.
Examples & Analogies
Think of formulating conservation equations like creating a recipe for a dish. Just as you need to understand the quantities and types of ingredients required for your dish, in CFD, you must recognize the correct equations that represent quantities like mass and energy for each small 'cell' of fluid. If you skip an ingredient or miscalculate the amounts, the final dish will not turn out right, just like how inaccurate equations can lead to wrong simulation results.
Understanding Conservation Laws
Chapter 2 of 2
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Chapter Content
The governing equations are the conservation laws of physics: mass (continuity equation), momentum (Navier-Stokes equations), and energy (first law of thermodynamics).
Detailed Explanation
The governing equations in CFD are derived from the fundamental conservation laws. The mass conservation is represented by the continuity equation, which ensures that the amount of fluid entering a control volume equals the amount leaving it. The Navier-Stokes equations represent momentum conservation and account for fluid motion, forces, and viscous effects. Lastly, energy conservation is captured through the first law of thermodynamics, ensuring that energy is neither created nor destroyed in the process. Understanding these laws is crucial as they form the foundation of how fluid flows and heat transfer is modeled in simulations.
Examples & Analogies
Imagine a water system where water flows into and out of a tank. The amount of water inside at any time must reflect both the inflow (mass) and outflow (mass) accurately. If you were to ignore any inflow or outflow in your calculations, you would either overestimate or underestimate how full the tank is. Similarly, in CFD, neglecting the conservation laws can lead to incorrect predictions of fluid behavior, just as ignoring the water levels can affect your understanding of the water system.
Key Concepts
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Governing Equations: Mathematical models representing the conservation of mass, momentum, and energy.
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Discretization: The method of dividing the computational domain into smaller elements for analysis.
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Conservation Laws: Fundamental principles ensuring energy, mass, and momentum are conserved in fluid dynamics.
Examples & Applications
Example of governing equations includes the continuity equation for mass conservation, Navier-Stokes equations for momentum conservation, and the energy equation derived from the first law of thermodynamics.
In a heat exchanger simulation, governing equations help predict temperatures and fluid velocities across various sections, ensuring proper design and efficiency.
Memory Aids
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Rhymes
In fluid flows, remember βM, M, E,β / Conservation laws are the key!
Memory Tools
For governing equations, remember βM, M, Eβ to keep them all in line: Mass, Momentum, Energy!
Stories
Once upon a time, in a land of fluids, a wise ruler taught his subjects about mass, momentum, and energy. They learned to conserve these treasures in every simulation they created.
Acronyms
Use 'DVM' to recall
Discretization
Volume and Method β all vital for fluid analysis!
Flash Cards
Glossary
- Governance Equations
Mathematical equations that describe the conservation of mass, momentum, and energy in fluid systems.
- Discretization
The process of subdividing the physical domain into smaller, manageable elements or cells for numerical analysis.
- Conservation Laws
Fundamental physical laws stating that certain properties (mass, momentum, energy) remain constant in a closed system.
- Numerical Methods
Techniques used to solve mathematical equations numerically, particularly in CFD to simulate physical phenomena.
- NavierStokes Equations
Set of equations that describe the motion of fluid substances, essential for modeling fluid dynamics.
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