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- เผยแพร่เมื่อ 1 ส.ค. 2024
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In this video, we’ll explain the basic principles of CFD or computational fluid dynamics.
Modeling involves the continuous mathematical functions that you use to describe the real flow. In reality, that flow is the result of many different laws of physics working together. To limit computational effort, it’s a matter of selecting only the ones that have a substantial impact on your flow topic: if you’re calculating the aerodynamic force on a wing, for example, there’s little use in taking the gravitational pull of the moon into account, as the effect is negligible. So, defining correct & relevant models is important to limit the modeling errors:
In case of fluid mechanics, the most important model is a set of partial differential equations called the “Navier Stokes” equations. These basically apply the laws of Newton for every small bit of the fluid, stating the dynamic balance between the forces acting on it and the change in its momentum. This conservation of momentum, together with the conservation of mass, allows you to describe the flow field.
For some very simple cases, like laminar flow through a pipe, there are analytical solutions: the entire flow field can be described using continuous mathematical functions. These allow you to calculate the exact velocity & pressure for any given location in the flow field at an infinite resolution.
But for anything more complex than these very simple cases, we don’t have such an analytical solution. That means we need to break down reality into small blocks for which we do have a solution. These blocks can be finite elements or finite volumes, also called cells. Think of it as the difference between analog and digital photography, where a complex image is described by simple pixels, each having just one color.
This process of breaking down a large continuous flow field into small cells is called meshing. For each of these cells, we can approximate the continuous Navier-Stokes equations by discrete algebraic equations. These allow us to calculate the pressure & velocity at the center of each cell, which is called the node, based on the values of velocity & pressure of the surrounding nodes.
The higher the order of these discrete approximations, the more surrounding nodes are included. This “reach” is called the computational molecule, resulting in a set of algebraic equations for each node. As the value of one node depends on the value of neighboring nodes and vice versa, the equations are connected. This means you need to solve them simultaneously by putting them together in a big matrix.
But before we discuss how to solve this matrix, we need to talk about the discretization error: “The difference between the exact solution of the governing equations and the exact solution of the discrete approximation”. The more cells you apply, the smaller this error. But this also increases the number of equations you need to solve, and with meshes typically containing millions of cells, this quickly becomes very expensive. So you’re best off applying small cells to locations where the flow is complex, and large cells where the flow is less curvy, typically further away from the object.
Once you have defined your mesh and your matrix of equations, it’s time to solve them. It’s possible to find the exact solution of this matrix problem through a direct method like Gauss elimination or LU decomposition. But this is very costly in terms of computational power and why bother solving the equations down to computer accuracy level, when your discretization error is much bigger anyway?
This is where faster iterative methods come in: they start by “guessing” an initial solution, which could even just be a standstill flow field, or “zero velocity” for every point. Then they linearize the equations around that point and improve the solution through iteration. If you iterate long enough, the flow field will converge to a stable solution, reducing the iteration error. The difference between this solution and the direct solution of the equations is called the iteration error.
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The AirShaper videos cover the basics of aerodynamics (aerodynamic drag, drag & lift coefficients, boundary layer theory, flow separation, reynolds number...), simulation aspects (computational fluid dynamics, CFD meshing, ...) and aerodynamic testing (wind tunnel testing, flow visualization, ...).
We then use those basics to explain the aerodynamics of (race) cars (aerodynamic efficiency of electric vehicles, aerodynamic drag, downforce, aero maps, formula one aerodynamics, ...), drones and airplanes (propellers, airfoils, electric aviation, eVTOLS, ...), motorcycles (wind buffeting, motogp aerodynamics, ...) and more!
For more information, visit www.airshaper.com - วิทยาศาสตร์และเทคโนโลยี
Are you running CFD simulations yourself? Feel free to share your experiences in the comments - Which software do you use, what do you like about it, what applications to do study, ...?
Hi! Yes, we've developed the entire platform around OpenFOAM - see www.airshaper.com/courses if you want to learn more about running OpenFOAM. One feature in particular is that we do all the meshing automatically for you, even if your 3D CAD model is not watertight! Feel free to check out this video: th-cam.com/video/12xA80foGXk/w-d-xo.html
Unfortunately, I wouldn't know how to help you on Ansys meshing - I haven't worked with that before.
Does openFOAM use an adaptive mesh?
@@wyattb3138 OpenFOAM features mesh refinement tools, but not a full "adaptive mesh refinement" algorithm out of the box. But it can be done - at AirShaper (www.airshaper.com) we have created a layer on top of OpenFOAM that will refine the mesh during the simulation based on intermediate results!
This is one of the best introductions to CFD on TH-cam - thanks for putting this out.
Thanks a lot Shaunak! I hope you find the other videos in our channel equally interesting 🙂
Yeahh, thebest vid i watched
true!!!!!
Can't be any better explanation with this simplicity. Hats off!
Thank you very much Shawon!
Saving this one for my university course 1,5 years from now. Nicely explained.
Ah, good luck with the university course then!!
Thank you so much. You have no idea how good you are and how clearly you have explained. The best introduction ever
Thank you VERY MUCH for the compliment Bhawana - I much appreciate it!
I still wonder why this video hasn't got more than a million views. This video, in any engineer's opinion, is the most important, crucial and essential video. Anyways, I love all your videos. I am working on modeling a personal F1 design and if all goes well, I will try to run those aero simulations in both openFoam and solidworks and would love to share with you soon hopefully.
We would indeed be very happy to see more views - we just haven't figured out how to achieve that. Do you perhaps know anyone with skills in that domain? I'm looking forward to see your design and CFD results!!
@@AirShaper Well I don't know anyone specific but there are a lot of famous youtubers you can view to check out the way they present their ideas. One specific guy I like is @chrisFix , who shares great DIY car videos down to the great details.
And of course, I will share my design and simulations once they are complete. Looking forward to it.
@@TheOnlyRaceEngineer ok thanks, I'll look into @chrisFix's channel!!
Very nicely and simply explained, cheers
Beautiful explanation. Better than all my lecturers combined. I have subscribed.
Thanks a lot Justice!! I hope you'll like our other videos as well :) Talk soon!
Many thanks 🙏🏼 for this great explanation for the CFD
I really appreciate your effort
Thank you 🤗
You're very Welcome Osama Ahmad! I hope it helps to to embark on a cool journey involving CFD :)
Crisp and clear👌 Kudos to the effort👍
Thanks Jake!
awesome and concise explanation from start to finish. great video
Thanks Daniyal, I'm really happy to get such nice feedback! I hope you're on a great track to enjoy CFD :)
What a crystal clear explanation i like the way you teach calm &pleasant. Plz make more videos on cfd
Thank you very much for those kind words Harshith, I much appreciate it! If you want, we also have some free course material at www.airshaper.com/courses --> old stuff, but perhaps still useful to learn OpenFOAM?
This is very well explained!
Thanks a lot Julio!
You are a saver. Thank you !
Great explanation!
Thanks Dani!
Great teacher. Thanks.
Thanks David!
I hope I have collected much to save from my exam today. Thanks.
Good luck with the exam, Tharanga!
Very nicely explained
Thanks Aman!
@AurShaper Amazing explanation! I am using ANSYS workbench for aerodynamic analysis. I am having problems with meshing. Could you create a video on how to solve meshing errors in ANSYS meshing? Thank you.
Hi Dr. Wouter, I will like to learn more about CFD and use it for my project work in school. I'm Bright from Ghana. Thank you for the nice introduction.
I'm glad the video has helped you to learn CFD!!
Excellent Explanation...
Thank you very much!
nice work. I was having some problems but it all clears now
I'm glad the video made things clear for you!
this discipline is just epic
We totally agree :D
all of this applies to computational electromagnetics as well. except there we are pretty confident that our models, which have been promoted to laws, are correct (at least in vacuum, where we don’t need to model materials...)
Hi Paul, that's interesting - I didn't know the accuracy was so much higher for electromagnetic field simulations!
Very nice
Thanks Emeka!
Hi, Do you know about Computational Fluid Dynamics (Continuum Mechanics) especially related to motion of bodies submerged in fluids. Basically i am having hard time even visualizing and starting to think about following problem:
Consider a rigid body (with a mass "M" and inertia tensor "I") which is completely submerged in a Fluid of constant viscosity "v" and constant density "d" at rest in a container (Boundary value problem).
Now consider the fluid is disturbed by some external force "F" at a point "P" inside the container.
How to calculate how much of the original force "F" acted upon that RigidBody and what are the components of that force on that rigid body.
Can you help ? Thanks.
I've seen some interesting tutorials on this in OpenFOAM, perhaps you can search for those?
If you want, we have some old course material available for free at www.airshaper.com/courses
Good luck!
What is the best free CFD software to start with? Which one will be applicable for Aerospace students?
I would recommend xfoil / xflr5 for aerospace students to get started as well as OpenFOAM. You can find some old course material here - www.airshaper.com/courses
nice and easy intro to CFDs at breakfast - really well explained
Thanks a lot Stephen!
I need to find a rear wing for my 2012 Nissan 370Z that has been CFD tested. Anyone have recommendations?
This one looks to be analyzed in CFD: www.aerodesign.com.au/wings/
Sir, I have a project on CFD modelling of desilting chamber.
So I want ask that which software is good for CFD modelling.
There are countless options: StarCCM, Ansys, ...
But if you're looking for an open source option, then I'd certainly recommend OpenFOAM
@@AirShaper thankyou sir.
Hey! I'm an undergraduate student and enthusiastic to learn about CFD analysis. Can you tell me if I can do an analysis for drag in Solidworks?
Solidworks indeed has a cfd module, but I'm not sure if it's included in your license. I don't know if it's still the case, but the CFD in solidworks used to be FloEFD of Mentor Graphics (now owned by Siemens).
Maybe you can check with IT of your department if you can get the CFD module? If yes, then you can indeed run a drag analysis.
@@AirShaper thank you for the reply! And what if I want to run it in Ansys?
And also, if I want to run a simple analysis of a model, what tests will be good enough?
Ansys is definitely good enough too. It's more a matter of setting all the parameters right. You'll find a lot of resources on www.cfd-online.com for specific case setups!
Thanks for all the help ❤️ And keep uploading good works like this. There's a lot to learn from you.
Why is pressure and velocity important in every cfd simulation?
Hi Tom, pressure and velocity are what define the flow field and thus all the resulting forces, moments, noise, vibrations, ...
He looks like Jake Gyllenhaal. Also, good video.
Good news, I have a plan B in case AirShaper doesn't work out :):) Glad you liked the video!
An actual example would have been better.
This explanation does not suffice.
Dear Aldo,
we chose to focus on the theoretical aspects in this video.
For practical examples (on Porsches, drones, motorbikes, ...) please do check out the other videos on our channel!
th-cam.com/users/airshaper
Or visit our blog at www.airshaper.com/blog for more practical examples.
Hope it helps!
@@AirShaper i understand. I am providing feedback from my point of view.