[CFD] Inflation Layers / Prism Layers in CFD

Рет қаралды 82,063

Күн бұрын

An introduction to inflation layers / prism layers, which can be generated by the majority of unstructured mesh generators (ICEM CFD, ANSA, ANSYS Workbench, SnappyHexMesh). The following topics are covered:
1) 02:00 Why do we use inflation layers in CFD?
2) 13:34 How do we choose the number of inflation layers (N) and the geometric growth ratio (G)?
3) 32:45 Why does the cell volume transition from the final layer to the freestream mesh need to be small?
#inflationLayers #fluidmechanics101 #meshing
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Check out the calculator on my website for calculating the growth ratio and the first layer height:
www.fluidmechanics101.com/pag...
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Some useful references
1. Computational Fluid Dynamics Blog - Leap Australia
'What y+ should I use? Part 3 - Understanding impact of y+ and the number of prism layers for flow resolution'
www.computationalfluiddynamic...
2. Wikipeda - Geometric Series
en.wikipedia.org/wiki/Geometr...
NOTE: the formula for the geometric series needs to extend from k=0 to N-1, not k=0 to N.
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Learn how to write your own CFD code in MATLAB and python (for intermediates):
dr-aidan-wimshurst-s-school.t...
Learn how I draw my figures and diagrams in Inkscape (for everyone):
dr-aidan-wimshurst-s-school.t...
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www.fluidmechanics101.com/pag...
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Disclaimer
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The methods, algorithms, equations, formulae, diagrams and explanations in this talk are for educational and demonstrative purposes only. They should never be used to analyse, design, accredit or validate real scientific / engineering / mathematical structures and flow systems. For such applications, appropriate trained, qualified and accredited (SQEP) engineers / scientists should be consulted along with the appropriate documentation, procedures and engineering standards. Furthermore, the information contained within this talk has not been verified, peer reviewed or checked in any way and is likely to contain several errors. It is therefore not appropriate to use this talk itself (or any of the algorithms, equations, formulae, diagrams and explanations contained within this talk) as an academic or technical reference. The reader should consult the original references and follow the verification and validation processes adopted by your company / institution when carrying out engineering calculations and analyses. Fluid Mechanics 101 and Dr. Aidan Wimshurst are not accountable or liable in any form for the use or misuse of the information contained in this talk beyond the specific educational and demonstrative purposes for which it was intended.

Пікірлер: 236

@lucaslincoln5712 2 жыл бұрын

Congratulations, excellent contribution! We can also consider a constraint on the size of the element of the last layer, to provide a smooth transition between the elements of the layer and the surrounding mesh. It is common to choose the average size of the surrounding mesh elements. For a 2D mesh with triangular elements, let's imagine that the area of the last element of the layer has to be approximately the area of the triangular element of the mesh just around the layer, so: Area of last layer element: A = (x1+x2)*y_last, where y_last = y*G^(N-1). Area of surrounding mesh element: A = (x1+x2)*h/2 Therefore: h=2*y*G^(N-1)=2*y*(G^N)/G (for square elements h = y*G^(N-1)). Substituting G^N into equation (13), and rearranging: G = (δ-y)/(δ - h/2) and, N = 1 + log(0.5*h/y)/log(G), in previous equation note that h/2 < δ. We round off the number of layers and recalculate the growth rate: G = (0.5*h/y)^(1/(N-1))

@fluidmechanics101 2 жыл бұрын

This is awesome. I'm going to pin the comment for everyone to see

@vigneshwaransankar1899 3 жыл бұрын

If you write a book I will be the first to buy a copy!

@EngLhag 3 жыл бұрын

I was revisiting this video and I have just realized that we don't actually need to use root-finding algorithm such as Newton-Raphson to solve equation (13) shown at 28:40. We can rearrange that equation and then apply logarithm to both sides, ending with: N = Ln (CG-C+1) / Ln (G). With C = delta_99 / y_H Common values for G are 1.1 or 1.2 (which is in the range you presented in the slides), so the solution is straight forward. Btw I have already implemented this new equation to my Excel sheet.

@fluidmechanics101 3 жыл бұрын

Well spotted! I spent ages trying to rearrange it into a closed form solution 😄 I have pinned your comment so everyone else can see as well

@skep2825 3 жыл бұрын

Really enjoyed that, super interesting - as per normal! And yes, would love to see more on meshing

@mohammedziou 3 жыл бұрын

Just by the time I started learning CFD you started to add content that i had questions about. Thank you :)

@alfamaniacGR 3 жыл бұрын

Solid work! Thanks a lot for sharing your knowledge with us! Cheers!

@Michallote 2 жыл бұрын

This is groundbreaking to me, I´m learning so much from you!

@sebastienricciardi883 3 жыл бұрын

Very useful, thank you. Looking forward to see other mesh related videos

@yuvrajjohri19 2 жыл бұрын

Really appreciate your efforts for putting this valuable knowledge online.

@dianedenonneville4259 2 жыл бұрын

Amazing video, I love your channel! As a high school student finding videos on fluid dynamics which are understandable is so hard, but this was perfect

@abrahakahsay Жыл бұрын

Dr. Aidan, you are a blessing. Thank you for your contributions.💙

@syedfaisalhussain6460 2 жыл бұрын

This video helped me to understand meshing better and concept of inflation layer covered in this video was what I was searching on youtube. Looking forward to learn more about CFD and fluid dynamics with your help.

@adibyahya1143 3 жыл бұрын

i really need this to complete my undergraduate project. thank you so much.

@interfluo6420 3 жыл бұрын

Absolutely amazing work, thank you!

@krysolet2003 3 жыл бұрын

Thank you! I would say this topic is essential. I looked at my meshes and it was immediately clear they need to be completely remeshed.

@teodorbabic8007 3 жыл бұрын

Great video, very very useful. I recently completed my Master's Degree in Aeronautical Engineering and my thesis was a CFD simulation of flow around thick airfoil. I was misunderstanding the process of mesh generation and now a lot seems more clear to me. Really great work, I hope you continue posting more and more videos and my answer to your question on whether you should continue videos on mesh generation - definitely !

@HassanKM2006 Жыл бұрын

It is very useful for me, and I really hope you can give more talks like this.

@Mohamed_Khalaf 5 ай бұрын

Thank you for the helpful in-depth explanation !❤ Your video was exactly what I needed to learn about inflation layers

@navathaalle2580 3 жыл бұрын

I have seen most of your videos and they are really very very helpful for CFD problem solving . So thank you very much for posting your videos . We would be more happy if you also post some videos on errors in CFD solvers and some more videos on the CFX or fluent software as well as how to solve errors which will not be straight forward at all . Hope to see them soon , thank you 🙏

@argcargv 3 жыл бұрын

Another problem with large volume transitions is that these volumes appear in the system matrix. Large volume transitions can result in much stiffer system matrices yielding poor iterative performance, and sometimes solver divergence.

@fluidmechanics101 3 жыл бұрын

I've pinned your comment, as this is another great point that was missed out 👍

@tejesdas3896 2 жыл бұрын

Brilliant presentation, absolutely. Thank you so much. I would like to see more videos on Ansys Fluent Meshing, especially on local sizing including & 3D visualization of unstructured meshing and grid optimization.

@christosvasiliou219 Жыл бұрын

dude, i love you so much, thank you for all of your amazing videos

@yuvrajjohri19 2 жыл бұрын

Wonderful video. Captured every detail.

@mattheushenriquemores5693 3 жыл бұрын

I totally agree with your opinion... There isn't too much information on how to to do a great mesh!!! Unhappilly I've found your content just now

@marcwerro6725 2 жыл бұрын

You are the MVP! I am working on my Bachelor Thesis and you are saving me from reading loads of dry and boring literature which I would struggle to understand. Thank you!

@apocalypt0723 3 жыл бұрын

Thank you so much. Would love to see more mesh related videos.

@maciejmarczak3853 3 жыл бұрын

Damn... Just started working on quite big project with approx. 150 layers on the airfoil profile. I think I will find this talk EXTREMELY USEFUL ;) thanks for well done job. Regards

@VascoBreitenfeld Жыл бұрын

Outstanding Video! thank you for making these!

@fulgencedione4775 3 жыл бұрын

Thanks for this interesting and helpful tutorial. I really enjoyed it.

@atifali3941 2 жыл бұрын

Amazing Lecture, most useful for an engineering student like myself. It would be much appreciated if further meshing methodolgy videos could be uploaded. Thank you once again and keep up the excellent content.

@vigneshsp4619 3 жыл бұрын

I really loved the talk, Thank you very much.

@omonua3890 2 жыл бұрын

I'm really fascinated with all of your videos. Big thanks! By the way, a topic "How should we do a mesh refinement study" would be very useful. In many research papers, authors do comparision base on the number of cells but not the meshing parameters

@rohitkshirsagar6639 3 жыл бұрын

Very good information.... Cleared lot of doubts in layer generation...

@vessela-b8871 5 ай бұрын

How I wish I knew this years ago! Great information as I do my PhD by the way! Thank you so much sir!

@35k67 3 жыл бұрын

I'm really looking forward on a video about Enhanced Wall Treatment in Fluent. Keep up the great work!

@Michallote 2 жыл бұрын

there is one already uploaded on his channel!

@khalilalani2707 2 жыл бұрын

Great video, very useful. Please keep on .

@shriharri1873 Жыл бұрын

Loved this work!!

@abdelrahmanmahdy9354 Жыл бұрын

It is quite useful! appreciate your work.

@francischewechikweto3987 7 ай бұрын

Excellent delivery

@willturner1635 Жыл бұрын

very informative, thank you for your expertise!

@sylwiajurczak4854 Жыл бұрын

Great video, thanks! This knowledge I needed :)

@blktayeb 2 жыл бұрын

thank you very much for your generosity in sharing this knowledge.

@mohammaddaliri7713 3 жыл бұрын

no matter what topic you go through, I like what you say

@jordanarmstrong273 2 жыл бұрын

Learnt some valuable info for my dissertation, thanks 👍

@corisco93 Жыл бұрын

This lecture is great!! thank you very much!!

@reflactor 2 жыл бұрын

This video was extremely helpful. Thank you. For anybody generating meshes with Pointwise, they use the term TRex instead of inflation layers, but it's the same idea. Also, to avoid the volume ratio problems, the inflation layers (TRex) grow until the cells/prisms reach isotropy. I'm looking forward to watching more of your videos. Keep up the great work!

@fluidmechanics101 2 жыл бұрын

Exactly! Thanks for your input 🙂

@ilhantalih9949 3 жыл бұрын

Thanks sir for great explanations and issues

@user-vk1oh9pq2e 3 жыл бұрын

Thanks for the informative video

@yvespousset 3 жыл бұрын

Very clear ! Without wall function

@jacklav1 2 жыл бұрын

Excellent talk

@AaronD-lv2ks 2 жыл бұрын

This is really really useful thanks for making this video!!!!

@mangy5885 Жыл бұрын

great one bro

@arminkashani5695 Жыл бұрын

Amazing video! Thanks.

@soufianeelmanssouri4841 Жыл бұрын

thank you so much you saved us a lot of time . the explication was so useful

@turalsuleymanov4529 Жыл бұрын

Amazing Job!

@EngLhag 3 жыл бұрын

Great job. Thanks for the video. I have my own excel file to calculate y+ and I guess I'll add these formulas to help me estimate my first guess for the inflation mesh =)

@fluidmechanics101 3 жыл бұрын

Awesome!

@mattheushenriquemores5693 3 жыл бұрын

Amazing Content!

@kirpahirom7209 3 жыл бұрын

you are just amazing sir

@davidwang8270 3 жыл бұрын

Very useful!

@sergniko 2 жыл бұрын

This is a really good talk

@HuyNguyen-fq4rh 3 жыл бұрын

Please consider put Star CCM+ on your CFD software list :)

@Samer-qd4gs 2 жыл бұрын

... I really appreciate ur work u have all my thanks 🙏🙏🙏🙏

@mo_lan1323 10 ай бұрын

so helpful, thank you soooo much 😘

@harshithrajamahanti7166 2 жыл бұрын

very useful thank you!

@is-ig4zh 3 жыл бұрын

Thank you so much sir!

@abhishektrivedi2255 2 жыл бұрын

Thank you!

@prashanth9316 10 күн бұрын

Thanks for your effort

@Sanoj_Yadav_ 5 ай бұрын

Thank you so much sir

@sundarrajann.c8844 3 жыл бұрын

Brilliant.. Thanks.!

@shorobalamakash2250 2 жыл бұрын

Thank you so much...

@jimeshpitroda937 2 жыл бұрын

Thank you

@ashutoshsingh-et7vm 3 жыл бұрын

hello Aiden sir Very nice video please make the next video on CFD of combustion

@samuelm9199 3 жыл бұрын

Great summary of the topic. I'd be interested in any suggestions for meshing with a stalled wing arise. I've read some allusions to meshes being to fine. In practice reducing element size in the x direction led to stall not being apparent from the simulation. I understand that no turbulence model properly predicts stall but any advice would be good. It seems like a nebulous topic like the inflation layers.

@corisco93 Жыл бұрын

Great video! I would like to let you know that there is another channel called "ANSYS TUTORIAL | ANSYS COURSE | SIMULATION " that has uploaded this video. The name of the video is "Ansys | Inflation Layers Prism Layers In CFD".

@fluidmechanics101 Жыл бұрын

Thanks for letting me know. I really appreciate it

@maciejmarczak3853 3 жыл бұрын

As I expected, it was super informative video and I would love to see more from Ypu about meshing strategy! Maybe I missed something, but why huge number of layers can impact resolution of the simulation? I thought that it can only unnecessary increasy the computation time. Again Thank You for the contribution Sir!

@fluidmechanics101 3 жыл бұрын

Ah sorry for the misunderstanding. Less layers can impact resolution. More layers increases computational time

@soroushasadian9100 Жыл бұрын

Perfect

@padla87 3 жыл бұрын

Some points I wanted to highlight: 1. If total thickness of your prismatic layers is greater then delta_99 then sudden cell volume increase shouldn't make any significant effect on friction coefficient, as friction is mostly generated in boundary layer. 2. In internal flows boundary layer usually spreads across the whole cross-section of a channel. So following your recommendations, meshes for internal flows should consist only of prism layers...

@fluidmechanics101 3 жыл бұрын

Yes to both. For 2) you normally have to have a few unstructured cells near the middle of the pipe to finish the mesh off (have a look for butterfly meshes, these are pretty popular for pipes)

@leoha88 Жыл бұрын

Thank you for a nice explanation. Finally, I got a better understanding on defining a Y+. But, how to estimate Y+ for a complex geometry where flow accelerates/decelerates and defining dimension varies?

@fluidmechanics101 Жыл бұрын

Just use your best guess. What is a representative length? How fast is the flow (roughly)? The important thing is to get the order of magnitude, not the actual value

@EngineersFirelli 3 ай бұрын

Hello Dr. Aidan, Thanks a lot for all your videos, which my colleagues and I find extremely useful! Thank you for all the time and effort you are investing in it, for the high-quality material you are producing and the clear explanations!! I have two questions regarding the topic of inflation layers: 1. When you say in pipe flow it is common practice to size the prism layers to cover 20% of the diameter, is this the height of the actual prism layer on the inner pipe wall? (which would give 40% of the diameter of the pipe covered by inflation layers if we take the layer on the opposite side, along the diameter) Or is it 20% in total, which means 10% on each "side" (10% of the diameter is the actual thickness of the prism layer) 2. In the Inflation Layer Calculator on your website (and also in the course video), I am a bit confused about the term "maximum growth ratio" : if I understand correctly, that value of G is actually calculated from the equation $ \delta_{99} = y_H \frac{1-G^N}{1-G} $. This is the value that allows the total height of the prism layers to match exactly the estimated boundary layer thickness $\delta_{99}$, with a given number of layers N chosen by the user. If I take for G a value higher than the calculated value, then my boundary layer will SURELY be contained within the inflation layers (which was actually the objective). I know it will make the mesh unnecessarily large, but I'm just saying that the objective is still fulfilled. On the other side, if I take for G a value smaller than the calculated one, the condition is not fulfilled anymore. The prism layers will not contain the entire boundary layer. So, according to my understanding, if the objective is that the inflation layers contains the entire boundary layer, shouldn't the value we are calculating actually be called "Minimum Growth Ratio" ? Thanks a lot in advance, I really highly appreciate your work and your videos.

@EngineersFirelli 2 ай бұрын

For anyone who might have the same questions, here is the reply I received from Dr. Aidan: Hi Theo 1) It's been a long time since I wrote this video, but I'm guessing 20% means 10% on each wall. 2) I think the implication is that if you adopt a higher growth ratio than the calculated value then there would be fewer layers between the wall and the edge of the boundary layer. This would give poor accuracy. For example, if you took an extreme case and went with a growth ratio of 5, you might only have 2 or 3 layers between the wall and the boundary layer thickness. This would give a really inaccurate answer, so you should reduce G and add more layers. Kind regards Aidan

@christopherclement984 3 жыл бұрын

Hello really enjoy your CFD talk in your channel. can I ask to discuss a topic about the fundamental of 6-DoF. Thankyouu

@yobinbou2560 3 жыл бұрын

In case of the upstream flow condensation in a vertical duct, the inflation layer should cover both condensate film and boundary layer on the film surface? What would be the correct approach? Here I am talking not about the stable upstream flow where one would have stable falling film, but rather the case, where the flow velocity increases that much, that condensate begins to accumulate inside the pipe and liquid would be present across whole cross-section. Any comment would be useful. Thank you & great job with video lectures!

@fluidmechanics101 3 жыл бұрын

It sounds like you might need a pretty fine mesh resolution across your entire geometry, as you need accurate gradient calculation everywhere (you don't have a uniform freestream, which is usually assumed for boundary layer flow over a flat plate). For your case it sounds like a fully structured mesh in ICEM CFD or a hexcore mesh would be a good idea 👍

@abinkrishnan3210 Жыл бұрын

Thank you so much for the wonderful video. You are a great teacher. I have one question reagrding the calculation of growth ratio. Since the growth ratio G is above 1, shouldn't the formula in (6) be yH*(G^N-1)/(G-1)?

@dylanharris1601 2 ай бұрын

Does anyone know the previous video he is mentioning where he covered the y+ understanding? Thanks,

@rahulkrishnah4776 3 жыл бұрын

This video was really helpful. please do a video on mesh independent study using Richardson extrapolation technique

@fluidmechanics101 3 жыл бұрын

I go through Richardson extrapolation in a lot of detail in my course 'CFD for Professionals'. You can find it on Udemy or from my website. I think it is exactly what you are looking for 🙂

@rahulkrishnah4776 3 жыл бұрын

@@fluidmechanics101 i will look into that

@rahulkrishnah4776 3 жыл бұрын

@@fluidmechanics101 Hi Dr Aidan, Thanks for the reply to the earlier post and I have joined for your course in udemy. I have one more doubt. I tried y+ = 1 and generated mesh in Starccm+ as per your video. When I closely observe cells in the vicinity of wall, aspect ratios are getting destroyed to a greater extent as you said in video. So my doubt is, Is there any recommended range for aspect ratios especially for cells adjacent to wall.

@fluidmechanics101 3 жыл бұрын

I'm not sure about Star CCM but most CFD codes are happy if the aspect ratio is less than 2000. You can always just try running your case and see if it runs ok? If not then try reducing the aspect ratio until you are able to get a stable solution. You can then use this solution as an initial condition for a finer mesh 👍

@rohanverma4145 3 жыл бұрын

Thank you for making this video it clarify a lot of things for me. I have one question, to define the boundary layer thickness, we have to calculate Re and L, for a simple case of a flat plate, L is the length of the plate, and for pipe, its a hydraulic diameter. But in engineering application, the geometry is quite complex, if we take an example of formula 1 or engine cooling jacket, What value of L we should consider/ calculate?

@fluidmechanics101 3 жыл бұрын

The length of the car would probably be a good guess 👍 Remember that this is all to create a good initial mesh. After you have run your initial simulation it is worth looking at the mesh and checking to see if it is any good. (I.e check y+ and the velocity profiles close to the wall to see if the boundary layer is contained within the inflation layers)

@fauzaniman9846 2 ай бұрын

Hello sir, thank you for the video. For guessing the number of inflation layer and its geometric growth rate, can we just make a layer height column in spreadsheet, next its total height up to each column number, and next its error% relative to delta_99? Then, simply try different growth rate values and pick whichever combination of N and G gives the smallest positive error% (a negative error% means the inflation layer doesn't capture the boundary layer). My initial thought is that this eliminates the hassle of using root finding methods or using arithmetic and logarithmic manipulation.

@alaajaleel8583 2 жыл бұрын

thanks, Dr. Aydan so please can you explain that in Ansys fluent program

@Sergio-ph4dv 2 жыл бұрын

Does anyone know where can I find empirical values of Boundary Thickness Layer for a fully developed turbulent pipe flow? Thanks!

@fluidmechanics101 2 жыл бұрын

... technically when the flow is fully developed the boundary layer fills the entire pipe. However, for meshing the inflation layers normally a good choice is 10% of the pipe diameter

@hardiksharda9673 2 жыл бұрын

Amazing! Your videos are helping me build a strong foundation in CFD as a beginner. I have sent you a LinkedIn request. I would like to discuss and clear few doubts regarding Masters in CFD. So if you are okay with it please accept my request 🙃🙂 Thank you Dr. Aidan. Really appreciate the efforts!

@fluidmechanics101 2 жыл бұрын

I don't really use LinkedIn, so best to post your questions as precisely as possible in the comments or just send me an email (fluidmechanics101@gmail.com)

@hardiksharda9673 2 жыл бұрын

@@fluidmechanics101 Thank you Dr. Aidan

@parthpadhiyar4732 Жыл бұрын

Hello mr. Hardik Sharda Your comments were really helpful for me to achieve proper results in cfd Thank you so much for helping me

@nurudin99 Жыл бұрын

Very informative video Dr Aidan. I have doubt, if my cfd analysis involve blade with hub and shroud, do i still need to put the prism layer on the hub and shroud?

@fluidmechanics101 Жыл бұрын

Yes, if you want to calculate the total drag (and hence pressure loss) correctly

@nurudin99 Жыл бұрын

@@fluidmechanics101 thanks for the reply Dr Aidan

@davidbenalcazar9589 3 жыл бұрын

Hey, what do you think about mesh quality of the first layers of the inflation? I have performed some cases using inflation for an external flow simulation and the first layers of inflation (wedge element, similar to a pizza slice) get a low quality value. Despite of that, the flow behavior near to the ground is totally better than only using tetras. Thanks for this valuable information. Thumbs up!

@fluidmechanics101 3 жыл бұрын

Yes, the first layer often has bad quality because the cells are so thin. Usually most CFD codes are happy if the aspect ratio is less than 2000. For quality, it is worth zooming in and looking at the cells close to the wall. If the mesh lines are roughly perpendicular to the wall, then the cell quality should be fine. The difficulties tend to occur when the mesh lines close to the wall are skewed AND the aspect ratio is high. Good luck with your simulations! Don't get too put off my low quality, your simulation may still run successfully .... Give it a try!

@interfluo6420 3 жыл бұрын

For a rans calculation with refinement regions, does the same suggestion apply with regards to the cell volume transition? More specifically, the transition area should be placed in an area with low gradients? Also if a case has a high cell volume translation after the inflation layers, but the inflation layers span well beyond the boundary layer, is the concern lower because of the relatively low gradients? Thanks for the education!

@fluidmechanics101 3 жыл бұрын

Yep, that seems sensible. You can get away with a sudden volume transition if you are away from the areas with high gradients that you care about 👍

@interfluo6420 3 жыл бұрын

@@fluidmechanics101 fantastic. I am really looking forward to more videos on meshing, the more CFD I do the more I realize the importance of meshing. Topics I have been asked a lot about and find interesting involve moving mesh and AMR. for AMR maybe you could talk about the different data structures and time marching techniques associated (global vs local), along with pros, cons, etc..

@ivangomez2292 3 жыл бұрын

Nice explanation video. a question, it is not necessary to put layers in walls far from the surface/zone of interest or every wall in my domain must have boundary layers?

@fluidmechanics101 3 жыл бұрын

You should put the layers on the walls where you need an accurate solution for heat transfer, forces, lift, drag and where you need an accurate boundary layer to develop (such as the inside of pipes and the walls / floor approaching your object of interest) . Usually you will need to put them on the majority of your surfaces, unless the surface is unimportant for the accuracy of your solution.

@abdelhak.keddouda 3 жыл бұрын

Hello Dr Aidan, You are doing a great work, thank you. I only have a side question, that is what are the softwares used to create plots, diagrams and figures in your presentations, thank you.

@fluidmechanics101 3 жыл бұрын

I make all my figures in inkscape. You can get it for free and use it on any operating system. Would definitely recommend inkscape!

@abdelhak.keddouda 3 жыл бұрын

Thank you Dr. Aidan, absolutely going to use it for my future projects 😀

@praneshdewangan Жыл бұрын

Great video, so much to learn here. I have a question regarding the variation of y+ for mesh refinement studies though. How much do you advise the variation of y+ in different cases? for eg: for a case where I am targeting y+30, shall I take 30, 40 and 50? it would be a great help if you can clarify this. Thanks!

@fluidmechanics101 Жыл бұрын

I think that covering an order of magnitude with your changes in y+ is a good idea. So y+ = 0.1, 0.2, 0.5 and 1.0 would be a good idea, or y+ = 30, 50, 100, 300. If you make the values too close together, then it can be difficult to see the changes in the solution. For example, y+ = 30, 35, 40, 45 probably wouldnt be as useful as 30, 50, 100 and 300. If you then find that the changes are large, you could refine you search afterwards. For example, if you tried 30, 50, 100 and 300, and the results change a lot, then you could add extra data points and try 35, 40, 45 and 55 afterwards. This is likely to be case dependent, so try it out and see what you find!

@praneshdewangan Жыл бұрын

@@fluidmechanics101 Thanks a lot for explaining it so clearly.

@RafaelOliveira-m5j Ай бұрын

Great video! My case study is tubular heat exchanger. Where can I find the equations for internal flow in order to calculate the boundary layer thickness (δ99)?

@fluidmechanics101 Ай бұрын

The BL fills the pipe in an internal flow. Use 20% of the pipe diameter instead as a reasonable estimate

@RafaelOliveira-m5j Ай бұрын

@@fluidmechanics101Thank you for your reply! Do you have a reference that expresses this correlation?

@RatDota 7 ай бұрын

You mentioned that for RANS, we want to avoid a large volume transition as it can lead to an error in the local gradients. Isn't the error dependent on the size of the cells, rather than on the growth rate? E.g. could you not have really small cells with a large growth rate, and still have small gradient error as long as the cells continue to remain small enough?

@francfrancois486 2 жыл бұрын

If I'm getting vastly different results for small variances in mesh (e.g. changing growth rate from 1.2 to 1.25 with N=7 and Yh=0.1mm causes drag to change by several percent), what is the first thing I should be looking at to reduce mesh sensitivity or to get a more trustworthy result?

@fluidmechanics101 2 жыл бұрын

If you are getting vastly different results then your flow field is probably quite different. Have a look at the flow field overall and see if you can see what is happening. Do you have flow separation? Is the separated flow very different? Once you know what is happening try and work out where you are getting most of your drag from. Then you can look at the mesh in this particular region and see how refined it is. Is your y+ locally very large? (Remember that y+ varies everywhere). Also, is your flow field unsteady or steady? You may not be resolving the flow in time and might be looking at two different snapshots. These are all just guesses as I don't know what your flow is 😅

@NB-zj4yv 3 жыл бұрын

Can you make a video about size function and mesh density distribution?

@akarshshetty9262 Жыл бұрын

Hi Aidan, you mentioned that dU/dY is more for RANS and hence a wall normal resolution is necessary and if we were to perform LES simulations dU/dX comes into play and resolution of cells also needs to be done along the wall. Is it a characteristic of the analysis type itself that gives rise to these gradients or does a combined dU/dY and dU/dX variation exist in flows in nature?

@fluidmechanics101 Жыл бұрын

An easy way to think about this is to think about turbulent eddies. In LES and reality, there are very small eddies close to the wall, which we need to resolve. These have gradients in the x, y and z directions which we need to resolve. In RANS we don't resolve these eddies so we only need to resolve the gradients in the mean flow variables in the y direction

@akarshshetty9262 Жыл бұрын

Thanks for clearing that up!👍