Introduction to stationary turbulence modeling (RAS) - Part 1

[@mathiassnderskov7214]

Love how you show theory and dig directly down to code to highlight where stuff happens! Thanks.

[@OpenFOAMJozsefNagy]

I am glad.

[@akashcast]

just finished your basic and intermediate tutorials. Your videos are clear, have perfect pace and helped me begin to understand OpenFOAM. Looking forward to seeing more :)

[@OpenFOAMJozsefNagy]

I am glad!

[@Ballba365]

Thank you Jozsef, I am finding your tutorials a great help, I look forward to watching your future videos.

[@TongShaLexie]

Thank you so much! This is so helpful for a new OpenFOAMer🤣

[@obione6757]

this video make too much sense :DDD. I have been trying to understand k-epsilon and omega models and what nut means and you solved my problems. Thanks a million

[@souravkanthal2796]

Thanks for this beautiful lecture

[@JZ1917]

The code walk through part is too fast for me, but since my experience with C++ is close to zero and this is just a "skim through" of the code, I still think it is valuable to have it here. Thank you for taking the time to do these videos!

[@OpenFOAMJozsefNagy]

I am always glad to help.

[@syedmujtabahussaine4355]

Very informative, Thank you.

[@VinnieDreher]

Boss, you're amazing.. Maybe some motorbike tutorial? Cheers

[@kendalmalone705]

Hey Joszef, i got a small question. I'm working on a case right now and i have given a "free stream turbulence level" of x,x%. Is this equal to the turbulent intensity you are talking about at min 11:00 ?

[@007aha1]

reallllllllly gut

[@joseyovanygalindodiaz4767]

The best material

[@pingchang5584]

Hi József Nagy, thanks for your viedo. It is really helpful, I am a new to OpenFOAM. I have a small question, what do the nut and nuTilda mean in this case? Thank you very much.

[@OpenFOAMJozsefNagy]

+Ping Chang ntu is the turbulent kinematic viscosity and nuTilda is an auxiliary quantity for the Spallart Allmaras model.

[@pingchang5584]

+József Nagy Thanks a lot

[@thear1032]

Thank you very much for your nice video.

[@OpenFOAMJozsefNagy]

I am happy to help.

[@raulgrunewald4055]

Hi! Thank you very much for the video! I have a question, I understand that this is a 2D case, but if you want to solve now the same case in 3D, for example using 0.15m depth, how would the characteristic length be calculated?

[@OpenFOAMJozsefNagy]

Usually the area/circumference.

[@stormpeanut9205]

Really really really helpful. If you have time, can you make tutorials about the unstatic mesh??

[@OpenFOAMJozsefNagy]

+Vũ Đỗ Quốc Do you mean unstructured?

[@stevenforrester5760]

Jozsef, the tutorials are very helpful and hope you keep posting more videos. Could you add a link to the notes you refer to you in the video. Thanks

[@OpenFOAMJozsefNagy]

For example Ferziger and Peric: Computational Methods for Fluid Dynamics and similar books.

[@stevenforrester5760]

József Nagy Great, I purchased the book. When I took CFD in Grad School we used the John D. Anderson book so it is a little dated. Cheers!

[@andrestapia85]

thanks for the video! it is very clear and usefull!

[@OpenFOAMJozsefNagy]

Thank you!

[@TheHarishkg]

HI Jozef , can u do a video on OvrPimpleDymFoam ? Thanks

[@OpenFOAMJozsefNagy]

Yeah, maybe in the future.

[@TheHarishkg]

József Nagy hi,thanks for the reply :) would be helpful .

[@vanduyenvimaru6835]

Dear Sir, Thank you for your tutorial, actually it is so helpful. In your video, you calculated epsilon coefficient with considering of value of L. In my problem, I want to simulate a flow around a cylinder with diameter is d and length is L. So I have a question: When I calculate epsilon, will I use diameter or length of the cylinder? Best and regards.

[@OpenFOAMJozsefNagy]

I would use the diameter.

[@vanduyenvimaru6835]

@@OpenFOAMJozsefNagy Thanks for your reply!

[@christianalvarez9930]

Hi! I have two questions, first: Do you have any reference for the kinetic energy equation? k=3/2(Uref*Ti)**2 Second: What do you mean with " L=characteristic length scale"? Thank you!

[@OpenFOAMJozsefNagy]

Try and google them or look it up in a book about turbulence modeling. They are rather common. I don't have a refernce on my hand, I would have to look it up myself. They are also used in Fluent.

[@HoaiThanh-wm6ze]

I also the same question. what is the length scale? I have read in the google and wiki but I can't understand length scale. you can explain for me. my problem is a airfoil (chord 1m, Uref = 33 m\s, Re =2*10^6). I want to set up RANDS mode with K-omega SST. can you help me, please ?

[@shiqiwang3560]

Hello, I have done this example after your tutorial step by step and it works very well. I've learned a lot. However, I want to modify the boundary condition from velocity inlet to pressure inlet because in most cases , we only know the inlet pressure conditions rather than the inlet velocity. I changed the initial conditions to : p inlet : total pressure, fixed, uniform 200(relative pressure), outlet: inletOutlet, inletValue uniform 0; U, inlet, pressureInletVelocity, outlet, pressureInletOutletVelocity. Sadly, it didn't work. Could you please show me a method to make it work? Sorry to disturb you again.

[@OpenFOAMJozsefNagy]

I would use fixedValue for p on both the in- (200) and the outlet (0). If that works, I would set p to totalPressure and see if that works.

[@shiqiwang3560]

József Nagy I have tried fixedValue condition but still failed. Have you succeeded trying to do this?

[@OpenFOAMJozsefNagy]

Shiqi Wang Yes I did run simulations with these conditions. I am sorry, but it is difficult to solve a problem over YoutTube comments.

[@OpenFOAMJozsefNagy]

Shiqi Wang With this tutorial 200 on the inlet does not make sense, because the pressure range is one order of magnitude lower, plus in this tutorial case the pressure is also negative around the step. An inlet pressure of 200 is rather off in this tutorial. What you can try for your case, is calculate your geometry with an inlet velocity, that produces the correct order of magintude of pressure on your inlet (~190-210). Then you will have a velocity and pressure field that is closer to your actual case, then you could switch in the last iteration with the velocity inlet the boundary condition to your pressure boundary condition. Hopefully the solution will converge.

[@ashutoshsingh-et7vm]

Hello sir if you have any codes for jet impingement cooling pls share me it would be great help

[@OpenFOAMJozsefNagy]

Unfortunately not.

[@fitnessmythwalakaka]

Hi Jozsef! Thank you for your videos, I find them really useful! Could you please clarify if the l = 0.07L is acccurate? for K-epsilon? Because I found this one the openfoam documentation for the k-epsilon solver and it says that l = L. The link to the documentation is given below: www.openfoam.com/documentation/cpp-guide/html/guide-turbulence-ras-k-epsilon.html Thank you for contributing :). Really appreciate your work. Regards Shafik

[@fitnessmythwalakaka]

Hi Jozsef! I have realized that you are right! www.cfd-online.com/Wiki/Turbulent_length_scale Thank you for your work! Keep it up

[@OpenFOAMJozsefNagy]

It is a rule of thumb. A lot of people say a lot. You can check out the specific boundary condition for turbulent inlets in the newer version of OpenFOAM.