XFlow
 

Hello,

Anybody has any experience with XFlow?

Thanks,

Yaping

..................................

Hey,

I am using XFlow, How can I help?

Thanks

hi Saket.

Given your experience with Xflow I'd like to ask some questions about it:

1) could you point me to any paper or verification and validation for external , subsonic aerodynamics testcases in which Xflow is used?

2)could you compare the solving time, given the same accuracy, with fluent, starccm, etc...

3) just out of curiosity: how did you came using it? i tried to get a demo licence but the reply was negative... frankly speaking, their hope that i pay 50k€ for a software I've never seen before is wishful thinking. just wandering if other users have bought it because they were sure that it was the right tool for the job or... dunno.

thanks.

Hey Sail,

In the interest of full disclosure, I work for MSC in the XFlow team.
- Certainly have validation of external aerodynamics on academic problems that are well researched e.g ASMO car model and real industry problems with our customers. The customer data is sensitive as you can understand, I can certainly share other data with you. If you are interested to take a deeper look into XFlow we can talk about how we can accomplish this including trial.
- When you say comparing time, I assume you want to see how much time it takes from the time when one starts to do a simulation, this includes importing the geometry, cleaning up, meshing, setting up the analysis, run time and post processing. When one starts comparing this you will find that the time invested in bringing in CAD models, cleaning up and meshing is eliminated in XFlow...which is the bulk of the time in doing simulations with traditional CFD software's. Users can focus of doing more design iterations in their product development in the same time period.
- I agree with you, I would feel the same way that paying $$ for a software I have never tried doesn't sound like a good idea. We are not looking to get $$ this way either....we would engage with the company and show how XFlow will impact their product development by saving time, saving $$, increasing throughput.
- XFlow is a paradigm change in CFD, when someone says no meshing...first reaction is WOW and also skepticism. Our customers have seen the value it brings to their product development.
- We would love to engage more and show you more in depth into the technology. I have myself used several CFD software's and I still manage to amaze myself everyday running XFlow.
- I am saket.chaudhary@mscsoftware.com, send me note and we can dive deep into XFlow.

Check out the below
http://www.youtube.com/user/XFlowCFD

Thanks
Saket

Hi Saket.

Thank you for your prompt reply. Your software is interesting, and i'm writing you an email to have a private feedback.

best regards

Hi Saket,

when looking at the simulation results provided by Xflow http://www.youtube.com/user/XFlowCFD
it's terricfic !!

I even don't think that there exist other softwares able to perform the kind of simulations Xflow did. I think you are 100 light years away from Fluent, Star CCM+ and others.

But....

How did you validated your results ? How could you assure that your computed results are good?

I guess you have performed some benchmarks on classical flows where other numerical or experimental results are available.
Did you communicate on this ? Where are your comparisons?

Have you also compared your results in the case of a high resolution DNS turbulent flow (channel flow for example) where huge databases (velocity field statistics) are available one very fine grids ( 4096^3 ~68 billions grid points ) ?



yes it will be interessting to know for a very complicated flow (complex geometry, complex physics ) how much time it takes from the starting point until post-processing?


But also the CPU time only required to compute the flow, for example during 10 physical seconds of simulations ( how many time steps, the magnitude of the time step...)

What is the overall precision of the method ? first order, second order, higher?

Is XFlow based on lattice boltzman method like the code Powerflow?

I'm not familiar with the capabilities of engineering codes like Fluent and such, but there are many and more research codes that are able to perform this kind of simulations and do so routinely. However, these codes are generally not open to the public or are in some cases classified. These videos are certainly nice, but similar stuff can be seen at decent CFD conferences as well. I'm not saying that they are not impressive, but let's keep it real :)
[quote]
But....

How did you validated your results ? How could you assure that your computed results are good?

Again, I haven't worked outside academia, so this is new to me as well. How in general are commercial CFD codes validated? Are there publications/papers about this kind of stuff? Nice and fast pictures are one thing, but there's no free lunch in CFD. If you want to be lightning fast, you have to sacrifice accuracy.... So anybody in the know, are there any publications about the accuracy and even consistency of commercial codes available?

DNS codes are almost always of a spectral nature, and I sincerely doubt that XFlow has a spectral basis, so the comparison with a high RE DNS is not so relevant in my opinion. What I would like to see before I touch any piece of software not written by myself or proven is this: Does the solution of XFlow converge to the DNS solution for low/moderate Re? At what cost?

Is there any organization/publication that compares commercial codes in terms of accuracy and efficiency?







Yes, interesting!

If there are research codes able to perform this kind of simulations I would like to know which one?

On a very specific point you can find a research code able to do it. I mean if you take a code dedicated to free surface flow for example it will be perhaps able to perform one of the simulations seen... But this research code won't be able perhaps to manage in the same time
moving meshes or coupled FSI or heat transfer etc....

generally research codes are very specialized in certain tasks and not versatile like commercial codes.

Why I was so amazed by Xflow it's because of the performed simulations in a lot of very different areas ( automotive, aerospace, aerodynamic, free surface flows, FSI, heat transfer,..)
None of existing research codes are able to perform well in so different areas.
Just for full disclosure I'm from academic side and I do not sell any commercial code nor use none of them in my research activities.

ok, I agree with you on that point. There are some versatile research codes like the ones used i.e. by Onera or Airbus or academic research groups and such that can do compressible/incompr, FSI, heat transfer, but in general, you are right, research codes tend to be very specific in what they do.

Maybe it's true, I don't claim to have an overview over all the research codes out there, I'm just saying that I'm not convinced of XFlow in terms of accuracy. We have no way of telling how "well" it actually performs. Take the flapping wings for example... it would look equally impressive even if the drag and lift were totally off the mark...


I agree with you that it's impressive to see how many codes/methods have been coupled in this approach, and nice to see that it works - at least on a qualitative level. However, without careful validation and verification, which has been published in reviewed journals, it remains - at least for me - pretty pictures....

Cheers

you are right and I have to admit that the code CEDRE from ONERA can do indeed a lot of stuffs even if it is very specialized in multiphasic reactive flows. But for example if you want to perform aeroacoustic you have to switch to another product of ONERA named SPACE.
It is in that sense that verstatility of research codes are weaker than commercial ones. And CEDRE is probably one of the most versatile research code.

You got it !!
Yes I totally agree with you and that was my point in my first post.
Without a tons of rigorous validations and the communication of the real cost (CPU time) for some given benchmarks attested by published papers in high level reviewed journals, these impressive animations will remain nice moving pictures.

The flapping wings is indeed a very impressive example, but who can say it is right and accurate?
We just need to be convinced to believe it.

Thanks Guys. So we agree that the technology is innovative and designed to help bring down the barriers from traditional CFD by giving power to the users in doing more design iterations in less time.
I agree with your points that users of the technology who invest $$ will have to see if the technology fits their application, solves problems in acceptable engineering time and accuracy.
If you are interested in using the technology send me a note and I can share validation examples and also have your own models run in XFlow to show the correlation. Totally on board with your thoughts that seeing your own products is best way to believe.

Thank you for your reply, Saket. Could you please comment on the question of validation and accuracy of XFlow? That would be highly appreciated! thank you!

Cheers!

How about doing an analysis on the aircraft from the Drag Prediction Workshop:
http://aaac.larc.nasa.gov/tsab/cfdlarc/aiaa-dpw/

I would be interested in the results along with documented steps going from geometry to post-processing, including associated times.

Hey,

How about the high lift prediction workshop.
http://hiliftpw.larc.nasa.gov/

We have done the high lift simulations which shows the coreleation of XFlow results with the NASA test results of drag, lift, polar curve etc.

Please ping me at saket.chaudhary@mscsoftware.com or at +1 804-405-1242 and I can share the results with you.

Best,
Saket

Saket, your results from the high lift workshop are of interest as well, so I'll send you an e-mail request.

However, I mainly conduct cruise analysis (as do many other external aero engineers), and the drag prediction workshop is of higher interest. Please add it to your company's to do list.

Thanks

XFLOW userguide
 

I am a M.Sc. student.
Can anyone send me the userguide of the XFLOW?

Thanks in advanced;

sarfaraz@alum.sharif.edu

I could do that today in 2 codes and if I spent time may be around 2 more weeks I could do that in 4 codes.

Currently that could be done by:
1. The in house code that I wrote for my last company. We could do that for last 4 years. Validated the results against experimental data from wind tunnel too.
2. Inavier has immersed boundary so it can also do it.

I could do:
3. I have written 2D versions of lattice boltzman that support immersed boundary. If given time I could write down 3D versions too that would work just like xflow.

4. Now that I could program starccm too, I could add immersed boundary and could do that with it too. It won't take more than 2 weeks to do that.


Further I assume fluent had immersed boundary code long ago so that could have also done it. And Ansys CFX also has immersed solid , so i guess that could also do it.


Other than that literature is filled with cases where people have done this type of thing. From acadmics I can tell you that inhouse of Tohoko univ of Prof Nakahashi's group can also do it. Probably frontflow also can do it.

Excuse me, with all respect, but LB need indeed mesh.
Some people use LB models based Cartesian, orther on spherical, etc.
Some people use refinned meshes in LB too.
It is at those mesh-nodes where collisions happen, usually modelled by the SRT BGK/Wallander model or MRT.
So, where the meshless-myth come from?!

You are correct. In fact the dependency of LBMs on mesh is one big obstacle in path of LB Methods. Also trying to get it to work on general polyhedrals is not easy, specially when viscosity and delta T depend on type of streaming which in turn depend on mesh type. (like classical streaming can not be applied to general meshes directly).

Why do you want to work on (general) polyhedrals when dealing with LB?

You wrote: "when viscosity and delta T depend on type of streaming which in turn depend on mesh type"

You have flow velocity u, in lattice units, which is limited, up to a value depending on the model. Then, you have a characteristic length L, so the only way to increase Reynolds number is to decrease the kinematic viscosity nu=(tau-1/2)*R*T*(delta T). With Delta T =1 fixed, decrease the relaxation time tau, which might lead to instability.

What do you mean with "streaming which in turn depend on mesh type"?

If you meant the stream step, it is supposed to be from one one to another, and that step is supposed to be fixed. If the boundary is located between nodes (due to the geometry your gas is inmersed) you use interpolation (there is a paper from the people from Exa) and it guarantees conservation laws.

There are LB models relying on (around) Cartesian, Spherical, etc, but there is a price to pay when dealing with such non-Cartesian grid.

Again, what is the point to use (general) polyhedrals when dealing with LB?

As to why I want to work with LBM's with general polyhedrals is for the reasons that they represent the shape much better compared to the approach that involves cube. Another approach is the surfels that exa use to represent bodies. Well the factor of 1/2 in the viscosity formula you have is due to the streaming step of classic lattice boltzmann (which you said is fixed). But as soon as you move into finite difference and finite volume that term (1/2) disapears. This is why I said that streaming depends on the mesh, on certain meshes you could apply the streaming that you mentioned. On others you do it by using finite difference method or finite volume methods or using interpolations etc. There is a good paper explaining viscosites in each approach, give me time I will find the title of it. I have a hard copy of it.

Yes, but by using finite difference schemes (FDS) and/or finite volume methods (FVM) you are violating the main LB idea. N-S based CFD and LB based CFD have difference physolophies. Any way, please, give me the paper title and journal number, page, etc so I can download it myself (when it suits you :) ). Thanks.

PS: BY the way, are you working at X-Flow, Exa or? Just curious :)

I am working at CD - Adapco. I am just interested in LBM for fun of it. I usually take up something that is not related to my work and learn it. Spent time with meshless methods but LBM I think have more appeal. Tomorrow I will give you the paper's name. About stablity if you are interested, I find his work very interesting. http://www.rbrownlee.org.uk/index.php

I found the name of the paper "Viscosity of finite difference lattice Boltzmann models" by Victor Sofoneaa, Robert F. Sekerkab, I have a pdf of it, if you want pm me your email i will mail it to you. Its a good read.

Thanks, I know that paper, and I have it. Thanks. The issue is that the use of FDS and/or FVM insert numerical dissipation, which is not desirable. Im aware of that many people are using so in LBM. I don't follow that path.


On another matter:
According to Exa, their constraints is Re < 10,000
SOURCE: http://exa.com/core-technology.html

1000 < Re < 10 000 can be reached for grid resolution far less than 10^3, as seen in fig 6 in this paper
Mathematics and Computers in Simulation 84 (2012) 26–41 (http://www.sciencedirect.com/science...78475412001966).
Interesting that paper compares two different LB models and they give similar results.

However, no information if provided about their implementation in Exa or X-flow.

So my main question are:
1-Is Exa using finite difference schemes, volume method, or in the implementation of the LBM?
2-What about X-flow?

The only thing I know is that X-flow uses "MRT and refined-schemes". Beyond that, not sure about their implementations.

Thanks in advance :)

Thanks for the link. I am not well aware with x-flow but with PowerFlow i have fairly good idea. They are using single relaxation model, with the classical streaming ( fbar = f) so they are not using finite difference though it seems have published something separately (not in powerflow). I have some papers they published that outlines what they do. I can try to scan them into pdfs if you are really interested. They have this series of voxels of different sizes, typically ratio is 2 in length dimention. Number of solves vary on each size, so if coarse cell get N updates, finer children of it would get 2N updates (or delta T is half of coarser one). To join these fine and coarse cells they use liner interpolations. Currently their mesh is once generated then fixed during the iterations but they are looking into dynamic meshing and mesh movements (inferred from their job postings). Also about their limit of Re=10000, I think they are saying that uptil this Re they could run it without any turbulence model, after that if mesh is not fine enough they would need turbulence model. which actually should bail them out of stability issues too. My very personal opinion (which I can not verify or prove) is that Powerflow uses some kind of entropic update to keep the solver stable even on higher Reynolds numbers. Also I believe that speed of classic lattice boltzmann is main reason they are not using other LBMs, even though they are fully aware of developments of various other types of LBMs. (again this is an opinion).

I'm aware of the paper you are refering to by people of Exa.
But that construction is not local, unfortunatelly.

If you are refering to Entropic LB (ELB) model, well, the paper
Mathematics and Computers in Simulation 84 (2012) 26–41 (http://www.sciencedirect.com/science...78475412001966).
shows that in 2D, the ELB is no better than the other one.
There are other papers where 1D comparisons are made, and still the ELB is no better thatn the other one in 1D shocktube.
Hence, there is no evidence that in 3D the ELB would be better, at least no independent people have tested anyway.
These comparison are made by independent people, while the ELB creators still claim otherwise.
There is an ongoing controversy seen on http://pre.aps.org/abstract/PRE/v84/i6/e068701, but that is another story.
Maybe EXA is using positivity rule, to maintain positive populations, to avoid instabilities.
Not sure. There is always a price, e.g. in the accuracy, since the issue is the boundary conditions, as shown in the aforementioned paper.

There are hidding tricks at the boundaries, as usual.

The question is: If PoweFlow is under/over predicting turbulent flows (according to some complains, never sure,
but it what it is said in some forums) then:

Is that due to their turbulent models?
(It is well known than RANS can even given the wrong direction of the swirl, due to the modeling).

What about the performance of PowerFlow and X-flow compared to other NS CFD codes?

Are LB CFD codes faster? How faster? Two fold?, Three fold?, etc

One thing is for sure: The car industry has NOT rejected the use of LB in CFD, as seen here: http://jobs.gm.com/job/Warren-Vehicl...48088/2687218/

I mostly agree with your assesment about stablity. I do not have much opinion of it at the moment because though i have seen papers showing that it is stable and all , but I do not have first hand experience of it. By this I mean, like for example take starccm type solver, I have lots of experience with it and can say lots of things with confidence about its behaviour. But since I have never implemented entropic version myself and have not tried it on complicated cases, really can not conclude anything. Also about PowerFlow over predicting turbulence etc, it is really difficult thing to comment on, as it depends on lots of factors, their turbulence model being cardinal of them. About the performance, which is again tricky, for the same mesh sizes one it seems Powerflow would be faster than codes like fluent and starccm+ . It could be same speed or less efficient (not the word efficient, some solvers might take larger time step) than well implemented direct solvers based codes (that use FFT etc for pressure). On the other hand, one could run calculations with much smaller mesh sizes and also run steady runs to get results much faster than powerflow with say starccm+ . For transient problems related to external aerodynamics , it sounds most attractive.

Anybody has any experience with XFlow in FSI
 

Anybody has any experience with XFlow in FSI
nect to solid solver....
Trying to connect to solid solver.... ,what's mean ,searching for nastran solid.exe

Hello, Anybody has any experience with XFlow? Thanks,
 

Hello,

Anybody has any experience with XFlow?

Thanks,

x flow wind turbine
 

hello everyone

i have one question
can you help me that how can I set the rotor free to rotate due to the forces exerted by the wind?

Hi Saket

MSC also owns scFlow, scTetra and scStream, which are pretty good CFD programs. How would you compare xFlow with say scFlow in terms of speed and accuracy?

Thanks