[CFD] Pressure-based Coupled Solver (Part 2)

[@NanoActuator]

Most of KZbinrs do not provide such valuable information about solvers, especially useful what solver to choose considering different cases. Thanks

[@teodorbabic8007]

Looking forward to a video on density-based solver! Great job!

[@berkaysimsek3011]

Such a clear and brilliant explanation. Thank you for your amazing effort! Looking forward to video on density based solvers.

[@ПавелБеляев-з3ж]

Thank you sincerely for your lectures! Wish we had such teachers.

[@rafaortwein6646]

Fantastic explanation! So nice to follow! Many thanks

[@prasanthvemula_nv]

Thanks brother. I was solving the exact same problem in microfluidics using mixed convention. Your video are helping a lot for me and my college mates.

[@mahmoudsaleh9006]

Thank you so much for such amazing explanation, not only for this session but all your videos. I would suggest a new topic if you do not mind, it the grid generation. The gird generation techniques, algebraic or elliptic grid generation, are explained briefly in the references. Also they did not provide sufficient- worked examples.

[@Jialei-dw3li]

Thank you Aidan, by combining the coupled algorithm and pseudo-transient method, I think I more or less grasp the essence of the so-called coupled flow solver used in many commercial CFD software (e.g. Star CCM+ and Fluent).

[@fluidmechanics101]

Fantastic. I don't think we will ever know all of the details, but at least we have enough understanding to know which solver is which!

[@derekmitchell209]

Great video! Thank you for making this series. I noticed an error in equation 14 (around the 15 minute mark). The face area (A_f) has been dropped from the last two terms.

[@hungnguyenthanh8833]

You are really genius 🙂🙂🙂. I hope that you can offer many more lectures

[@RajeshwaranK-z6b]

Thank you for your valuable content 👏

[@kohinoor9070]

Great video! Can you plz make a video on GEKO model as it is turning out to be new standard for turbulence modelling. Thank you.

[@giovannicaramia859]

As always, good job!👍🏻😎

[@cfduser]

Do you ever plan to cover choked and supersonic flows, density based solvers, etc? There is probably endless discussion there

[@gaetanjamet1477]

Saved my day !!

[@mohamadfawaz4146]

Fantastic !

[@is-ig4zh]

Thank you Dr!

[@jacks.554]

A very nice video! I think there is an error in Eq. (8), (9). The weighting coefficients omega and (1 - omega) should be swapped. Thanks, Aidan ;-)

[@fluidmechanics101]

Well spotted. Thank you!

[@rccabrales]

Excellent video, thank you for the great job...I suggest a similar video but using the projection method introduced independently by Chorin and Temam at the end of the 60s.

[@minjoong6687]

Thanks alot for the great lecture Sir! One qustion please. The matrix shown when you mention about 'Saddle point problem', seems not to have that problem if continuity equation goes on the top of the matrix. (I mean, if the unknown's order is P-u-v from the top.) Is there any method of resolving the saddle point problem like this? - Best regards from South Korea.

[@meenakahimalhan2499]

very informative video, thanks, could you please make a video how CFD codes calculate lift and drag forces over vehicle or airfoils.....

[@robbiewilliamson9783]

In many of these videos it states that we should remember that all of the flow variables vary linearly across the cell face. Could you point me towards a video where you discuss why this is the case? Thanks (brilliant videos)

[@fluidmechanics101]

It's a feature of the 2nd order finite volume method. If we assume that the flow variables vary linearly across the face, then the integral across a face is equivalent to the value at the face centre multiplied by the face area. (This is sometimes called the midpoint rule). It's a neat trick that lets us convert all face integrals into the value at the centre multiplied by an area (an algebraic equation, rather than an integral). So it is the feature that ultimately allows us to convert all of our equations into matrix form (linear algebraic equations) and then solve them, but it isn't explicitly stated anywhere.

[@robbiewilliamson9783]

Ah, great. That makes sense. Thanks! @@fluidmechanics101

[@franciscoxaviergonzalezrom4648]

Thank you!

[@mariarosales3535]

Thanks sir for the lecture. Does the use of either coupled or segregated solver's, even when achieved monotonic convergence in steady, can result in different solutions for the same simulation conditions? It's somehow to know if fields would end up to have drastical difference between them when using one or another

[@fluidmechanics101]

Difficult to say. I suppose this would depend on what CFD code you are using and how rigorously they have checked it 😀 in theory they should be the same of course ..

[@roopakbaliyan5935]

Best.

[@Random-sm5gi]

Hi! Can you touch on the topic of “particle cloud” in the context of Lagrangian modeling?

[@xiasuyang6556]

Does the coupled solver also treat RANS variables and passive scalars implicitly?

[@pablogarcia5094]

Hi, Aidan/all. Is there a good reference text book that I could use to understand pressure based coupled solvers that also discusses the effects of compressiblity? The CFX theory guide has very limited information about how compressibility is treated in the form of linearizing the (rho*velocity) term by recasting it in the fully implicit form, but that does not help me understand the concept very well. Appreciate any guidance with the above. Thanks.

[@fluidmechanics101]

Sadly I don't think there are any good sources besides the user manuals. If you find any, please let us all know!

[@pablogarcia5094]

@@fluidmechanics101 Will do. Thank you for all your work!

[@pablogarcia5094]

@@fluidmechanics101 Getting back to the above exchange on the treatment of compressibility in pressure-based coupled solvers, I did some looking up, and found that a lot of work has obviously been done in here outside of CFX. I will mention two references below, and hopefully anyone interested can snowball from there. "A coupled pressure-based computational method for inompressibe/compressible flows", Chen, Z.J and Przekwas, A.J is more of a reiteration of the numerical discretization presented in the CFX manual, but offers some additional clarity on the treatment of the convective flux term. However, I found "The segregated approach to predicting viscous compressible fluid flows" by Van Doormaal, J.P, et al. more informative in terms of understanding the purpose of linearizing the mass flow term. After some reading, my understanding of the treatment of compressiblity in pressure-based coupled solvers is the following -- the Rhie-Chow discretization of the advecting velocity term introduces the pressure coupling (as is elaborated on in this video). Meanwhile, the density is linearized in terms of pressure in a manner that introduces the compressiblity which is evaluated isothermally. This results in formulating an equation for density in terms of the pressure from the current and new timestep. The above two terms (velocity and density) when plugged into continuity equation, and linearized in a standard manner, now produce the new diagonal and off-diagonal coefficients for the pressure equation that satisfies the hydrodynamic system while also accounting for the necessary compressibility in the flow. I hope I have been clear in my summary. Please feel free to critique my interpretation if you find something wrong about it. Thanks.

[@fluidmechanics101]

Great findings! Thank you for sharing

[@ThetZin-xw3zg]

😍😍😍

[@hcelik]

Do you have access to the "H. Jasak, 'Coupled Flow Solution Algorithms in OpenFOAM', TOBB ETU, Ankara, 23 October 2019" reference? It could be nice if you may share with me. Thanks.

[@snared_]

guess not?

[@franciscoxaviergonzalezrom4648]

Sir, how could I contact you?

[@fluidmechanics101]

[e-mail]

[@mahdipashaie1283]

thank you!