One of the foremost challenging topics that has found wide applicability deals with the flow in porous media. The topic has been, time and again, researched with great interest. I have done my share of flow simulations involving porous media and, uptodate, havent figured out "one particular" global model that can be used in a universal manner. It is understandable to assume that every single porous media flow is different and the complexities associated with the interactions within the systems are not easily resolved..Still, to me, using different models for different systems and not able to combine them all together indicates that the fundamental research in this area needs serious revision.
Information on multi scale modelling in porous media can be obtained here http://www.porous-media.org/
A nice handout on porous media here: http://www.columbia.edu/~rl268/ChESite/E3110/Handout_15.pdf
Texas A&M has a nice list of publication reports involving different simulation analysis.
http://www.isc.tamu.edu/publications-reports/tr
Bad that they did not name files easy to open and read as per need. Sample file on porous media: http://isc.tamu.edu/publications-reports/tr/9706.pdf
Another nice website with several papers/documents/files on porous media flows can be found here: http://www.win.tue.nl/macsi-net/Events/
One of Prof. Joseph's page with several papers on cavitation and fundamental fluid dynamics, also has some papers on porous media
(see http://www.aem.umn.edu/people/faculty/joseph/papers/) - the paper is modeling foamy flow in porous media (http://www.aem.umn.edu/people/faculty/joseph/papers/foamyOils3.pdf)
a nice paper for definite reference and further research http://library.wrds.uwyo.edu/wrp/85-37/85-37.pdf
Several softwares are now adept in carrying out flows through porous mediums. ANSYS,STAR,Flow3D,FIRE,openFoam(:),Polyflow(?) - all have a variety of models in-built. Again, directions of usage is based on particular application where the terms involved in the transport equations will be treated appropriately. Based on my experience in coding porous flows, fundamental changes (the GUI in softwares) let you do is to adjust the pressure gradient (based on some interactions) and the drag coefficients. As written in my earlier blog, drag coefficients play a pivotal role in producing excellent convergence and stability rates owing to the nature of the set up of the solution matrix.
A sample FLOW3D movie (Finite Volume method) - Read Flow3D paper on flow through unsaturated porous media here: http://www.flow3d.com/pdfs/tn/FloSci-TN25R.pdf
Youtube video: http://www.youtube.com/watch?v=jszmSsF2gDI
Get more flow3D based runs here: http://wn.com/Modeling_Porous_Media_with_FLOW-3D
Doing porous media flows using Lattice boltzmann !!
http://www.youtube.com/watch?v=F7j8C5-m430&feature=related
I found the following site - http://www.engr.ucr.edu/~vafai/Publications/ very useful. They have a long list of papers on heat and mass transfer with a lot of publications/book chapters on porous media flows.
Modeling and simulating your own porous media flow is now possible - thanks to openFoam !! A sample modeling capability detail is presented here
http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2008/HaukurElvarHafsteinsson/haukurReport.pdf
I followed this researcher : http://www.ifd.mavt.ethz.ch/people/hajibeygi/index with some nice information in the site.
There are loads of papers on multiphase flow modeling in Heterogenous porous media, porous medium flows with fractional distillations, fractured media - with and without turbulence - how complicated can these get??
Thursday, May 19, 2011
Tuesday, May 17, 2011
More on Testing / Validation / Verification
Once the modeling and implementation part is worked out, the most critical and important phase of the code development stares at us. Yes, you guessed it right. The validation part !!
Most often, what is coded in the software (on a theoretical basis) involving detailed physical approximations of a global phenomenon is directly tested against well known "experiments" and "test cases". During the testing (which is pretty much making sure code does what it is supposed to) and later, the validation (where the model is supposed to mimic a process) process, the developer/coder realizes that more approximations or model adjustments is necessary to satisfy the user!!
Stability, convergence, accuracy are all dealt with in the validation process. If the code is made to work on a variety of test cases and the coder, who is the best critique of his own work, tries to break the code by providing a wide range of operating parameters. With every input, the developer monitors the behavior of the code - as to what happens when the code confronts certain aspects of numerical deficiencies or challenges based on the input defined.
Every test case is unique in the sense that it offers a completely new perspective of the modeling process - what the model lacks and what additional effects needs to be incorporated etc. It is not an easy process. No way. However, as a rule of thumb, modelers start by applying the code to smaller domains and escalate the size and complexity of the process as they move into advanced testing/validation process.
For example, once you have developed a "boiling model" - it makes no sense to directly apply it into a large scale channel flows with high complexity when no tests have been run on smaller channels/ducts and compared with experiments. Sometimes, in fact many times should I say, going across different scales and applying the codes, one figures out that some "problems" are often masked by other parameters operating in the system. Only by running the procedure on a wide range of scenarios can one explicitly make sure all modeling constraints act as per plan and their interactions are stable.
A small discussion is available here: http://www.innovative-cfd.com/cfd-validation.html
This site shares some well known validation resources
NPARC Alliance CFD Verification and Validation Web Site: http://www.grc.nasa.gov/WWW/wind/valid/homepage.html
AIAA CFD Drag Prediction Workshop: http://aaac.larc.nasa.gov/tsab/cfdlarc/aiaa-dpw/
CFL3D Test/Validation Cases: http://cfl3d.larc.nasa.gov/Cfl3dv6/cfl3dv6_testcases.html
Sample validation/testing (exp) study links
1. CFD model validation for hydrogen dispersion: Nice study - http://www.gexcon.com/doc//PDF%20files/Middha_Hansen_Storvilk_HydrogenDispersion_09.pdf
2. Stirred vessel mixing test case study released by ANSYS: http://www.bakker.org/cfm/publications/tn253.pdf
3. Often wind tunnel experiments and studies form a large portion of the CFD testing and validation database: I came across one of these sites
http://ftp.rta.nato.int/public//PubFulltext/RTO/TR/RTO-TR-027///$TR-027-02.pdf
4. How about a CFD evaluation study of wind tunnel flow quality itself !!?
http://sts.bwk.tue.nl/UrbanPhysics/CFD_windtunnel.htm
5. one of the openfoam based WIKI has a site for multiphase activities: http://openfoamwiki.net/index.php/Sig_Multiphase
6. I am no supporter of any particular book / reference..recently had a chance to look at this book ("Validation of Advanced Computational Methods for Multiphase Flow", C2005). It was a nice collection of the test cases (fairly well known to most of us)
http://www.begellhouse.com/books/709c03c830e1b733
I found this article sometime ago on the "general BEST practices guide for numerical accuracy"
http://www.kxcad.net/ansys/ANSYS_CFX/help/help/Reference/CDDDFGCH.html
Coding and implementation is one part of the puzzle. Without validation and testing, no software package is complete. (No wonder so many job availability for validation and testing are on the rise !! Customers want to see more validation reports / testing reports before they award any contract to potential CFD consulting services or the big players)
Make sure whatever you code -----> is properly validated.
Most often, what is coded in the software (on a theoretical basis) involving detailed physical approximations of a global phenomenon is directly tested against well known "experiments" and "test cases". During the testing (which is pretty much making sure code does what it is supposed to) and later, the validation (where the model is supposed to mimic a process) process, the developer/coder realizes that more approximations or model adjustments is necessary to satisfy the user!!
Stability, convergence, accuracy are all dealt with in the validation process. If the code is made to work on a variety of test cases and the coder, who is the best critique of his own work, tries to break the code by providing a wide range of operating parameters. With every input, the developer monitors the behavior of the code - as to what happens when the code confronts certain aspects of numerical deficiencies or challenges based on the input defined.
Every test case is unique in the sense that it offers a completely new perspective of the modeling process - what the model lacks and what additional effects needs to be incorporated etc. It is not an easy process. No way. However, as a rule of thumb, modelers start by applying the code to smaller domains and escalate the size and complexity of the process as they move into advanced testing/validation process.
For example, once you have developed a "boiling model" - it makes no sense to directly apply it into a large scale channel flows with high complexity when no tests have been run on smaller channels/ducts and compared with experiments. Sometimes, in fact many times should I say, going across different scales and applying the codes, one figures out that some "problems" are often masked by other parameters operating in the system. Only by running the procedure on a wide range of scenarios can one explicitly make sure all modeling constraints act as per plan and their interactions are stable.
A small discussion is available here: http://www.innovative-cfd.com/cfd-validation.html
This site shares some well known validation resources
NPARC Alliance CFD Verification and Validation Web Site: http://www.grc.nasa.gov/WWW/wind/valid/homepage.html
AIAA CFD Drag Prediction Workshop: http://aaac.larc.nasa.gov/tsab/cfdlarc/aiaa-dpw/
CFL3D Test/Validation Cases: http://cfl3d.larc.nasa.gov/Cfl3dv6/cfl3dv6_testcases.html
Sample validation/testing (exp) study links
1. CFD model validation for hydrogen dispersion: Nice study - http://www.gexcon.com/doc//PDF%20files/Middha_Hansen_Storvilk_HydrogenDispersion_09.pdf
2. Stirred vessel mixing test case study released by ANSYS: http://www.bakker.org/cfm/publications/tn253.pdf
3. Often wind tunnel experiments and studies form a large portion of the CFD testing and validation database: I came across one of these sites
http://ftp.rta.nato.int/public//PubFulltext/RTO/TR/RTO-TR-027///$TR-027-02.pdf
4. How about a CFD evaluation study of wind tunnel flow quality itself !!?
http://sts.bwk.tue.nl/UrbanPhysics/CFD_windtunnel.htm
5. one of the openfoam based WIKI has a site for multiphase activities: http://openfoamwiki.net/index.php/Sig_Multiphase
6. I am no supporter of any particular book / reference..recently had a chance to look at this book ("Validation of Advanced Computational Methods for Multiphase Flow", C2005). It was a nice collection of the test cases (fairly well known to most of us)
http://www.begellhouse.com/books/709c03c830e1b733
I found this article sometime ago on the "general BEST practices guide for numerical accuracy"
http://www.kxcad.net/ansys/ANSYS_CFX/help/help/Reference/CDDDFGCH.html
Coding and implementation is one part of the puzzle. Without validation and testing, no software package is complete. (No wonder so many job availability for validation and testing are on the rise !! Customers want to see more validation reports / testing reports before they award any contract to potential CFD consulting services or the big players)
Make sure whatever you code -----> is properly validated.
Friday, May 6, 2011
CFD's new frontier: OpenFoam
I recently came across this site http://www.cfse.ch/cfse/site/openfoam.php which uses openFoam for several multiphase applications such as free surface VOF modeling of flows around Motor yacht, hydrodynamica analysis of submerged propeller and several other interesting items.
Safe enough to say, the OF users count has swelled quite dramatically over the years. From the interactions I have had with researchers, a lot of them are quite satisfied with the already existing modules (REMEMBER - FREE TO USE) available from OpenFoam installation. Guess what, with every new release the developers keep adding new "foam modules" in every section combustion, multiphase, incompressible/compressible etc..have you checked out the latest release.
I was not quite following the latest release and when I did, I was quite amazed by the amount of additional features OF has incorporated and again "FREE TO USE AND DEVELOP" !!!
Now, several organizations (sometimes I provide consultations) have now resorted to the use of OPENFOAM as their primary investigation tool - giving the clients, specific developmental modules as deliverables. For example, recently I modeled evaporative boiling in cooling water jackets for automotive boiling flow applications and provided source codes as a deliverable. All the client had to do was take this, place it in their directory and compile it.
They built their own manual - indicating what properties has to be varies inclusive of constants and "fudge factors" which we often provide to take into account the dynamics in such multiphase calculations.
Now big interactive GUIs, no fancy JAVA interfaces, simply editing of the file using a word editor - notepad, VIM (linux) and guess what they have modified the "run" file. What an ease !
Some boiling flow simulations using openFoam with VOF with numerical modeling issues is available here for discussion
http://www.csi.tu-darmstadt.de/media/csi/news_1/dbdopenfoamworkshop/kunkelmann_20090407_csi_openfoam_workshop_kunkelmann.pdf
Take a look at a recent plan, http://virtual.vtt.fi/virtual/safir2010/vasenpalkki/finalseminar/Presentations/Thursday/Area_4/NuFoam_SAFIR2010.pdf
that one of the institutes has for Foam two phase solver development. Simply terrific potential they see in this source codes.
Article by Jasak (Foam developer) on the opensource CFD in industry and research is a nice article i suggest reading
http://210.98.5.85/index.php/jnaoe/article/viewFile/24/pdf2-5
with so much wealth and abundancy of information in the web on openfoam - I wonder where is this heading ?? Will ANSYS try "purchasing" openfoam code release and development to retain its monopoly !!>>
Safe enough to say, the OF users count has swelled quite dramatically over the years. From the interactions I have had with researchers, a lot of them are quite satisfied with the already existing modules (REMEMBER - FREE TO USE) available from OpenFoam installation. Guess what, with every new release the developers keep adding new "foam modules" in every section combustion, multiphase, incompressible/compressible etc..have you checked out the latest release.
I was not quite following the latest release and when I did, I was quite amazed by the amount of additional features OF has incorporated and again "FREE TO USE AND DEVELOP" !!!
Now, several organizations (sometimes I provide consultations) have now resorted to the use of OPENFOAM as their primary investigation tool - giving the clients, specific developmental modules as deliverables. For example, recently I modeled evaporative boiling in cooling water jackets for automotive boiling flow applications and provided source codes as a deliverable. All the client had to do was take this, place it in their directory and compile it.
They built their own manual - indicating what properties has to be varies inclusive of constants and "fudge factors" which we often provide to take into account the dynamics in such multiphase calculations.
Now big interactive GUIs, no fancy JAVA interfaces, simply editing of the file using a word editor - notepad, VIM (linux) and guess what they have modified the "run" file. What an ease !
Some boiling flow simulations using openFoam with VOF with numerical modeling issues is available here for discussion
http://www.csi.tu-darmstadt.de/media/csi/news_1/dbdopenfoamworkshop/kunkelmann_20090407_csi_openfoam_workshop_kunkelmann.pdf
Take a look at a recent plan, http://virtual.vtt.fi/virtual/safir2010/vasenpalkki/finalseminar/Presentations/Thursday/Area_4/NuFoam_SAFIR2010.pdf
that one of the institutes has for Foam two phase solver development. Simply terrific potential they see in this source codes.
Article by Jasak (Foam developer) on the opensource CFD in industry and research is a nice article i suggest reading
http://210.98.5.85/index.php/jnaoe/article/viewFile/24/pdf2-5
with so much wealth and abundancy of information in the web on openfoam - I wonder where is this heading ?? Will ANSYS try "purchasing" openfoam code release and development to retain its monopoly !!>>
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