The openFoam community is growing much faster than anticipated and researchers are pouring in to implement new models, new methods within the openFoam framework for obtaining research specific results.
Good thing is ...the models generated by a researcher in openFoam can be tracked, understood and bettered by another modeler ..Thanks to the universal template.
Recent updates from the openFOAM world can be obtained from
http://www.openfoam.com/news/
One of the new entries into the OF family is the PIMPLE (PISO/SIMPLE merged version)..Not really a new concept though ..take a look at some old publications
http://cat.inist.fr/?aModele=afficheN&cpsidt=2138118.
Some commercial codes like AVL FIRE and others (i cant seem to recollect) - already have similar implementations - combining PISO/SIMPLE etc - working very well for them. FIRE has a two stage pressure correction method which they robustly use for engine applications (did some research on that ..gives more robust results and very stable)..
Some publications based on this PIMPLE have already started to appear on the recent conferences such as this paper:
1. http://web.univ-ubs.fr/limatb/EG2M/Disc_Seminaire/ECCOMAS-CFD2010/papers/01454.pdf
2. A nice article on PIMPLE based solidification modeling using OPENFOAM. The article has nice details of the implementation part. Download it from the link below
http://dutchopenfoamusers.nl/downloads/Eelco1.pdf
3. Different mesh motion alternatives and related implementation has been reported in a article below
http://www.tfd.chalmers.se/~hani/kurser/OS_CFD_2009/AndreuOliverGonzalez/ProjectReport_Corrected.pdf
The above link has some nice (very nice :)) descriptions of equations on how to implement mesh motion in OF...I certainly loved going over these details ..although most of them are familiar to all of us, little re-read is always helpful.
Also, you can browse, read and download all papers of ECCOMAS 2010, which has lots of OF related papers, from
http://web.univ-ubs.fr/limatb/EG2M/Disc_Seminaire/ECCOMAS-CFD2010/papers/
Monday, March 28, 2011
Wednesday, January 26, 2011
Paper & Publications from Conferences
In a recent post, a fellow CFD user posted the following link to a set of CFD papers presented at the 10th International congress of fluid dynamics in Egypt (16-19 Dec, 2010).
Conference topics included:
1. Aeroacoustics.
2. Aero-elasticity Applications.
3. Air Conditioning Applications.
4 Applied Aerodynamics.
5. Computational Fluid Dynamics.
6. Experimental Fluid Dynamics.
7. Flow Control and Diagnostics.
8. Flow-Induced Vibration.
9. Fluid Mechanics Applications in Bioengineering.
10. Heat Transfer and Fluid Mechanics.
11. High-Speed Flow.
12. Mechatronics Applications.
13. MEMS and Microfluidics Applications.
14. Multiphase and Reacting Flows.
15. Nano Applications.
16. Propulsion.
17. Turbomachinery.
The papers can be downloaded from
http://www.icfdpegypt.org/abs_temp.html
Also, interestingly long time back, I came across the australian CSIRO site (http://www.cfd.com.au) where you can download several conference proceedings involving several CFD applications, methods etc
For ex: Get all conference proceedings papers from the
"The 1st International Conference on CFD in the Mineral & Metal Processing and Power Generation Industries"
from http://www.cfd.com.au/cfd_conf97/index.html
Some of the papers are really good and gives lots of prospects for future research in CFD. They have all the papers from conferences starting 1997 till 2009 (so far).
Conference topics included:
1. Aeroacoustics.
2. Aero-elasticity Applications.
3. Air Conditioning Applications.
4 Applied Aerodynamics.
5. Computational Fluid Dynamics.
6. Experimental Fluid Dynamics.
7. Flow Control and Diagnostics.
8. Flow-Induced Vibration.
9. Fluid Mechanics Applications in Bioengineering.
10. Heat Transfer and Fluid Mechanics.
11. High-Speed Flow.
12. Mechatronics Applications.
13. MEMS and Microfluidics Applications.
14. Multiphase and Reacting Flows.
15. Nano Applications.
16. Propulsion.
17. Turbomachinery.
The papers can be downloaded from
http://www.icfdpegypt.org/abs_temp.html
Also, interestingly long time back, I came across the australian CSIRO site (http://www.cfd.com.au) where you can download several conference proceedings involving several CFD applications, methods etc
For ex: Get all conference proceedings papers from the
"The 1st International Conference on CFD in the Mineral & Metal Processing and Power Generation Industries"
from http://www.cfd.com.au/cfd_conf97/index.html
Some of the papers are really good and gives lots of prospects for future research in CFD. They have all the papers from conferences starting 1997 till 2009 (so far).
Thursday, July 1, 2010
FLUENT LEARNING MODULES LINK
I know I have posted similar posts before: but the website presented below has a comprehensive list of learning modules, progressing from a simple to more complex solution using FLUENT.
https://confluence.cornell.edu/display/SIMULATION/FLUENT+Learning+Modules
Great for teaching undergraduates - course ware or even for understanding new CFD fronts !!
Enjoy !!
https://confluence.cornell.edu/display/SIMULATION/FLUENT+Learning+Modules
Great for teaching undergraduates - course ware or even for understanding new CFD fronts !!
Enjoy !!
Wednesday, April 28, 2010
CFD : Wind Turbine Simulations
There has been quite some interest lately in modeling and simulating wind turbine flow using CFD operations. Thought, may be my simulation work in this concern may be of interest. I have attached my sample work on computing local wind turbine blade characteristics as well as the wake characteristics generated by these rotating blades.
Boundary condition and set up
Front View of the blades (Meshed)
I used the comfortable ;) sliding mesh techniques to run transient simulations of the rotating turbine blades. Turbulence activated using RNG k-e model. Ofcourse, I am carrying out some LES runs now to check out more interesting eddy characteristics. But, fundamental framework on this transient process remains the same.
All work reported here were of incompressible nature. Air was used as the fluid medium. Geometry of the turbine was generated using some earlier available models from literature. Ofcourse, more complicated profiles can be built based on specifications.
Contours plots of vorticity magnitude around the rotating blades - various increasing time instants (a-j)
Movie of vorticity shedding near the rotating blades - used FieldView for post-processing (could have been better ;)
Plots of Velocity vector to show local flow characteristics
Wake Flow Studies
I carried out several tests with increasing the incoming fluid flow velocity, changing the rotational speeds etc and interesting flow modification appeared throughout the domain.
This is just a preliminary post. I will keep adding some more information with respect to these simulations. More so, if you have any comments on the modeling and/or application, kindly let me know.
Boundary condition and set up
Front View of the blades (Meshed)
I used the comfortable ;) sliding mesh techniques to run transient simulations of the rotating turbine blades. Turbulence activated using RNG k-e model. Ofcourse, I am carrying out some LES runs now to check out more interesting eddy characteristics. But, fundamental framework on this transient process remains the same.
All work reported here were of incompressible nature. Air was used as the fluid medium. Geometry of the turbine was generated using some earlier available models from literature. Ofcourse, more complicated profiles can be built based on specifications.
Contours plots of vorticity magnitude around the rotating blades - various increasing time instants (a-j)
Movie of vorticity shedding near the rotating blades - used FieldView for post-processing (could have been better ;)
Plots of Velocity vector to show local flow characteristics
Wake Flow Studies
I carried out several tests with increasing the incoming fluid flow velocity, changing the rotational speeds etc and interesting flow modification appeared throughout the domain.
This is just a preliminary post. I will keep adding some more information with respect to these simulations. More so, if you have any comments on the modeling and/or application, kindly let me know.
Wednesday, February 17, 2010
Eulerian Multi-fluid modeling: Developer and User Perspective
Understanding and implementing a multi-fluid model in any software code is a tedious and strenous process. The complication, not only arises owing to coding the procedure, rather to make sure that the system is stable after being washed with multiple "stablizing" approaches such as treatment of implicit drag terms to indicate a few. Often, CFD vendors have a single route for multiphase solution and it takes different forms based on the approach required: such as VOF, Eulerian or mixture type approaches. So, basically a given multiphase code assumes different formulations for fluxes, source / sink terms and induces the need for coupling (only in eulerian multifluid approach) based on the user specification.
Although, most of the users are not quite interested in the "background coding" involved in the blackbox tool, sometimes it becomes essential that they understand the physical significance of the methodology employed.
For example, let me indicate an off the shelf trick to make your eulerian multi-fluid runs much stable. Increasing the drag terms, involved between the phases, results in higher coupling and hence stable runs. Lowering the interaction terms makes the system (or the involved fluids) decoupled and may pose problems for mass convergence. Well, while writing papers people indicate, "enhancement in convergence was obtained by improving the interaction terms between the fluids" - which essentially a developer would read, the left hand side diagonal terms were made dominant :) !!! Such is the essence of CFD - both the user with a physical representation of the phenomena and the developer in a mathematical state of mind can mingle together talking about the same stuff!!
For those who are interested in the formulation part: I am presenting some nice lectures/notes on multi-fluid formulation.
Ofcourse, if you have any comments on the algorithms or suggest different approaches, please feel free to comment - i would be very interested in getting to know new techniques !
Take a look at this website for a decent understanding of the multi-fluid approach
http://www.tnw.tudelft.nl/live/pagina.jsp?id=abc4209a-4a5f-4a77-9121-54850566f33f〈=en
For detailed understanding of the Multi-fluid approach, one can always lean to the Fluent presentation
www.bakker.org/dartmouth06/engs150/18-eulmp.ppt
Modeling of Gas-fluidized systems require very detailed investigation of the drag formulations (although, people tend to think of it more in a physical manner- the truth is ..such systems are extremely unstable owing to the multiple interaction terms and hence a good implicit approach is required to enhance convergence!)
http://www.wpi.edu/Academics/Depts/CHE/Research/HMTL/CFD_in_CRE_IV/vanderHoef.pdf
http://www.princeton.edu/~jsun/docs/Sun06fb.pdf (Formulations in MFIX explained)
A nice presentation of gas-liquid reactor simulation with multiple bubble size distribution
http://cfdcre5.org/cfdcre5-Petitti.pdf with discussion on moments, breakup and coalescence rates ..definitely something worth investigating..
CFD modeling of particulate flows (from the Stanford institute) http://web.engr.oregonstate.edu/~sva/archive/apte_ARB_2003b.pdf
http://www.stanford.edu/group/ctr/Summer/SP08/4_5_Massot2_new.pdf (turbulent combustion part)
Eulerian models for polydisperse evaporating sprays: http://hal.archives-ouvertes.fr/docs/00/44/98/66/PDF/Kah_etal_Pope_final.pdf
I tend to use the keywords such as polydisperse models, dilute sprays, etc so that if one is searching for these keywords over the web, the blog presented here may be useful in finding some relevant papers.
A very nice use of Eulerian multi-fluid modeling for biological transport:
http://www.personal.psu.edu/rfk102/PUBS/BIOMED2003Paper.pdf
Although, most of the users are not quite interested in the "background coding" involved in the blackbox tool, sometimes it becomes essential that they understand the physical significance of the methodology employed.
For example, let me indicate an off the shelf trick to make your eulerian multi-fluid runs much stable. Increasing the drag terms, involved between the phases, results in higher coupling and hence stable runs. Lowering the interaction terms makes the system (or the involved fluids) decoupled and may pose problems for mass convergence. Well, while writing papers people indicate, "enhancement in convergence was obtained by improving the interaction terms between the fluids" - which essentially a developer would read, the left hand side diagonal terms were made dominant :) !!! Such is the essence of CFD - both the user with a physical representation of the phenomena and the developer in a mathematical state of mind can mingle together talking about the same stuff!!
For those who are interested in the formulation part: I am presenting some nice lectures/notes on multi-fluid formulation.
Ofcourse, if you have any comments on the algorithms or suggest different approaches, please feel free to comment - i would be very interested in getting to know new techniques !
Take a look at this website for a decent understanding of the multi-fluid approach
http://www.tnw.tudelft.nl/live/pagina.jsp?id=abc4209a-4a5f-4a77-9121-54850566f33f〈=en
For detailed understanding of the Multi-fluid approach, one can always lean to the Fluent presentation
www.bakker.org/dartmouth06/engs150/18-eulmp.ppt
Modeling of Gas-fluidized systems require very detailed investigation of the drag formulations (although, people tend to think of it more in a physical manner- the truth is ..such systems are extremely unstable owing to the multiple interaction terms and hence a good implicit approach is required to enhance convergence!)
http://www.wpi.edu/Academics/Depts/CHE/Research/HMTL/CFD_in_CRE_IV/vanderHoef.pdf
http://www.princeton.edu/~jsun/docs/Sun06fb.pdf (Formulations in MFIX explained)
A nice presentation of gas-liquid reactor simulation with multiple bubble size distribution
http://cfdcre5.org/cfdcre5-Petitti.pdf with discussion on moments, breakup and coalescence rates ..definitely something worth investigating..
CFD modeling of particulate flows (from the Stanford institute) http://web.engr.oregonstate.edu/~sva/archive/apte_ARB_2003b.pdf
http://www.stanford.edu/group/ctr/Summer/SP08/4_5_Massot2_new.pdf (turbulent combustion part)
Eulerian models for polydisperse evaporating sprays: http://hal.archives-ouvertes.fr/docs/00/44/98/66/PDF/Kah_etal_Pope_final.pdf
I tend to use the keywords such as polydisperse models, dilute sprays, etc so that if one is searching for these keywords over the web, the blog presented here may be useful in finding some relevant papers.
A very nice use of Eulerian multi-fluid modeling for biological transport:
http://www.personal.psu.edu/rfk102/PUBS/BIOMED2003Paper.pdf
Tuesday, February 16, 2010
CFD Forums
In order to obtain complete control over the "commercial" blackbox codes, it is imperative that users discuss the finer details of the code implementation (user functions) so as to maximize the benefits ..the code has to offer. As most of the readers know, CFD-online has the primary source for many of us. Given that, several other forums such as
Fluent University Forums:
http://university.fluent.com/forum/viewtopic.php?p=385&sid=a4c100c125bf479c72bcc07e6c117432
http://university.fluent.com/forum/viewtopic.php?p=2934&sid=98f99ad4d91f615f7be6fcd74a7665c6
CommentPortals: http://commentportal.com/search/udf-compile-error--cfd-online-discussion-forums
can provide elaborate discussions on certain stuff that may be missing in CFD-online.
I, in fact, strongly recommend Fluent users to become a part of the Fluent University Forum community. Besides getting answers from fellow CFD users, sometimes the developers themselves post results to queries which just makes it perfect ;) - straight from the source. Search for other topics (anything in Fluent) and errors/bugs that you think exists within the code can be discussed here. In fact, this portal serves as a nice forum to let Fluent guys know your exact problems.
Website providing tips for CFD modeling (especially multiphase flows such those using VOF etc) are also very helpful
http://www.cfluid.com/bbs/archiver/?tid-42834.html
I came across this site where manuals for different softwares and discussions pertaining to their usage are available.
http://www.cadfamily.com/downlist/s_115_1.html
Fluent University Forums:
http://university.fluent.com/forum/viewtopic.php?p=385&sid=a4c100c125bf479c72bcc07e6c117432
http://university.fluent.com/forum/viewtopic.php?p=2934&sid=98f99ad4d91f615f7be6fcd74a7665c6
CommentPortals: http://commentportal.com/search/udf-compile-error--cfd-online-discussion-forums
can provide elaborate discussions on certain stuff that may be missing in CFD-online.
I, in fact, strongly recommend Fluent users to become a part of the Fluent University Forum community. Besides getting answers from fellow CFD users, sometimes the developers themselves post results to queries which just makes it perfect ;) - straight from the source. Search for other topics (anything in Fluent) and errors/bugs that you think exists within the code can be discussed here. In fact, this portal serves as a nice forum to let Fluent guys know your exact problems.
Website providing tips for CFD modeling (especially multiphase flows such those using VOF etc) are also very helpful
http://www.cfluid.com/bbs/archiver/?tid-42834.html
I came across this site where manuals for different softwares and discussions pertaining to their usage are available.
http://www.cadfamily.com/downlist/s_115_1.html
Tuesday, February 9, 2010
VOF Modeling / Applications : Sprays / Droplet Breakup-Deformation-Coalescence .....
One the important problems where more academic fellows look to employ multiphase-VOF approach concerns the breakup of droplets (bunch of stuff can be investigated here : effect of shear, liquid/gas density ratios, velocity of impact etc). They keep publishing stuff back and forth so that they can honor their "commitment to publications!" either during tenure period or post-tenure (this time, the grad students are made to kill the problem !)
Anyways, being beaten down time to time or not, droplet simulations is something I have personally grown fond of ..especially the use of VOF in creating almost real droplets is simply artistic nonetheless !From studies on droplets, emerge, more sophisticated studies such as spray breakup, spray impingement problems etc that are of vast interest in real-world applications.
Having said that, it still becomes essential to find lot of literature in this special field so as to improve one's understanding of the phenomena and the applied numerical methods.
In this edition of the blog, I am going to share some of the droplet dynamics (breakup coalescence) studies that I have bookmarked and read over the years. Hopefully, someone may find it useful to read further into these nicely written work.
I came across this nice presentation sometime ago,
http://cfdcre5.org/cfdcre5-Dietsche.pdf
detailing aspects of droplet breakup from an industrial point of view. The presentation infact shows how droplet entering into a matrix of obstacles gets torn apart ! Mechanisms such as "stick and pull", spreading, etc are nicely indicated. Effect of viscosity ratios on the breakup rates are also available.
Dr. Renardy's work in VOF flows is well known. Their group site has a complete list of VOF papers including their PROST model.
http://www.math.vt.edu/people/renardyy/Research/Publications/
All kind of publications dealing with droplet oscillations, shear flow (droplet dynamics), deformation due to strain in both 2D/3D approximation are available for download.
Also, you can find the PROST model here
http://www.ann.jussieu.fr/~frey/papers/stokes/Renardy%20Y.,%20Prost-%20a%20parabolic%20reconstruction%20of%20surface%20tension%20for%20the%20volume-of-fluid%20method.pdf
How could I not include the famous openFoam based VOF studies: (fundamental presentation by Dr. Jasak)
http://powerlab.fsb.hr/ped/kturbo/openfoam/slides/UniDarmstadt_12Jan2005.pdf
Droplet sedimentation simulation using Finite Element - Level Set Methods - interesting one !
http://www.igpm.rwth-aachen.de/Download/reports/reusken/ARpaper55.pdf
Simulation of the dynamics of insoluble surfactant from Univ of Minnesota !
http://static.msi.umn.edu/rreports/2004/291.pdf
The above publication has extensive details of the numerical approach. The modeling includes surface tension force term represented by a linear/non-linear function of surfactant concentration using the continuum surface force (CSF) model. Nice read for developers and new onlookers.
How about DNS of droplets in a closed channel:
http://www.fusion.ucla.edu/neil/Publications/DirectSimulationOfFalling.pdf
The presentation below is litte off from the VOF topic: NEvertheless, you can see the application of VOF in inkJET print heads !!
http://www.coventor.com/pdfs/inkjet_design_for_web.pdf
A study on droplet deformation through a micro-fluidic orifice can be downloaded here.
http://anziamj.austms.org.au/ojs/index.php/ANZIAMJ/article/viewFile/953/791
Some VOF papers using different approaches (other than conventional VOF type)
1. Buoyancy driven droplets simulated using hybrid vof - LEVEL SET approach
http://ame-www.usc.edu/cf/Volterra2009/PROGRAM/PAPERS/Paper-62.pdf
2. Simulations of droplet flows using Lattice Boltzmann approach (just to make sure I do not shun LB approach ;)
http://staff.aist.go.jp/naoki-takada/fedsm2003-45166.pdf
3. A good article on jet breakup using particle method
http://www.nmri.go.jp/act/staff/k_shibata/Paper/SHIBATA_JetBreakup,%20.pdf
Shared Presentation of the Day: http://conferences.npl.co.uk/nmaet/downloads/presentations/costa.pdf
(Nice work VOF methods in Spray modeling !)
Anyways, being beaten down time to time or not, droplet simulations is something I have personally grown fond of ..especially the use of VOF in creating almost real droplets is simply artistic nonetheless !From studies on droplets, emerge, more sophisticated studies such as spray breakup, spray impingement problems etc that are of vast interest in real-world applications.
Having said that, it still becomes essential to find lot of literature in this special field so as to improve one's understanding of the phenomena and the applied numerical methods.
In this edition of the blog, I am going to share some of the droplet dynamics (breakup coalescence) studies that I have bookmarked and read over the years. Hopefully, someone may find it useful to read further into these nicely written work.
I came across this nice presentation sometime ago,
http://cfdcre5.org/cfdcre5-Dietsche.pdf
detailing aspects of droplet breakup from an industrial point of view. The presentation infact shows how droplet entering into a matrix of obstacles gets torn apart ! Mechanisms such as "stick and pull", spreading, etc are nicely indicated. Effect of viscosity ratios on the breakup rates are also available.
Dr. Renardy's work in VOF flows is well known. Their group site has a complete list of VOF papers including their PROST model.
http://www.math.vt.edu/people/renardyy/Research/Publications/
All kind of publications dealing with droplet oscillations, shear flow (droplet dynamics), deformation due to strain in both 2D/3D approximation are available for download.
Also, you can find the PROST model here
http://www.ann.jussieu.fr/~frey/papers/stokes/Renardy%20Y.,%20Prost-%20a%20parabolic%20reconstruction%20of%20surface%20tension%20for%20the%20volume-of-fluid%20method.pdf
How could I not include the famous openFoam based VOF studies: (fundamental presentation by Dr. Jasak)
http://powerlab.fsb.hr/ped/kturbo/openfoam/slides/UniDarmstadt_12Jan2005.pdf
Droplet sedimentation simulation using Finite Element - Level Set Methods - interesting one !
http://www.igpm.rwth-aachen.de/Download/reports/reusken/ARpaper55.pdf
Simulation of the dynamics of insoluble surfactant from Univ of Minnesota !
http://static.msi.umn.edu/rreports/2004/291.pdf
The above publication has extensive details of the numerical approach. The modeling includes surface tension force term represented by a linear/non-linear function of surfactant concentration using the continuum surface force (CSF) model. Nice read for developers and new onlookers.
How about DNS of droplets in a closed channel:
http://www.fusion.ucla.edu/neil/Publications/DirectSimulationOfFalling.pdf
The presentation below is litte off from the VOF topic: NEvertheless, you can see the application of VOF in inkJET print heads !!
http://www.coventor.com/pdfs/inkjet_design_for_web.pdf
A study on droplet deformation through a micro-fluidic orifice can be downloaded here.
http://anziamj.austms.org.au/ojs/index.php/ANZIAMJ/article/viewFile/953/791
Some VOF papers using different approaches (other than conventional VOF type)
1. Buoyancy driven droplets simulated using hybrid vof - LEVEL SET approach
http://ame-www.usc.edu/cf/Volterra2009/PROGRAM/PAPERS/Paper-62.pdf
2. Simulations of droplet flows using Lattice Boltzmann approach (just to make sure I do not shun LB approach ;)
http://staff.aist.go.jp/naoki-takada/fedsm2003-45166.pdf
3. A good article on jet breakup using particle method
http://www.nmri.go.jp/act/staff/k_shibata/Paper/SHIBATA_JetBreakup,%20.pdf
Shared Presentation of the Day: http://conferences.npl.co.uk/nmaet/downloads/presentations/costa.pdf
(Nice work VOF methods in Spray modeling !)
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