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March 24, 2014, 08:55 |
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#41 |
Member
Sergey
Join Date: Nov 2013
Posts: 87
Rep Power: 12 |
I have OF version 2.2.
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March 27, 2014, 16:38 |
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#42 | |
Senior Member
Derek Mitchell
Join Date: Mar 2014
Location: UK, Reading
Posts: 172
Rep Power: 13 |
Quote:
changing Code:
neighbourFieldName T; Code:
Tnbr T; and adding Code:
laplacian(rhorAUf,p_rgh) Gauss linear uncorrected; |
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April 20, 2014, 15:59 |
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#43 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,982
Blog Entries: 45
Rep Power: 128 |
Greetings Derek,
Many thanks for the feedback! I've uploaded the adapted tutorial for OpenFOAM 2.3, with some additional changes, based on the changes made on the OpenFOAM tutorials: http://openfoamwiki.net/index.php/Ge..._-_planeWall2D Best regards, Bruno
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April 21, 2014, 12:27 |
Heat transfer between two solids
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#44 |
Senior Member
Mohammad Shakil Ahmmed
Join Date: Oct 2012
Location: AUS
Posts: 137
Rep Power: 15 |
Hi Foamer,
I have to solve a problem of heat transfer between two solids. I have to solve the transient heat conduction equation for both of the solids with a volumetric heat source. Now, I'm wondering about how to do this for the conjugate heat transfer problem in OpenFOAM. Specially which boundary condition will be good to use at the interface of the two solids. Please advice me. cheers shakil |
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October 30, 2014, 12:10 |
Questions on the panelWall2D
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#45 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
hi, everyone. I'm trying to simulate a similar problem with the panelWall2D.I have learned the OpenFoam for three days by reading the 2.3.0 user guide now. I have the following questions:
1.Am I supposed to write up every single file in the example to simulate this question? That's a lot of them! Are there any files are generated automatically? 2.Since the question is looking at a 'air-wall-air' region, why there is only one bloke in the blockMeshDict? My first guess was three. 3. I can roughly understand what each file tries to define, but not quite sure how these are coupled with each other. Is there any document clarifies how I should allocate my question into the files. 4. Is there any file that defines the question that has been solve with the panelWall2D. It's a little bit confusing with only the openfoam file. Thanks a lot |
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November 1, 2014, 16:37 |
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#46 | |||||
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,982
Blog Entries: 45
Rep Power: 128 |
Greetings a19910112a and welcome to the forum!
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Keep in mind that OpenFOAM is mostly a "DIY - Do-It-Yourself" kind of software toolbox, which is why it's so... manual Read (again) the first chapter of the User Guide and you'll understand what I mean: http://www.openfoam.org/docs/user/userch1.php But if you're looking for more interactive ways of dealing with OpenFOAM, check this wiki page: http://openfoamwiki.net/index.php/GUI Quote:
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Best regards, Bruno
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November 3, 2014, 08:48 |
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#47 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
hi,wyldckat.
Thank you so much for you reply.I have looked through the wall2D example, and understand most of it now. The problem I'm trying to simulated is similar to it: I need to replace the bottom air with some matter that can generate heat, and the top air with liquid coolant (e.g. water,sodium). This is more like the example 3.7 described in the Fundamentals of Heat and Mass Transfer book (http://www.ualberta.ca/~seyedsha/Fun...-Incropera.pdf). Is there any Foam example on this? I have several questions on this problem: 1. Do you think I can still use the chtMultiRegionSimpleFoam solver for this question? If not can you suggest one? (my main concern is that the solver is designed for compressible fluid, isn't it? In addition to that, a heat source is added) 2. The wall2D example is a natural convection or half-natural convection problem to me (I'm not quite sure about this), so that factors like pressure and gravity may matter. My case will be forced convection, therefore I think the factors such as gravity will not matter any more. How should I eliminate them from the code? 3. It seems that how to define the changeDictionaryDict file is not described in the official User guide, is there any instructive documents on this? question on Wall2D example: 4. What is the alternative way to run the ALLRUN file? As my ssh server does not allow this kind of script to run. Thanks a lot. Last edited by a19910112a; November 3, 2014 at 14:16. |
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November 3, 2014, 14:08 |
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#48 | ||||
Senior Member
Alex
Join Date: Oct 2013
Posts: 337
Rep Power: 22 |
Hi man/woman with a weird name!
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You're welcome! Hope it helps a little... Regards, Alex
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Web site where I present my Master's Thesis: foamingtime.wordpress.com The case I talk about in this site was solved with chtMultiRegionSimpleFoam solver and involves radiation. Some basic tutorials are also resolved step by step in the web. If you are interested in these matters, you are invited to come in! |
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November 4, 2014, 08:58 |
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#49 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
hey,Alex. Thanks for your reply. I have the following ideas on your answer:
Question 2: You mentioned that I could change the gravity in the g file. I knew that,. But what if the gravity is not a factor I will need to consider in my situation? I simply set it to 0? Question 3: That answer is very helpful. Do you have any ideas on how to swap the bottom air area with a heat generating area? I saw people were talking about adding a fvOptions file, is that right? What should the fvOptions file define? This is also not described in the user guide. In addition, since there are a lot of useful functions of openFOAM is not mentioned in the user guide, how did you learn about them? And do you know if there is a tutorial that is similar to my case? It seems to be a very common situation in heat transferring. Thanks a lot. Zech |
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November 4, 2014, 09:53 |
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#50 | ||||
Senior Member
Alex
Join Date: Oct 2013
Posts: 337
Rep Power: 22 |
Hey, R2D2 friend.
You're welcome. Quote:
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You're welcome. Regards, Alex
__________________
Web site where I present my Master's Thesis: foamingtime.wordpress.com The case I talk about in this site was solved with chtMultiRegionSimpleFoam solver and involves radiation. Some basic tutorials are also resolved step by step in the web. If you are interested in these matters, you are invited to come in! |
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November 5, 2014, 13:07 |
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#51 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
hey, one quick question:
I know that, in the wall2D example, the changeDictionaryDict is used for defining the boundary functions. But what do the expressions such as "topAir_to_.*" and "ILambda.*" mean? I guess ".*" could mean "rest of them" or "those that are not defined",but cannot even guess that. And p and p_rgh are given same values. somebody told me that P_rgh=p- rho*g*h. If that is true, then rho*g*h some how becomes 0? It's also confusing that how the value of epsilon and k are calculated according to equation 2.8 and 2.9 in the user guide. Last edited by a19910112a; November 5, 2014 at 14:46. |
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December 4, 2014, 05:39 |
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#52 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
Dear All,
I find a problem will the planeWall2D case. I drew the temperature profile of the bottom line of the topAir area and found a curve rather than a straight line as I expected. I looked at the case description. Because the wall and fluids are infinity that should not be the case. I also checked all the temperature boundary conditions that are defined in both 0 and system folders. Also I think the temperature of the topAir should in crease along the direction it flows as the bottom air keeps transferring heat to it along the direction. However, the temperature profile shows the temperature is constant. This should also be a problem. Anyone knows what's going on? Last edited by a19910112a; December 8, 2014 at 14:52. |
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December 8, 2014, 16:27 |
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#53 | |||||||
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,982
Blog Entries: 45
Rep Power: 128 |
Greetings to all!
@a19910112a: To start off, please do take some time to add new information to the tutorial on the wiki, specially after checking with people here on the forum what's right or not Quote:
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This to say that you are correct in pointing out that the values seem very suspicious. Nonetheless, there is a trick being used in the "changeDictionaryDict" file that isn't very well explained, but that it's implied by the settings. For example:
In addition, this: Code:
internalField uniform 1e5; Quote:
I know I wrote something about this sometime ago... OK, after a quick search, this thread seems to be detailed enough: http://www.cfd-online.com/Forums/ope...on-values.html Quote:
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There it's written this: http://openfoamwiki.net/index.php/Ge...sted_Exercises Quote:
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Yes, I do: you didn't fully read into all of the (implied and explicit) details of this tutorial/example This tutorial explicitly states not being complete right in the introduction section and essentially tries to give the reader the sense of "this is only a start and every single detail is important, because it's not explained in every single detail"! And that you should do the mentioned exercises, in order to gain more experience on this type of simulation Best regards, Bruno
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December 9, 2014, 05:11 |
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#54 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
Thanks for your answer, Bruno.
Well I think the 'the case is not infinite' might be able to explain why the curve appears and therefore the temperature profile along the same line in the wall and topAir area doesn't match. But, it seems that it could not explain why the temperature doesn't increase along the line: infinite or not, heat is accumulated along the x direction, without changing in mass and heat capacity, the temperature should increase anyway. I have done the step mentioned in the exercise ( change the boundary condition to cyclic and set the wall to be infinite long). There seems nothing has changed with the temperature profile. The 'curve' is still there. I cannot upload the case file here, as I don't really know how to properly set the cyclic boundary conditions using the changeDictionaryDict, therefore many setting steps are done manually. Every time I try to do that, I get a floating point exception error. Waiting for more answers... Thanks and Wishes Zech Last edited by a19910112a; December 9, 2014 at 16:07. |
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December 10, 2014, 16:23 |
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#55 | ||
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,982
Blog Entries: 45
Rep Power: 128 |
Quick answers:
Quote:
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The idea is to leave the case folder as clean as the one provided on the wiki and then compress the whole folder to a "zip" or "tar.gz" file. As long as the file is smaller than 100kB, the forum should accept it. |
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December 11, 2014, 07:56 |
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#56 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
Hello,Bruno. Thanks for answering again.
Can you please clarify what should be set to be infinite for the exercise? Just the wall or the flows as well? If it's the flows, how could you define the boundary as cyclic and fixed inlet values at the same time? |
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December 13, 2014, 14:13 |
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#57 |
New Member
zech
Join Date: Oct 2014
Location: Cambridge,England
Posts: 22
Rep Power: 12 |
Hi,Bruno. I know that you will not be able to look at the posts recently, but I will just post things I did related to the question here.
With the previous results, I thought: 'fine! If that problem is still too complex for me, I will try an even simpler one'. Therefore I wrote up a case uses buoyantBoussinesqPimpleFoam to solve only the topAir area (by setting a fixed T gradient at the topAir_bottom boundary). As the problem is not with quantity, I disregarded the thermal properties numbers and used the files copied directly from the solver's tutorial case's files directly and even a different sized block was defined. The result is that I get the exactly same two problems: 1. The drops at the edges (the curved temperature profile) along the top_air bottom boundary. 2. Temperature does not increase along the flow direction. I did not use the cyclic boundary as the question in post #56 is not answered yet. Please find the attachments for more details. |
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December 13, 2014, 16:05 |
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#58 | ||||
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,982
Blog Entries: 45
Rep Power: 128 |
Hi Zech,
Quote:
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To turn this into an infinite wall, either:Nice... I inverted a sentence as if it was an equation But since you asked, the idea behind that sentence was as follows:
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Sorry to say that using that solver is not simple enough "buoyant Boussinesq" is an approximation for incompressible flow: http://en.wikipedia.org/wiki/Boussin...%28buoyancy%29 In other words: it won't always work as expected, specially if you work outside of the operational temperature zone. It's preferable if you use buoyantPimpleFoam or buoyantSimpleFoam. (FYI: I use bold for telling apart solver names from text.) Quote:
What I can say right now and which I only now noticed that I should have emphasized once again (I think I wrote this sometime ago on this very same thread): In order to fully understand what's happening with these solvers and to properly validate if they are working correctly, is to find the analytical solution for this problem. In other words, you need to find the function of temperature dependant on the distance to the wall. This requires that you study chapter 3 from the book Fundamentals of Heat and Mass Transfer by Frank P. Incropera et. al, or a similar book. Back when I wrote this particular wiki page, I did try to find a similar tutorial online that explained this in detail, namely the analytical part, but I wasn't able to find one If you can ask one of your teachers for another example of this, please let us know about it! By the way, at the end of the wiki page for the "Plane Wall 2D" are links to a project that used this wiki page as a basis. The author of that report has some more details on this topic and also shows a similar temperature distortion near the outlet. Which reminds me: I originally was thinking that you're aware of what a "boundary layer" is. If you aren't aware of what it is, here's some interesting reading material: http://en.wikipedia.org/wiki/Boundary_layer Best regards, Bruno |
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January 1, 2015, 18:35 |
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#59 |
Retired Super Moderator
Bruno Santos
Join Date: Mar 2009
Location: Lisbon, Portugal
Posts: 10,982
Blog Entries: 45
Rep Power: 128 |
Greetings to all!
I had this on my to-do list for sometime now and over a period of 10 hours today I worked on and off on the tutorial page discussed on this thread, namely this tutorial: http://openfoamwiki.net/index.php/Ge..._-_planeWall2D I've improved a bit the case description, by adding images and the equivalent diagram. But the bulk of the additions were by adding the new subsection "2.5 Understanding the physics", where most of the topics addressed in the past few posts have been compiled here for a better understanding of what's going on. In addition, I've emphasized in the introduction that this tutorial is not something ready to be used as a practical case. It's only something to start with and to begin carefully diagnosing one step at a time what each detail really means. Unfortunately I'm not willing to spend much more time on this in the coming 6 or so months, because in these 10 hours that passed today, I wanted to also have been able to answer a lot of the questions that are on my to-do list and could not do it, because I was busy with this tutorial... and some of those questions have been left unanswered for some 6 months already oh well... This to say: if people want this tutorial to be better, please study this in more detail, test things and contribute to the wiki page as well! Oh, and Happy New Year to everyone as well! Best regards, Bruno
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January 20, 2015, 09:29 |
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#60 |
Senior Member
Paritosh Vasava
Join Date: Oct 2012
Location: Lappeenranta, Finland
Posts: 732
Rep Power: 23 |
I noticed that many people are having problems with the cht*.* solvers. So I would like to share my experience and how I overcame it. I am not sure if it works for everyone but you could try this.
I have been trying heat-exchanger example of my own with chtMultiRegionSimpleFoam. For all my attempts my cases use to diverge after few iteration citing an abnormally high temperature as an excuse. The transient solver chtMultiRegionFoam worked quite nicely for the same example. But it was very slow. At one point I lost my patience and decided to switch back to the steady state solver. After switching the steady state solver worked nicely without any problems. I think the solution from the transient solver provided a better initial guess for the steady-state solver. Do comment if you believe that I am doing something wrong or something in a wrong way. |
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Tags |
cht, solid-fluid interface |
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