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November 14, 2019, 19:01 |
Darcy-Forchheimer Online Calculator
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#1 |
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Tobias Holzmann
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Hi all,
I just want to inform you, that I implemented an Darcy-Forchheimer Calculator on my website. It is not yet finished and I have to check the results but the next days I will finish it. Nevertheless, the first indications seems to work fine. https://holzmann-cfd.com/community/b...cy-forchheimer
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Keep foaming, Tobias Holzmann Last edited by Tobi; June 22, 2020 at 03:30. |
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July 24, 2022, 07:17 |
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#2 |
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Matej Tomić
Join Date: Jul 2022
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Hello Tobias,
I checked out your calculator tool for the Darcy-Forchheimer coefficients. I am unable to obtain the Darcy contribution identical to your calculator, for a 1D case. I am trying to model a heat exchanger with a certain porosity. It would be nice to see how your tool calculates the Darcy contribution. Regards, Matej |
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August 2, 2022, 08:56 |
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#3 |
Super Moderator
Tobias Holzmann
Join Date: Oct 2010
Location: Bad Wörishofen
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Its still crap and buggy. I had not time to check everything in detail.
Matej = Matej Forman? So its my colleague. Do you have the calculation base from him? (community@holzmann-cfd.com). Otherwise you can tell me the material-name and I can check it myself. Thanks, Tobi
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Keep foaming, Tobias Holzmann |
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August 30, 2022, 06:18 |
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#4 |
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Matej Tomić
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Hello Tobi,
Funny coincidence, although I must state that I am in no way, shape or form affiliated with Matej Forman. Inspired by your calculator tool, I made a similar one (only with the help of MATLAB). In order to compare the results with your calculator tool, please use the following info: When inserting aforementioned inputs into your calculator, the Darcy contribution output differs severely.
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Regards, Matej |
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September 2, 2022, 16:57 |
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#5 |
Super Moderator
Tobias Holzmann
Join Date: Oct 2010
Location: Bad Wörishofen
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Hey. Nice and thanks for your feedback.
Using your darcy and forchheimer values by using the equation given on my website (first one right hand side: https://holzmann-cfd.com/community/b...cy-forchheimer), we end up with the graph attached:
dp = (D*U+F*U^2)*dx using dx = 0.073 m So with your extreme linear contribution, its clear that you will get such an offset. However, my curve is not fitting too good either. Shame on me that I still have that buggy guy available.
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Keep foaming, Tobias Holzmann |
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September 3, 2022, 10:12 |
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#6 |
New Member
Matej Tomić
Join Date: Jul 2022
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Hello Tobi,
Thanks for taking time and looking into this topic. The deviation of the Forchheimer contribution is self-explanatory, as your tool only takes into account two data points. Therefore, the curve fit is of lower fidelity. However, I think that there is some underlying mystery about the Darcy contribution. If we assume that the , then the Darcy and Forchheimer contributions are determined in the following manner: Just by looking at the expression for the Darcy contribution, we can note that in the case of air (dynamic viscosity in the vicinity of 1.73e-5 Pa s) that the Darcy contribution should be a rather large number. So to return to the actual point of my question, how does your tool determine the Darcy contribution?
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Regards, Matej |
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September 3, 2022, 15:22 |
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#7 |
Super Moderator
Tobias Holzmann
Join Date: Oct 2010
Location: Bad Wörishofen
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The main problem in the whole calculation is that I need (or we need) to avoid negative numbers as they are treated differently by OpenFOAM (a negative number means blockage).
I second your statement and if you only take the Darcy-Calculation into account (in my tool), you will get D to be around 119246891. Hence, a very large number as you have. My tool is doing some magic No, its simply some derivation - need to recheck but its in the javascript that you can checkout manually if you go through my source-code of the website (view-source:https://holzmann-cfd.com/modules/mod...Forchheimer.js) Code:
/* OLD var f = parseFloat(dp1)/parseFloat(dx) /( ( ( parseFloat(dp1)*parseFloat(u2)*parseFloat(u2) -parseFloat(dp2)*parseFloat(u1)*parseFloat(u1) ) / ( parseFloat(dp2)*parseFloat(u1) -parseFloat(dp1)*parseFloat(u2) ) )*u1+parseFloat(u1) ); var r = ( parseFloat(dp2)/parseFloat(dx) -parseFloat(f)*parseFloat(u2)*parseFloat(u2) )/parseFloat(u2); */ var f = ( parseFloat(dp2)*parseFloat(u1)*parseFloat(dx) - parseFloat(dp1)*parseFloat(u2)*parseFloat(dx) ) / ( (-1 * parseFloat(u1)*parseFloat(dx)*parseFloat(u2)*parseFloat(dx)) + (parseFloat(u2)*parseFloat(u2)*parseFloat(dx)*parseFloat(dx)*parseFloat(u1)) ); var r = ( parseFloat(dp1) - parseFloat(f)*parseFloat(u1)*parseFloat(dx) ) / ( parseFloat(u1)*parseFloat(dx) ); // 10 % more than the given datapoint var largerU = 0; var largerdp = 0; if (parseFloat(dp1) > parseFloat(dp2)) { largerdp = dp1 } else { largerdp = dp2; } if (parseFloat(u1) > parseFloat(u2)) { largerU = u1 } else { largerU = u2; } xGiven = largerU; yGiven = largerdp; console.log("xGiven = " + xGiven); console.log("yGiven = " + yGiven); xTotal = xGiven * 1.1; deltax = xTotal / 20; var i; for (i = 0; i < 50; i++) { xValue.push(i*deltax); yValue.push(r*i*deltax*dx+f*(i*deltax)*(i*deltax)*dx); } }
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Keep foaming, Tobias Holzmann |
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May 11, 2023, 06:58 |
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#8 | |
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Markus Bähner
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Quote:
Hey Tobi, first of all, thanks for making your contributions and the tool available to us all! I just checked out the source code, since i was confused comparing the online calculators small result for the darcy contribution with the very large value i came up with in my own calculations. In Line 397 of the code the coefficients are calculated as: D.value = r*mu.value; F.value = 2*f/rho.value; Isn't there a little mistake here? r gets multiplied by mu, yet per definition the Darcy coefficient is: D = r/mu as Matej stated above. F seems correct to me. Or is this the "magic" you speak of? Im not very experienced with Porous zones in OpenFOAM so please let me know if i am missing anything! Best regards, Markus |
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May 11, 2023, 12:59 |
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#9 |
Super Moderator
Tobias Holzmann
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Hey Markus,
you are excellent. I love people who are investigating into the code and know how to get to the simple javascript. (EDIT: I saw that I posted the link - but anyway - nice that you checked it). I agree - as it is already postulated on my website - D = r / mu. In the code I have D = r * mu for the Darcy-Forchheimer calculation. We also see that the pure Darcy calculation is correct hence, for any reason, I made a mistake here. Thanks for your hint and investigation. Code is already corrected. Tobi
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Keep foaming, Tobias Holzmann |
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May 11, 2023, 17:38 |
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#10 |
New Member
Markus Bähner
Join Date: May 2023
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Stuff like this happens to me all the time - youre a legend for already having the corrected one up and running.
Good yard, Markus |
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May 24, 2023, 12:24 |
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#12 |
New Member
Markus Bähner
Join Date: May 2023
Posts: 4
Rep Power: 7 |
Hey,
scusi for the late reply. Up to that point i hadnt even set up my porous model. However, initial tests with the coefficients seem to produce results which are in the expected ball park. At a later time, i will need to check against some velocity measurements of the prototype to see how far we are off. Cheers |
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