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April 12, 2013, 20:15 
jumpTable: Can someone explain how to use it?

#1 
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PeiYing Hsieh
Join Date: Mar 2009
Posts: 311
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Dear OpenFOAMers,
Could someone explain how to use jumpTable in cyclic fan BC? In the TJunctionFan example, I saw: p { type fan; patchType cyclic; jump uniform 0; value uniform 0; jumpTable polynomial 1((100 0)); }  Does the "polynominal 1((100 0));" mean pressure jump of 100 Pa with 0 velocity? What if I have a 5th order polynominal, like Del_P = a0 + a1*U + a2*U^2 + a3*U^3 + a4*U^4 + a5*U^5. How to specify this? I tried 5((a0 a1 a2 a3 a4 a5)); but, got an error. Thanks! PeiYing 

April 13, 2013, 00:23 

#2 
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Fumiya Nozaki
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Reading the source code(fanFvPatchFields.C), the meaning of "f" dictionary changed from v2.2.0:
To set "Del_P = a0 + a1*U + a2*U^2 + a3*U^3 + a4*U^4 + a5*U^5"
Please correct me if I'm wrong. Hope this helps, Fumiya 

April 13, 2013, 07:27 

#3 
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PeiYing Hsieh
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Hi, Fumiya,
You are a great help! I looked at the source code in fanFvPatch. Could not figure out how to use the polynominal method. So, I ended up using reading the csv method to read in the curve. And yes, in the source code, it looks like it tries to be backward compatible with OF2.1.x, but, when I tried it "f 6(a0 a1 a2 a3 a4 a5)", the case diverged in 4 steps. Maybe there is a bug. PeiYing 

August 13, 2015, 06:42 
HI Hsieh

#4 
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Manjunath Reddy
Join Date: Jun 2013
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What is backward compatible?


August 13, 2015, 07:49 

#5 
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Bruno Santos
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Greetings to all!
@manju819: PeiYing was referring to this piece of code: https://github.com/OpenFOAM/OpenFOAM...chFields.C#L81 Essentially, this boundary condition tries to construct the polynomial that is provided with the "f" option, but reinterpreted into the new data structure. This is the backward compatibility feature. This code doesn't seem to have changed in 2.3.x... I gotta test if this part of the code has a bug or not. edit: I could not find any bugs in the compatibility code. Best regards, Bruno
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Last edited by wyldckat; August 13, 2015 at 09:45. Reason: see "edit:" 

August 17, 2015, 05:42 
Hi Bruno

#6 
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Manjunath Reddy
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Thank you for your reply. I have one more doubt, how does the pressure jump calculated on cyclic patch. For example if I put the pressure jump boundary on cyclic patch as this
Fan1_half0 { type fan; patchType cyclic; jumpTable table ((3.73 524.56)(5.24 429.33)(6.59 244.48)); value uniform 0; } How will it caluclate the jump values on Fan1_half0 and Fan1_half1? Thanks in advance. 

August 17, 2015, 08:30 

#7 
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Bruno Santos
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Quick answer: This is the interpolation table you defined:
Code:
U p 3.73 524.56 5.24 429.33 6.59 244.48 Code:
dp = table(U); What I don't know is if the pressure jump is imposed half to each side or if it's the same on both sides. My guess is that the values are automatically balanced between the two sides, given it's a pair of cyclic patches, therefore the weights on them (the "coeffs" array) will balance it out, i.e. roughly making it half of the value on each side. 

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