# how to find the maximum vorticity and streamfunction in driven caivty

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 September 12, 2013, 09:36 how to find the maximum vorticity and streamfunction in driven caivty #1 Senior Member     p ding Join Date: Mar 2009 Posts: 337 Rep Power: 11 Dear friends: i solved the 2D lid driven cavity problem using SIMPLE algorithm. could you please tell me how to obtain the maximum vorticity and stream function in the flow field. thanks immortality likes this.

 September 12, 2013, 15:34 #2 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 20 did you find the answer? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

September 12, 2013, 21:51
#3
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p ding
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Quote:
 Originally Posted by immortality did you find the answer?
what is the meaning?

 September 13, 2013, 03:08 #4 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 3,751 Rep Power: 41 At steady state, compute the vorticity from your velocity field and solve the elliptic equation Lap (Psi) = vorticity. This way you get both functions and all the values you need immortality likes this.

September 14, 2013, 09:28
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p ding
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Quote:
 Originally Posted by FMDenaro At steady state, compute the vorticity from your velocity field and solve the elliptic equation Lap (Psi) = vorticity. This way you get both functions and all the values you need
thank you . i can obtain the whole field of them. but my problem is to find the maximum values so as to compare it with the benchmark solutions in the public paper. Since we only have the field on grid points. then how to find the maximum value?

September 15, 2013, 14:55
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Quote:
 Originally Posted by ztdep thank you . i can obtain the whole field of them. but my problem is to find the maximum values so as to compare it with the benchmark solutions in the public paper. Since we only have the field on grid points. then how to find the maximum value?

Let's imagine your are in 2D and vorticity is stored in an array VOR(NI,NJ).

VORMAX=VOR(1,1)

DO J=1,NJ
DO I=1,NI

IF ( VOR(I,J).GT.VORMAX ) VORMAX = VOR(I,J)

END DO
END DO

assume fortran coding

September 15, 2013, 21:05
#7
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p ding
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Quote:
 Originally Posted by leflix Let's imagine your are in 2D and vorticity is stored in an array VOR(NI,NJ). VORMAX=VOR(1,1) DO J=1,NJ DO I=1,NI IF ( VOR(I,J).GT.VORMAX ) VORMAX = VOR(I,J) END DO END DO assume fortran coding
thank you , but i can not fully agree with you. in this way, the maximum value will depend on the mesh density.

 September 15, 2013, 21:40 #8 Senior Member   Join Date: Jul 2009 Posts: 247 Rep Power: 12 Establish a grid-independent solution. Otherwise any approach you follow will depend on the grid, whether you use an interpolation method or simply find the max over the grid.

 September 15, 2013, 22:18 #9 Senior Member   Join Date: Jul 2009 Posts: 247 Rep Power: 12 But even that will be grid dependent if the underlying solution is grid dependent.

 September 16, 2013, 02:54 #10 Senior Member   Filippo Maria Denaro Join Date: Jul 2010 Posts: 3,751 Rep Power: 41 leflix is right, just add the i,j values where the maximum is obtained. What you ask for is simply wrong. In a numerical solution nothing else exists but the grid value. This is established by the Nyquist theorem. When you want to compute some extra-grid value, is common to use some interpolation to reconstruct a continous function. But the values you obtain are somehow arbitrarily, depending on the order of the polynomial reconstruction. Therefore, just use the grid value, they are meaningfull of your solution

September 16, 2013, 06:12
#11
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Ehsan
Join Date: Oct 2012
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Hi Ztdep
Quote:
 thank you , but i can not fully agree with you. in this way, the maximum value will depend on the mesh density.
why you say that it will be grid dependent?if the main solution be grid independent,then vorticity values will be independent and you can use the code like a postProcessing utility for obtaining maximum vortivity(at least by theory).
__________________
Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King.
To Be or Not To Be,Thats the Question!
The Only Stupid Question Is the One that Goes Unasked.

 September 16, 2013, 15:17 open foam #12 New Member   kaveh fathi Join Date: Aug 2013 Posts: 2 Rep Power: 0 hi everybody can you help me about openFoam ?please I have run a program but the software shows some error .if you can help me I will send errors for you.

 September 16, 2013, 17:48 #13 Senior Member     Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,209 Rep Power: 20 hi whats your problem?which university are you? __________________ Injustice Anywhere is a Threat for Justice Everywhere.Martin Luther King. To Be or Not To Be,Thats the Question! The Only Stupid Question Is the One that Goes Unasked.

 September 18, 2013, 04:15 openFoam #14 New Member   kaveh fathi Join Date: Aug 2013 Posts: 2 Rep Power: 0 hi I am in razi university from kermanshah. I am working with openfoam I am going to analyse ac cavity .my solver is boussinesqsimple .when I run the program there is some error in fvslution(include solver for pressuer & tempreture & velocity and SIMPLE solver) file .I have copied this file from another exaxmple without any changing. I should be say that the software reads constant & 0 files.

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