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-   -   how to find the maximum vorticity and streamfunction in driven caivty (https://www.cfd-online.com/Forums/main/123423-how-find-maximum-vorticity-streamfunction-driven-caivty.html)

 ztdep September 12, 2013 09:36

how to find the maximum vorticity and streamfunction in driven caivty

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 September 12, 2013 15:34

 ztdep September 12, 2013 21:51

Quote:
 Originally Posted by immortality (Post 451400) did you find the answer?
what is the meaning?

 FMDenaro September 13, 2013 03:08

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

 ztdep September 14, 2013 09:28

Quote:
 Originally Posted by FMDenaro (Post 451462) 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?

 leflix September 15, 2013 14:55

Quote:
 Originally Posted by ztdep (Post 451667) 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

 ztdep September 15, 2013 21:05

Quote:
 Originally Posted by leflix (Post 451840) 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.

 agd September 15, 2013 21:40

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.

 agd September 15, 2013 22:18

But even that will be grid dependent if the underlying solution is grid dependent.

 FMDenaro September 16, 2013 02:54

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

 immortality September 16, 2013 06:12

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).

 kaveh fathi September 16, 2013 15:17

open foam

hi everybody
I have run a program but the software shows some error .if you can help me I will send errors for you.:)

 immortality September 16, 2013 17:48

hi
whats your problem?which university are you?

 kaveh fathi September 18, 2013 04:15

openFoam

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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