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how to find the maximum vorticity and streamfunction in driven caivty

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Old   September 12, 2013, 09:36
Default how to find the maximum vorticity and streamfunction in driven caivty
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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
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Old   September 12, 2013, 15:34
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did you find the answer?
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Old   September 12, 2013, 21:51
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did you find the answer?
what is the meaning?
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Old   September 13, 2013, 03:08
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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
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Old   September 14, 2013, 09:28
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Originally Posted by FMDenaro View Post
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?
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Old   September 15, 2013, 14:55
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Quote:
Originally Posted by ztdep View Post
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
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Old   September 15, 2013, 21:05
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Originally Posted by leflix View Post
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.
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Old   September 15, 2013, 21:40
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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.
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Old   September 15, 2013, 22:18
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But even that will be grid dependent if the underlying solution is grid dependent.
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Old   September 16, 2013, 02:54
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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
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Old   September 16, 2013, 06:12
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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).
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Old   September 16, 2013, 15:17
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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.
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Old   September 16, 2013, 17:48
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hi
whats your problem?which university are you?
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Old   September 18, 2013, 04:15
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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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