how to find the maximum vorticity and streamfunction in driven caivty

ztdep · September 12, 2013, 09:36

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

did you find the answer?

ztdep · September 12, 2013, 21:51

Quote:

Originally Posted by immortality

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

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

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

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

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.

immortality · September 16, 2013, 17:48

hi
whats your problem?which university are you?

kaveh fathi · September 18, 2013, 04:15

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.

September 12, 2013, 09:36	how to find the maximum vorticity and streamfunction in driven caivty	#1
ztdep Senior Member p ding Join Date: Mar 2009 Posts: 427 Rep Power: 19	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
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	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 13, 2013, 03:08		#4
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	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 16, 2013, 15:17	open foam	#12
kaveh fathi 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
immortality Senior Member Ehsan Join Date: Oct 2012 Location: Iran Posts: 2,208 Rep Power: 26	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 15, 2013, 21:40		#8
agd Senior Member Join Date: Jul 2009 Posts: 354 Rep Power: 18	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
agd Senior Member Join Date: Jul 2009 Posts: 354 Rep Power: 18	But even that will be grid dependent if the underlying solution is grid dependent.

September 16, 2013, 02:54		#10
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,768 Rep Power: 71	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 18, 2013, 04:15	openFoam	#14
kaveh fathi 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.