[Nek5000-users] Stream function

Fri Jun 29 03:47:01 CDT 2018

Hi Hannah,

I tried to implement the streamfunction as well (for a 2D cylinder flow) 
and it would appear that, doing naïvely, the tmask is set to zero 
everywhere. Hence, when rhs * tmask is computed in the hmholtz 
subroutine, rhs is set to zero everywhere and it then makes sense that 
the returned streamfunction is zero everywhere as well.

Not sure how to do fix this properly though. Any help would be 
appreciated indeed :)

++
JC

On 06/28/2018 09:41 PM, nek5000-users at lists.mcs.anl.gov wrote:
> Hi Philipp,
>
> Thanks very much for your comments.  Yes, the delta* works only for the parallel plate.
>
> The streamfunction computation with the Blasius example is still not working. I suspect I am not using the correct mask (vmult /tmult, imsh as well).
>
> Using the Blasius example, v1mask, vmult (imsh = 1), I dumped the streamfuntion to the temperature field. However, it only contains negative values and does not look physical (I pasted userchk below).
>
> Another Nek Example, “mv_wall”, computes the streamfunction from the Possison equation using vorticity. It uses tmask, tmult, and imsh = 2.
>
> I tried implementing what was done in the “mv_wall” example in the Blasius example, but the computed streamfunction is zero everywhere.
>
> Any ideas what I might be doing wrong?
>
> Any advice would be appreciated!
>
> Thanks again,
>
> Hannah
>
> c-----------------------------------------------------------------------
>        subroutine userchk
>        include 'SIZE'
>        include 'TOTAL'
>
>        common /myblas/ ub(lx1,ly1,lz1,lelt),vb(lx1,ly1,lz1,lelt)
>
>        common /blasiusr/ u(lx1,ly1,lz1,lelv),v(lx1,ly1,lz1,lelv)
>        common /blasiusg/ bin(lx1,ly1,lz1,lelv)
>        common /scrns/    dum(lx1*ly1*lz1*lelv)
>
>        common /xtream/ psi(lx1*ly1*lz1*lelt)
>       $              , rhs(lx1*ly1*lz1*lelt)
>       $              , h1 (lx1*ly1*lz1*lelt)
>       $              , h2 (lx1*ly1*lz1*lelt)
>
>        parameter (lt=lx1*ly1*lz1*lelt)
>        common /scrns/ vort(lt,3),w1(lt),w2(lt)
>
>        integer bin
>        real normu(50),normv(50)
>
>        real xmax,xmin,dx
>        save xmax,xmin,dx
>
>        n = nx1*ny1*nz1*nelv
>        ifheat=.false.
>        call comp_vort3(vort , w1, w2, vx, vy, vz)
>        call copy (t,vort,n)   ! Vorticity --> T
>        ifto = .true.          ! Dump vorticity as T
> c . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
> c     Compute streamfunction from vorticity
>        call col3 (rhs,t,bm1,n) ! B*omega
>        call rone (h1,n)
>        call rzero(h2,n)
>
>        ifield = 1
>        tol    = param(22)
>        imsh   = 1
>        call hmholtz('psi ',psi,rhs,h1,h2,v1mask,vmult,imsh,
>       $        tol,200,1)
>        call copy (t,psi,n)    ! Psi --> T (for output)
> c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
>
>        nfldt = 1 + npscal
>
>        if (istep.eq.0) call outpost2(vx,vy,vz,pr,t,nfldt,'   ')
>
>        do i=1,n
>           dum(i) = 1.-vx(i,1,1,1)
>        enddo
>        tot_deficit = glsc2(dum,bm1,n)
>        xmin        = glmin(xm1,n)
>        xmax        = glmax(xm1,n)
>        delta_star  = tot_deficit/(xmax-xmin)
>        tmin        = glmin(t,n)
>        tmax        = glmax(t,n)
>        vortmin      = glmin(vort,n)
>        vortmax      = glmax(vort,n)
>        if (nid.eq.0) write(6,1) istep,time,delta_star,vortmin,vortmax
>        if (nid.eq.0) write(6,1) istep,tmin,tmax
>      1 format(i8,1p4e13.5,'  blasius: delta*')
>
>        return
>        end
> c-----------------------------------------------------------------------
>
>
> ________________________________________
> From: Nek5000-users [nek5000-users-bounces at lists.mcs.anl.gov] on behalf of nek5000-users at lists.mcs.anl.gov [nek5000-users at lists.mcs.anl.gov]
> Sent: Tuesday, June 26, 2018 1:22 PM
> To: nek5000-users at lists.mcs.anl.gov
> Subject: Re: [Nek5000-users] Stream function
>
> Hi,
> To correctly compute the stream function, the rhs of the Poisson
> equation needs to be the (negative) vorticity. Therefore, the line
>
>      call col2(rhs,bm1,n)
>
> is wrong, and should be something like
>
>      call col3(rhs, vorticity, bm1, n)
>
> where vorticity should be the computed vorticity using comp_vort.
>
> I guess your calculation of delta* only works for parallel boundary layers.
>
> Philipp
>
>
>
> On 2018-06-26 18:35, nek5000-users at lists.mcs.anl.gov wrote:
>> Hi Phillip,
>>
>> I am using the “Blasius” example test outputting the streamfunction as a
>> scalar.
>>
>> I included my code below. I am not sure what I am doing wrong.
>>
>> In userchk, I added “compute streamfunction from vorticity” from the
>> psi_omega example, but it does not compute the psi properly… (max_psi =
>> min_psi = 0 in every step)
>>
>> c-----------------------------------------------------------------------
>>
>>         subroutine userchk
>>
>>         include 'SIZE'
>>
>>         include 'TOTAL'
>>
>>         common /myblas/ ub(lx1,ly1,lz1,lelt),vb(lx1,ly1,lz1,lelt)
>>
>>         common /blasiusr/ u(lx1,ly1,lz1,lelv),v(lx1,ly1,lz1,lelv)
>>
>>         common /blasiusg/ bin(lx1,ly1,lz1,lelv)
>>
>>         common /scrns/    dum(lx1*ly1*lz1*lelv)
>>
>>         common /xtream/ psi(lx1*ly1*lz1*lelt)
>>
>>        $              , rhs(lx1*ly1*lz1*lelt)
>>
>>        $              , h1 (lx1*ly1*lz1*lelt)
>>
>>        $              , h2 (lx1*ly1*lz1*lelt)
>>
>>         integer bin
>>
>>         real normu(50),normv(50)
>>
>>         real xmax,xmin,dx
>>
>>         save xmax,xmin,dx
>>
>>         n = nx1*ny1*nz1*nelv
>>
>> c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
>>
>> c     Compute streamfunction from vorticity
>>
>>         call col2(rhs,bm1,n)
>>
>>         call rone (h1 ,n)
>>
>>         call rzero(h2 ,n)
>>
>>         tol = param(22)
>>
>>         imsh   = 1
>>
>>         call hmholtz('psi ',psi,rhs,h1,h2,v1mask,vmult,imsh,tol,200,1)
>>
>> c. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
>>
>>         if (istep.eq.0) call outpost(vx,vy,vz,pr,psi,'   ')
>>
>> c     Compute delta*
>>
>>         do i=1,n
>>
>>            dum(i) = 1.-vx(i,1,1,1)
>>
>>         enddo
>>
>>         tot_deficit = glsc2(dum,bm1,n)
>>
>>         xmin        = glmin(xm1,n)
>>
>>         xmax        = glmax(xm1,n)
>>
>>         delta_star  = tot_deficit/(xmax-xmin)
>>
>>         psimin      = glmin(psi,n)
>>
>>         psimax      = glmax(psi,n)
>>
>>         if (nid.eq.0) write(6,1) istep,time,delta_star,psimin,psimax
>>
>>       1 format(i8,1p4e13.5,'  blasius: delta*')
>>
>>         return
>>
>>         end
>>
>>
>>
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>>
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