[Nek5000-users] Variable density flows

Sat Oct 12 14:04:25 CDT 2013

If you are to use outflow BCs' at the channel exit plane it should be located sufficiently far from the inlet (i.e. the channel length long enough) to allow the flow and scalars to be fully developed d phi /dx =0 
Insulation is usually used at solid walls where there is no gradient in the wall normal direction (no heat or mass flow across the boundary) so it works for temperature and scalars.

try to at least check on mass conservation in an integral sense..

Ammar

On Oct 12, 2013, at 1:29 PM, nek5000-users at lists.mcs.anl.gov wrote:

> Hello
> 
> What type of BC are available for temperature/passive scalar at the outlet of a channel flow ? Can one use the outflow bc 'O' for these scalars ?
> 
> For scalars, when we specify insulated bc 'I' does this set convective+diffusive flux to be zero ?
> 
> Thanks
> praveen
> 
> 
> On Sat, Oct 12, 2013 at 10:58 PM, Praveen Chandrashekar <nek5000 at praveen.e4ward.com> wrote:
> Hi
> My problem is flow in a 2d channel. The initial condition is zero velocity in the channel and there is an inlet flow. I have a passive scalar which is flowing in through inlet. Initial temperature is zero everywhere. I am having trouble getting initial iterations to converge. I am trying stress formulation and passive scalars for first time and I do not see what is going wrong.
> 
> 
>              Solving for heat
>  Solving for fluid F F T
>   Temperature/Passive scalar solution
>    1.0000000000000001E-009  p22            1           2
>  New CG1-tolerance (RINIT*epsm) =    8.4585499354425527E-033   2.               5514287912844953E-033
>   1     1 Helmholtz TEMP    F:   8.4585E-20   1.0000E-09   2.8571E-04   0.0000E+00
>           1    Hmholtz TEMP:      0   8.4585E-20   8.4585E-20   1.0000E-09
>    1.0000000000000001E-009  p22            1           2
>  New CG1-tolerance (RINIT*epsm) =    5.8174583141330990E-032   1.               7860001538991468E-032
>   1     1 Helmholtz PS 1    F:   5.8175E-19   1.0000E-09   2.0000E-03   0.0000E+00
>           1    Hmholtz PS 1:      0   5.8175E-19   5.8175E-19   1.0000E-09
>           1   0.0000E+00  6.0799E-03 Heat done
>  New CG1(stress)-tolerance (RINIT*epsm) =    6.9206392325228944E-014   4.       2096427334076814E-033
>   0  1.0000E-09  6.9206E-14  1.0000E-09 tol,matmod
>            1 tx3:      1   0.3584E+00   0.1000E-08   0.3584E+00
>            1 tx3:      2   0.2546E+00   0.1000E-08   0.3584E+00
>            1 tx3:      3   0.1905E+00   0.1000E-08   0.3584E+00
> .
> .
> .
>            1 tx3:    198   0.1080E-02   0.1000E-08   0.3584E+00
>            1 tx3:    199   0.1067E-02   0.1000E-08   0.3584E+00
>            1 tx3:    200   0.1033E-02   0.1000E-08   0.3584E+00
>      1   201 Unconverged Helmholtz3/Fluid: rbnorm = 0.103306E-02 0.100000E-08
>     1 1.00000E-07 2.34297E-01 2.34297E-01 1.00000E+00       1 Divergence
>  New CG1(stress)-tolerance (RINIT*epsm) =    1.5438583947746548E-016   4.       2096427334076814E-033
>   0  1.0000E-09  1.5439E-16  1.0000E-09 tol,matmod
>            1 tx3:      1   0.8855E-02   0.1000E-08   0.8855E-02
>            1 tx3:      2   0.5463E-02   0.1000E-08   0.8855E-02
>            1 tx3:      3   0.5217E-02   0.1000E-08   0.8855E-02
> 
> Thanks a lot
> praveen
> 
> 
> On Sat, Oct 12, 2013 at 10:04 PM, <nek5000-users at lists.mcs.anl.gov> wrote:
> 
> Hi Praveen,
> 
> That looks right... As always, it's best to run a test
> to verify first.
> 
> Paul
> 
> 
> ----- Original Message -----
> From: nek5000-users at lists.mcs.anl.gov
> To: nek5000-users at lists.mcs.anl.gov
> Sent: Saturday, October 12, 2013 11:17:06 AM
> Subject: Re: [Nek5000-users] Variable density flows
> 
> 
> 
> Thanks to Paul and Ammar. I will try the variable density approach.
> 
> 
> I am first trying a case in which viscosity depends on temperature and a passive scalar. My uservp looks like this. Can I use "temp" and "PS" to get temperature and passive scalar as below ?
> 
> 
> 
> subroutine uservp (ix,iy,iz,ieg)
> include 'SIZE'
> include 'TOTAL'
> include 'NEKUSE'
> common /mygeom/ xmin,xmax
> common /myparam/ r_k,Rey_no,Pr_no,Sc_no,visc_rat
> 
> 
> if(ifield.eq.1)then ! momentum equation
> utrans= 1.0
> udiff = exp(PS(1)*log(visc_rat) - temp)/Rey_no
> else if(ifield.eq.2)then ! temperature eqn
> utrans= 1.0
> udiff = PS(1)*(r_k - 1.0) + 1.0
> udiff = udiff/(Rey_no*Pr_no)
> else if(ifield.eq.3)then ! passive scalar
> utrans= 1.0
> udiff = 1.0/(Rey_no*Sc_no)
> else
> print*,'Only 3 fields'
> call exitt()
> endif
> 
> 
> return
> end
> 
> 
> Thanks
> praveen
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