[Nek5000-users] About the iobj in the drag calculation
nek5000-users at lists.mcs.anl.gov
nek5000-users at lists.mcs.anl.gov
Thu May 29 12:00:15 CDT 2014
Hi Xianbi,
You are right in defining the Reynolds Stresses.
However, if you look carefully, this is an example of fully developed
turbulent Channel. Hence the statistics is independant of the x direction
(streamwise). Also, the statistics is taken independant of z direction (no
wall in z). x and z both have periodic BC. Hence before calculating R_uu,
R_vv etc, we just do the spatial planar averaging in the xz plane. Since
for homogeneous flow, that should equal an ensemble average.
You can modify the turbChannel to a non-homogeneous flow, in which case you
can define Reynolds stresses just like you said, and they would spatially
varying.
Thanks,
Tanmoy
On Thu, May 29, 2014 at 5:22 AM, <nek5000-users at lists.mcs.anl.gov> wrote:
> Hi,Paul:
> I'm confused about part of the subroutine userchk in turbChannel.usr
> if(icalld.eq.0) then
> call rzero(uavg,n)
> call rzero(urms,n)
> call rzero(vrms,n)
> call rzero(wrms,n)
> call rzero(uvms,n)
> atime = 0.
> timel = time
> call planar_average_s(yy ,ym1 ,w1,w2)
> icalld = 1
> endif
>
> dtime = time - timel
> atime = atime + dtime
>
> if (atime.ne.0. .and. dtime.ne.0.) then
> beta = dtime/atime
> alpha = 1.-beta
> ifverbose = .false.
>
> call avg1(uavg,vx ,alpha,beta,n,'uavg',ifverbose)
> call avg2(urms,vx ,alpha,beta,n,'urms',ifverbose)
> call avg2(vrms,vy ,alpha,beta,n,'vrms',ifverbose)
> call avg2(wrms,vz ,alpha,beta,n,'wrms',ifverbose)
> call avg3(uvms,vx,vy,alpha,beta,n,'uvmm',ifverbose)
>
>
> dragx_avg = alpha*dragx_avg + beta*0.5*(dragx(1)+dragx(2))
>
> ! averaging over statistical homogeneous directions (r-t)
> call planar_average_s(uavg_pl,uavg,w1,w2)
> call planar_average_s(urms_pl,urms,w1,w2)
> call planar_average_s(vrms_pl,vrms,w1,w2)
> call planar_average_s(wrms_pl,wrms,w1,w2)
> call planar_average_s(uvms_pl,uvms,w1,w2)
>
> ! average over half the channel height
> m = ny1*nely
> do i=1,ny1*nely/2
> uavg_pl(i) = 0.5 * (uavg_pl(i) + uavg_pl(m-i+1))
> urms_pl(i) = 0.5 * (urms_pl(i) + urms_pl(m-i+1))
> vrms_pl(i) = 0.5 * (vrms_pl(i) + vrms_pl(m-i+1))
> wrms_pl(i) = 0.5 * (wrms_pl(i) + wrms_pl(m-i+1))
> enddo
> endif
>
> tw = dragx_avg/A_w + 1.e-50
> u_tau = sqrt(tw/rho)
> Re_tau = u_tau*delta/dnu
>
> diff = (tw-ffx_new)/tw
> if(nid.eq.0) write(6,1) istep,time,e2,ffx_new,diff
> 1 format(i6,1p4e17.9,' err2')
>
> ! write statistics to file
> iostep_avg = param(68)
> if(nid.eq.0 .and. istep.gt.0 .and.
> & mod(istep,iostep_avg).eq.0) then
> write(6,*) 'Dumping statistics ...'
> open(unit=56,file='reystresses.dat')
> write(56,'(A,1pe14.7)') '#time = ', time
> write(56,'(A)')
> & '# y y+ R_uu R_vv R_ww R_uv'
> open(unit=57,file='means.dat')
> write(57,'(A,1pe14.7)') '#time = ', time
> write(57,'(A)')
> & '# y y+ Umean'
>
> m = ny1*nely/2
>
> do i=1,m
> write(56,3) yy(i)+1
> & ,(yy(i)+1)*Re_tau
> & , (urms_pl(i)-(uavg_pl(i))**2)/u_tau**2
> & , vrms_pl(i)/u_tau**2
> & , wrms_pl(i)/u_tau**2
> & , uvms_pl(i)/u_tau**2
> write(57,3) yy(i) + 1.
> & , (yy(i)+1.)*Re_tau
> & , uavg_pl(i)/u_tau
> 3 format(1p15e17.9)
> enddo
>
> close(56)
> close(57)
> endif
>
> return
> end
>
> I look into the code of navier5.f and find that avg1, avg2 returns the
> time average of vx and vx**2 in this example, so if we want to calculate
> the Reynolds stress, the formulation should be :
> R_uu=urms-uavg**2
> also, if normalized,
> R_uu=(urms-uavg**2)/u_tau**2
> so are the other components
> I think this is the right way instead of that in the example
>
>
>
>
>
>
> At 2014-05-29 06:54:10, nek5000-users at lists.mcs.anl.gov
> wrote:
> >
> >Hi Xianbei,
> >
> >You can define more objects by picking your
> >own surface discriminators (which will
> >be dependent on your particular application).
> >
> >If you need more than 4 objects, you can increase maxobj
> >in SIZE.
> >
> >Typically, dragx(0) would be the sum of the drag on all
> >the objects --- this is sometimes useful.
> >
> >If you have (say) a 4-sided channel, you can just define
> >one object instead of 4, and set it to be the collection
> >of all faces for which cbc(f,e,1)='W '.
> >
> >Paul
> >
> >
> >
> >On Thu, 29 May 2014, nek5000-users at lists.mcs.anl.gov wrote:
> >
> >> Hi,all:
> > I read Paul's reply in this mail https://lists.mcs.anl.gov/mailman/htdig/nek5000-users/2014-May/002756.html
>
> > And got to know something about objects. As you say, the object is a collection of faces, here , I have a question about the iboj, how could I know which face it represent with iboj? As in turbChannel.usr,
> > dragx_avg = alpha*dragx_avg + beta*0.5*(dragx(1)+dragx(2))
> > I think it means to do the time-average of the average dragx on planey1 and planey2, as
> > 0.5*(dragx(1)+dragx(2))
> > indicates, while how to calculate the dragx on the planex1, planex2, planez1 and planez2? for the maxobj in this example is only 4 and dragx is defined as
> > dragx(0:maxobj)
> >
> >Thank you
> >Xianbei
> >_______________________________________________
> >Nek5000-users mailing list
> >Nek5000-users at lists.mcs.anl.gov
> >https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
>
> 来自网易手机号码邮箱了解更多 <http://shouji.163.com>
>
> _______________________________________________
> Nek5000-users mailing list
> Nek5000-users at lists.mcs.anl.gov
> https://lists.mcs.anl.gov/mailman/listinfo/nek5000-users
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.mcs.anl.gov/pipermail/nek5000-users/attachments/20140529/0ab1b10e/attachment.html>
More information about the Nek5000-users
mailing list