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-   -   Compared MRFSimpleFoam and Fluent in a centrifugal pump! (http://www.cfd-online.com/Forums/openfoam-solving/70980-compared-mrfsimplefoam-fluent-centrifugal-pump.html)

renyun0511 December 11, 2009 03:52

Compared MRFSimpleFoam and Fluent in a centrifugal pump!
 
Hi all,
Recently,I am calculating the hydraulic performance and internal field of a centrifugal pump by using OpenFoam-1.5-dev and Fluent.now,I want to recommend my steps.firstly,I generated the mesh in Gambit,save as ***.msh for Fluent and MRFSimpleFoam,and the numerical method i dopted both in Fluent and MRFSimpleFoam are: standard k-epsilon model, simple algorithm and first order upwind.
Additionally,after setting the initial conditions and boundary conditions and the MRF in OF,I modified the discrete format and the under-relaxation factors as followed:
divSchemes
{
default none;
div(phi,U) Gauss upwind;
div(phi,k) Gauss upwind;
div(phi,epsilon) Gauss upwind;
div((nuEff*dev(grad(U).T()))) Gauss linear;
}


fvsolution:
SIMPLE
{
nNonOrthogonalCorrectors 0;
pRefCell 0;
pRefValue 0;
}
relaxationFactors
{
p 0.5;
U 0.5;
k 0.25;
epsilon 0.25;
}
Compared the result in Fluent and MRFSimpleFoam:
the residual,total pressure,absolute velocity in Fluent:
http://www.cfd-online.com/Forums/mem..._residuals.jpg
http://www.cfd-online.com/Forums/mem...nt_p_total.jpg
http://www.cfd-online.com/Forums/mem...v_absolute.jpg

the residual,pressure and velocity in MRFSimpleFoam:
http://www.cfd-online.com/Forums/mem...3-residual.jpg
http://www.cfd-online.com/Forums/mem...cture105-p.jpg
http://www.cfd-online.com/Forums/mem...cture101-u.jpg
http://www.cfd-online.com/Forums/mem...2-vector-u.jpg
http://www.cfd-online.com/Forums/mem...r-velocity.jpg
the hesad and torque:
fluent: head=28.6m, the torque=161.52
OF: head=26.1m,the torque are as followed:

norm of(blade) : (3.35282e-09 3.39945e-09 0.000766278)


pressure torque(blade) : (0 0 0)[Nm]; power: 0[W]


Evaluation of GGI weighting factors:


Largest slave weighting factor correction : 0.000544509 average: 0.000108346


Largest master weighting factor correction: 0.00247013 average: 2.03543e-05


viscous torque (blade) : (0 0 0)[Nm];power 0[W]


norm of(wallqgb) : (-2.0884e-09 -7.9866e-10 -0.0519531)


pressure torque(wallqgb) : (0 0 0)[Nm]; power: 0[W]


viscous torque (wallqgb) : (0 0 0)[Nm];power 0[W]


norm of(wallhgb) : (-1.26442e-09 -2.60051e-09 0.0712859)


pressure torque(wallhgb) : (0 0 0)[Nm]; power: 0[W]

viscous torque (wallhgb) : (0 0 0)[Nm];power 0[W]
at last, my problems are:
1.strangely,when I calculated the impeller without the volute,and the head of impeller is only 20m,why it went up after adding the volute?
2.the p in OF is static pressure,dynamic or total pressure? While which is total pressure in Fluent.
3.Is the residual in OF above convergenced?and how to determine whether the result is convergenced?
4. or is there any things will cause the differents?whether is wrong or right in my setup?
Regards,
Yours jennifer

bastil December 12, 2009 16:57

1.strangely,when I calculated the impeller without the volute,and the head of impeller is only 20m,why it went up after adding the volute?
I did not really unbderstand this.
2.the p in OF is static pressure,dynamic or total pressure? While which is total pressure in Fluent.
p is static pressure. That can not be compared to total pressur ein FLUENT. vmag comparison looks very nice :-)
3.Is the residual in OF above convergenced?and how to determine whether the result is convergenced?
I think it is. To judge convergence this is as difficulat as in any ther CFD code. Maybe try looking at physical values.
4. or is there any things will cause the differents?whether is wrong or right in my setup?
Setup looks good. This is fine I do not think there are large differences between the two codes.

Regards,

renyun0511 December 12, 2009 22:58

hi bastil,
thank you for your reply.
1.a pump is composed of an impeller and an volute.generally speaking,due to the hydraulic lose,the impeller head is often higher than the pump head.and now,the impeller head(20m) is lower than the pump head(26.1m).i don't know why?

4. the torque,which is used for computing the hydraulic efficiency,is difference from each other.from the torque i claculate in OF is too lower than that in Fluent,so the hydraulic efficiency derived from OF is more than 100%,which is virtually impossible in pump industry.

i guess maybe the problem of momentum equation,perhaps,there is absence of something i don't know.there is none of the solvers include coriolis force and centifugal force in my original thinking,but after going into the source case,i saw the description of the forces,and now,i have no ideas.

regards
your jennifer


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