[skace]

Hi, Iam simulating water flow (+-9m/s) in nuclear reactor.
Skewness everywhere in water domain is <0,98.
I have 4 cells out of 4,5 milion with higher skewnes which I can't reduce it by any means.
One of them is 0,995. Will this be a problem if that cell is in solid domain?
Is skewnees just a matter of concern in fluid domains?

[oozcan]

Originally Posted by skace

Hi, Iam simulating water flow (+-9m/s) in nuclear reactor.
Skewness everywhere in water domain is <0,98.
I have 4 cells out of 4,5 milion with higher skewnes which I can't reduce it by any means.
One of them is 0,995. Will this be a problem if that cell is in solid domain?
Is skewnees just a matter of concern in fluid domains?

which package do you use as mesher?

Could you share with your meshing.

Are cells having higher skewness in relatively considerable location?

[skace]

Originally Posted by oozcan

which package do you use as mesher?

Could you share with your meshing.

Are cells having higher skewness in relatively considerable location?

http://imgur.com/a/G7o5V in this area, its adjacent to fluid volume. Its not concentrated in one place, the bad elements are 1meter apart.

[oozcan]

Originally Posted by skace

http://imgur.com/a/G7o5V in this area, its adjacent to fluid volume. Its not concentrated in one place, the bad elements are 1meter apart.

first layer thickness is thin. Probably, aspect ratio is too high as cells having first layer thickness and its adjacent coarse meshes are available. Which method do you use ( curvature, prox-curvature), as far as I am concerned, you might as well run it in this way. Then, do finer mesh and run it again, and you could see what effects high skewness cells are going to be

[oozcan]

and, I would like to see mesh you have done by sending me (onrzcan@hotmail.com)

[Kushal Puri]

Originally Posted by skace

Hi, Iam simulating water flow (+-9m/s) in nuclear reactor.
Skewness everywhere in water domain is <0,98.
I have 4 cells out of 4,5 milion with higher skewnes which I can't reduce it by any means.
One of them is 0,995. Will this be a problem if that cell is in solid domain?
Is skewnees just a matter of concern in fluid domains?

That highly skewed cells may not give problem . You can check, if while doing heat transfer analysis, no temperature shoot-up is there in that region than everything is ok with mesh. Also if you dont want to change the mesh you can turn off the secondary gradient of the temperature or use can use the alternate formulation for temperature calculation (all things i m talking from fluent prespective).

Hope this may help

[skace]

Originally Posted by Kushal Puri

That highly skewed cells may not give problem . You can check, if while doing heat transfer analysis, no temperature shoot-up is there in that region than everything is ok with mesh. Also if you dont want to change the mesh you can turn off the secondary gradient of the temperature or use can use the alternate formulation for temperature calculation (all things i m talking from fluent prespective).

Hope this may help

Energy residual is 1E-8 which is fine for me, btu i have massive continuity problem... residual is only 5E-2. What i do worng?

[Kushal Puri]

Originally Posted by skace

Energy residual is 1E-8 which is fine for me, btu i have massive continuity problem... residual is only 5E-2. What i do worng?

Its not always that your continuity residual should be too less.It depends upon the physics may be some reverse flow may be there. you can monitors some other parameters like mass imbalance and heat flux imbalance if that coming ok, then no need to worry about the continuity residual.

[skace]

Originally Posted by Kushal Puri

Its not always that your continuity residual should be too less.It depends upon the physics may be some reverse flow may be there. you can monitors some other parameters like mass imbalance and heat flux imbalance if that coming ok, then no need to worry about the continuity residual.

Is this source of continuity problem? http://imgur.com/a/U86Sx
Where i can find heatl flux imbalance?

[Kushal Puri]

Originally Posted by skace

Is this source of continuity problem? http://imgur.com/a/U86Sx
Where i can find heatl flux imbalance?

In fluent you go to report and then fluxes there you find both mass as well as heat transfer.

I am not able to see the report can you paste it directly

[skace]

Originally Posted by Kushal Puri

In fluent you go to report and then fluxes there you find both mass as well as heat transfer.

I am not able to see the report can you paste it directly

Mass Flow Rate (kg/s)
-------------------------------- --------------------
interior-hpsi_2-solid -573.10658
interior-hpsi_2-solid.1 -0
interior-hpsi_3-solid 731.32575
interior-hpsi_3-solid.1 -0
interior-hpsi_5-solid 546.10172
interior-hpsi_5-solid.1 -0
interior-sachta-solid 445571.25
interior-sachta-solid-spodek-objem 0.060006303
interior-sachta-solid.1 -0
interior-sani_2-solid 178759.53
interior-sani_2-solid.1 -0
interior-sani_3-solid 178984.5
interior-sani_3-solid.1 -0
interior-sani_5-solid 149351.71
interior-sani_5-solid.1 -0
interior-spodek-objem 180.2848
interior-vstup-solid -26266.429
interior-vstup-solid.1 -0
interior-vytlak_2-solid 102403.84
interior-vytlak_2-solid.1 -0
interior-vytlak_3-solid 104384.28
interior-vytlak_3-solid.1 -0
interior-vytlak_5-solid 107002.32
interior-vytlak_5-solid.1 -0
---------------- --------------------
Net 0

Total Heat Transfer Rate (w)
-------------------------------- --------------------
---------------- --------------------
Net 0

Radiation Heat Transfer Rate (w)
-------------------------------- --------------------
---------------- --------------------
Net 0

[oozcan]

you could just look for inlet and outlet mass flow rate. (that means mass imbalance), that is valid for continuity equation.

[Kushal Puri]

Originally Posted by skace

Mass Flow Rate (kg/s)
-------------------------------- --------------------
interior-hpsi_2-solid -573.10658
interior-hpsi_2-solid.1 -0
interior-hpsi_3-solid 731.32575
interior-hpsi_3-solid.1 -0
interior-hpsi_5-solid 546.10172
interior-hpsi_5-solid.1 -0
interior-sachta-solid 445571.25
interior-sachta-solid-spodek-objem 0.060006303
interior-sachta-solid.1 -0
interior-sani_2-solid 178759.53
interior-sani_2-solid.1 -0
interior-sani_3-solid 178984.5
interior-sani_3-solid.1 -0
interior-sani_5-solid 149351.71
interior-sani_5-solid.1 -0
interior-spodek-objem 180.2848
interior-vstup-solid -26266.429
interior-vstup-solid.1 -0
interior-vytlak_2-solid 102403.84
interior-vytlak_2-solid.1 -0
interior-vytlak_3-solid 104384.28
interior-vytlak_3-solid.1 -0
interior-vytlak_5-solid 107002.32
interior-vytlak_5-solid.1 -0
---------------- --------------------
Net 0

Total Heat Transfer Rate (w)
-------------------------------- --------------------
---------------- --------------------
Net 0

Radiation Heat Transfer Rate (w)
-------------------------------- --------------------
---------------- --------------------
Net 0

You need to select all the things whatever is available not only the interiors for checking the results

[skace]

Originally Posted by oozcan

you could just look for inlet and outlet mass flow rate. (that means mass imbalance), that is valid for continuity equation.

Thats better
Mass Flow Rate (kg/s)
-------------------------------- --------------------
inlet-1 1422.3698
inlet-4 1411.0393
inlet-6 1419.4875
inlet-hpsi2 -0
inlet-hpsi3 -0
inlet-hpsi5 -0
inlet-sani2 1412.9978
inlet-sani3 1411.938
inlet-sani5 1410.2048
outlet-dno -8488.2092
---------------- --------------------
Net -0.17198306

Inlets at HPSI are at start of transient 0 kg/s, so this is ok... Is the net imbalance ok? What could be the reason of such inbalance?

>
Total Heat Transfer Rate (w)
-------------------------------- --------------------
inlet-1 1.4806849e+09
inlet-4 1.4688201e+09
inlet-6 1.4776143e+09
inlet-hpsi2 -22109.282
inlet-hpsi3 -20397.35
inlet-hpsi5 -26342.82
inlet-sani2 1.4695309e+09
inlet-sani3 1.4697556e+09
inlet-sani5 1.4679514e+09
outlet-dno -8.8342267e+09
---------------- --------------------
Net 61699.701

[oozcan]

as far as I am concerned, mass balance difference is very high (0.172 kg/s ), equals to 619,2 kg/hour

[skace]

Originally Posted by oozcan

as far as I am concerned, mass balance difference is 0.172 kg/s is very high, equals to 619,2 kg/hour

Ok its spilling a little bit So where could be the reason why...

[oozcan]

if you are solving for heat transfer, second order upwind schemes give better convergences, which discrete schemes has you chosen? (momentum,energy and turbulence (if there is )

[skace]

Originally Posted by oozcan

if you are solving for heat transfer, second order upwind schemes give better convergences, which discrete schemes has you chosen? (momentum,energy and turbulence (if there is )

http://imgur.com/a/l8lcO Coupled, everything in second order, even energy... Iam simulating for study of heat in metal walls...

[oozcan]

and materials? could you write in or show screenshots?

[skace]

Originally Posted by oozcan

and materials? could you write in or show screenshots?

Water 265°C 12,25Mpa
Steel 7800 kg/m^3
http://imgur.com/a/OlTny