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-   -   about Nusselt number: local or average? (http://www.cfd-online.com/Forums/fluent/109603-about-nusselt-number-local-average.html)

lbmagis November 21, 2012 13:05

about Nusselt number: local or average?
 
hi every one,
wanna ask u how to find nusselt average and also nusselt local and how to plot them using fluent 6.3 quickly please
thank you so much

ramp November 22, 2012 09:21

For local Nusselt Number
Plot -> XY Plot -> Wall Fluxes... -> Surface Nusselt Number... Select the surface where you want to obtain the local Nusselt number...

You can save the data file or see directly in FLUENT window...

For Average Nusselt Number:

Report -> Surface Integrals -> Report Type -> Facet Average -> Field Variable (Wall Fluxes) --> Surface Nusselt Number....

Again select the surface where you want to obtain the average Nusselt number...

lbmagis November 22, 2012 17:47

Quote:

Originally Posted by ramp (Post 393648)
For local Nusselt Number
Plot -> XY Plot -> Wall Fluxes... -> Surface Nusselt Number... Select the surface where you want to obtain the local Nusselt number...

You can save the data file or see directly in FLUENT window...

For Average Nusselt Number:

Report -> Surface Integrals -> Report Type -> Facet Average -> Field Variable (Wall Fluxes) --> Surface Nusselt Number....

Again select the surface where you want to obtain the average Nusselt number...

thank you so much ramp

lbmagis November 22, 2012 18:56

Quote:

Originally Posted by lbmagis (Post 393719)
thank you so much ramp

for the local nusselt it gave me a graph not a value!how to plot it plz : x direction or y direction?curves or ...?
for the average the average nusselt i got is bigger than nusselt average found in litterature : i am simulating laminar natural convection through an enclosure with partially active wall!!!where's the problem plz tell me ,or give me some steps to simulate this problem from prepossesing to postprossesing
thnk u so much

ramp November 23, 2012 09:22

Quote:

Originally Posted by lbmagis (Post 393727)
for the local nusselt it gave me a graph not a value!how to plot it plz : x direction or y direction?curves or ...?
for the average the average nusselt i got is bigger than nusselt average found in litterature : i am simulating laminar natural convection through an enclosure with partially active wall!!!where's the problem plz tell me ,or give me some steps to simulate this problem from prepossesing to postprossesing
thnk u so much


Rather than plotting the local Nusselt number, you can chose to write in a file and see the values you are interested in.

Average Nusselt number is simply the integration of local values over the selected surface.

Please check the boundary conditions are suitably defined on all the surface...

lbmagis November 23, 2012 14:56

Quote:

Originally Posted by ramp (Post 393821)
Rather than plotting the local Nusselt number, you can chose to write in a file and see the values you are interested in.

Average Nusselt number is simply the integration of local values over the selected surface.

Please check the boundary conditions are suitably defined on all the surface...

OK ramp thank u so much
i have Ra=10^3 ~ 10^6 results,in order to compare them in one graph to see the differences how to do that plz ,iam new in cfd plz help me

lbmagis November 23, 2012 16:57

Quote:

Originally Posted by lbmagis (Post 393886)
OK ramp thank u so much
i have Ra=10^3 ~ 10^6 results,in order to compare them in one graph to see the differences how to do that plz ,iam new in cfd plz help me

Hi again dear ramp,
i have a question in simulation of natural convection through square cavity i obtained Nu average value is 1.289206 for Rayleigh number 10^3!!!in the litterature the Nu average value is 1.118
why?where is the mitakes may be i did???plz if u have a short and brief tutorial could u give me step by step plz from gambit 2.0 to solving on fluent 6.3,i am working for this problem for 2 weeks but i cant got it ,,,i am so tired
thank u ramp for all

ramp November 27, 2012 08:55

Quote:

Originally Posted by lbmagis (Post 393886)
OK ramp thank u so much
i have Ra=10^3 ~ 10^6 results,in order to compare them in one graph to see the differences how to do that plz ,iam new in cfd plz help me


Save the local Nusselt number data for all values of Ra in separate files... Open these files in MS Excel and then combine all the data in one file to plot them on a single graph...

ramp November 27, 2012 08:57

Quote:

Originally Posted by lbmagis (Post 393907)
Hi again dear ramp,
i have a question in simulation of natural convection through square cavity i obtained Nu average value is 1.289206 for Rayleigh number 10^3!!!in the litterature the Nu average value is 1.118
why?where is the mitakes may be i did???plz if u have a short and brief tutorial could u give me step by step plz from gambit 2.0 to solving on fluent 6.3,i am working for this problem for 2 weeks but i cant got it ,,,i am so tired
thank u ramp for all


Are you using the similar numerics (mesh size and numerical schemes, etc.) to that used in the literature? You may try refining the mesh and see the results...

lbmagis November 27, 2012 11:14

i am using 120x120
 
Quote:

Originally Posted by ramp (Post 394389)
Are you using the similar numerics (mesh size and numerical schemes, etc.) to that used in the literature? You may try refining the mesh and see the results...

Hi Ramp, hope ur doing well
i tried : 31x31
41x41
52x52
60x60
80x80
90x90
100x100
110x110
120x120
130x130
161x161
but my results were not good
please Ramp could u help me out?i am really lost
could u teach me the tutorial ste[ by step?or tell me the mistakes i did,here are the steps i ve done:
Gambit2.2:
create surface(1x1 m^2)/mesh: create boundray layer /mesh edges bi-exponent 0.6 and number count 120 for all /mesh surface/define boundary wall/and continum fluid/export .msh and save
fluent 6.3 :
read case/chek/size/scale/display grid
define: solver-enrgy-viscous/materials/operating conditions
Ra=1e+04/boundary conditions
solve:control solution-initialize-residuals-iterate

for compute the Nu average number at y/2 i did:
report/integral surface/facet average/wall flux/surface nusselt number/select heated wall/compute
but my result is not good ,i tried many times
plz tell me how to do all that(post-processing) as : at y/2:
Nu local and average;velocities;temperature...
thank u so much

lbmagis November 27, 2012 11:23

Quote:

Originally Posted by lbmagis (Post 394440)
Hi Ramp, hope ur doing well
i tried : 31x31
41x41
52x52
60x60
80x80
90x90
100x100
110x110
120x120
130x130
161x161
but my results were not good
please Ramp could u help me out?i am really lost
could u teach me the tutorial ste[ by step?or tell me the mistakes i did,here are the steps i ve done:
Gambit2.2:
create surface(1x1 m^2)/mesh: create boundray layer /mesh edges bi-exponent 0.6 and number count 120 for all /mesh surface/define boundary wall/and continum fluid/export .msh and save
fluent 6.3 :
read case/chek/size/scale/display grid
define: solver-enrgy-viscous/materials/operating conditions
Ra=1e+04/boundary conditions
solve:control solution-initialize-residuals-iterate

for compute the Nu average number at y/2 i did:
report/integral surface/facet average/wall flux/surface nusselt number/select heated wall/compute
but my result is not good ,i tried many times
plz tell me how to do all that(post-processing) as : at y/2:
Nu local and average;velocities;temperature...
thank u so much

hi again,
sorry Ramp : at x/2 not y/2
thnks


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