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March 11, 2008, 09:08 
Flow past a sphere

#1 
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Hi all,
I am trying to simulate on a 3D model, a flow past a sphere which is located inside a cylinder, gap width between the sphere face and the cylinder 0.3mm (ball radius 15mm, cylinder radius 15.3mm). I got 750 PSI (it's true, is really high pressure!) pressure difference between the inlet and outlet. My goal is to predict the flow rate and the force action on the ball. As I am not interested to catch the turbulences shear stress and so on, then my mesh isn't too fine, no needs to use EWT. As you see the flow restriction is too small and the pressure is high, which yields huge flow velocities values on the shorter gap area. My point is which viscous model fits better? KE Standard? Realizable? The solver might be Simple or Couple could be used as well? Thanks. 

November 24, 2009, 13:37 
energy eqation in flow past a sphere

#2 
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Muhammed Asmail
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Dear Sir
how are you? i have problem is flow past a sphere,3dimension,unsteady state if the energy equation is applied in flow past a sphere,how the mean value of heat tranfer calculated on surface of the sphere at each time by using FLUENT?,please can you give me the options of FLUENT in order to calculate mean value of heat tranfer calculated on the surface of sphere at each time . i am waiting your reply quickly please,please help me many thanks to you 

November 27, 2009, 15:44 

#3 
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karine
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Hi
go to solve>monitors> and u will find it u will choose to monitor the heattransfer over the sphere surface 

November 27, 2009, 16:37 

#4  
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Muhammed Asmail
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Quote:
thank you very very much for your help,please Sir ,i will go to solve>monitors and aftetr that what i will select (force,surface,volume,..or what),please give me the details step by step ,please my problem is waiting your help, for remember my problem is unsteady state,3dimension,energy equatino,sphere mant thanks to you 

November 27, 2009, 16:50 

#5 
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karine
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Ok
solve>monitors>surface choose 1 surface monitor. Enable plot, print and write in monitor 1: click on define: name: put any name ex:heat transfer coeficient report type: i dont know all report types...Look to Fluent manuel. Me i would put sum, but then u must divide ure data by the surface of ure sphere Report of: choose the variable u want to average Now Fluent will store in a file (because u enabeled write) the sum of the heat transfer coeficient over the sphere surface. U open the file with excel and divide by the sphere surface and u will got the average in function of time Hope that i could be useful sorry for my bad english if i was not clear, rewrite for me and i will try to talk in more details 

November 27, 2009, 16:51 

#6 
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karine
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i forget something: in surfaces, u must select the sphere surface
Regards 

November 27, 2009, 17:10 

#7  
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Muhammed Asmail
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Quote:
dear in field report time ,what i will select (integral,flow rate,sum,...or what) i want to caculate mean value of heat transfer coefficient on the surface of the sphere at each time for example h at 10sec and h at 20sec,,etc no at each node in x axis field what i will select (iteration,time step,flow time) i hope that it is found example for this problem many thanks to you 

November 27, 2009, 17:19 

#8 
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karine
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select integral, but u will get the integral of the heat coefficient over the sphere surface ok? (in function of time)
so u must divide it by the sphere surface to get the the mean value For the rest of ure quetsion, tell me before how much iteration by time step are u performing and i can respond u then. If u understand french, it will be easier to me. Regards 

November 27, 2009, 17:32 

#9 
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Muhammed Asmail
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dear my english is best from my french
i understand on your english your english is very good and no problem your text"so u must divide it by the sphere surface to get the the mean value" how can i divide? my sphere is divided before that in Gambit program my iteration in tim step is 30 as maximum value many thanks to you 

November 27, 2009, 17:40 

#10 
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karine
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of u are interested in a whole profile, u must divide it on excel or matlab...
if u choose area weighted average instead of integral, i think Fluent will divide it for u...but i am not sure....look to the fluent user's guide. 30 iteration per time step is very lot.... Anyway, in the surface monitors panel, choose WHEN TIMESTEP instead of WHEN ITERATION In XAXIS, choose flowtime or timestep.... Fluent will plot for u your variable, and write it in a file too If u still have a problem, contact me (no need to thank me every time ) Good luck and regards comrade 

November 27, 2009, 17:52 

#11  
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Muhammed Asmail
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by the way and at any time can check me what i will select area weighted average instead of integral ??? because fluent user's guide is not availble in my program. my name is Muhammed iraq regards Last edited by Muhammed_iraq; November 29, 2009 at 04:11. 

November 27, 2009, 18:20 

#12  
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Muhammed Asmail
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by the way and at any time can check me what i will select area weighted average instead of integral ??? because fluent user's guide is not availble in my program. my name is Muhammed iraq regards Last edited by Muhammed_iraq; November 29, 2009 at 04:11. 

November 27, 2009, 18:41 

#13 
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karine
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i looked in Fluent user's guide
yes, choose are weighted averag and u will get what u want u can recontact me in case u still have a problem... 

November 27, 2009, 19:11 

#14 
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karine
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hi
u are using a steady or unsteady solver ? 

November 29, 2009, 05:36 

#15 
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Muhammed Asmail
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i am using unsteady state
can you give me relation between Reynold and Nusselt? ,my Re=100,000 in order to check my solution. i have checked cd with experimental work and the accuracy was very good can give me example in actual work about flow past a sphere? regards 

December 3, 2009, 14:00 

#16 
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Matías Rodríguez C.
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HI Muhammed. I'm trying to solve a similar problem. I need to know the global heat transfer coefficient of a sphere (in fact, there are two shperes...one into another, separated with a air gap). The physical problema that i'm trying to solve is the drying of walnuts.
But i'm starting with de simulation of the heat trasnfer. Can we maybe get email contact?. I have convergence problems with my model....how about you?. Which solver and boundary conditions are you using?. Hopingo to get an answer. Best regards Matias 

December 14, 2009, 10:08 

#17 
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Muhammed Asmail
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Dear Karine
i am using unsteady state can you give me relation between Reynold and Nusselt? ,my Re=100,000 in order to check my solution. i have checked cd with experimental work and the accuracy was very good how can i calculate the Strouhal Number(St)by using Fluent? can give me example in actual work about flow past a sphere? i am waiting your replr quickly regards 

December 14, 2009, 10:10 

#18  
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Muhammed Asmail
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Quote:
please explain to me your problem step by step and send it to my email(muham76@yahoo.com) best regards 

December 14, 2009, 17:06 

#19 
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karine
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Hi
For the realtion between Re and Nu, i dont know it, but it is sure that u can find a lot of correlations in bibilography... For the Strouhal number, it is not easy... U must monitor data in a point that is behind ure sphere, then give this data to Matlab and do a fast fourrier transform to get the frequency of ure eddies....Once u have this frequency, u can calculate the Stouhal number...I dont know if this number is affected by temperature in ure case... Regards 

December 15, 2009, 09:54 

#20  
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Muhammed Asmail
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Quote:
thank you very much can give me example to caculate Strouhal number and send it to my email(muham76@yahoo.com)? best regards 

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