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Help needed with my Converging diverging nozzle

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Old   November 4, 2017, 14:22
Post Help needed with my Converging diverging nozzle
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Mohammed Sorwar
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I am designing a converging diverging nozzle for my 3rd year dissertation any tips on geometry. I have created this geometry do you think its adequate enough i am going to use the asymmetric function in fluent. I have used split face on the geometry to capture the effects on the important areas of interest but ansys fluent is giving me floating point exception error any suggestions would be great to increase effectiveness thanks also when i run the simulation i had reversed back flow thanks in advance.
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Old   November 5, 2017, 20:33
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Alexander
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Why do you think that reversed back flow is not normal for this case?

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Old   November 6, 2017, 07:47
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Quote:
Originally Posted by AlexanderZ View Post
Why do you think that reversed back flow is not normal for this case?

Best regards
Hi Alexander, I appreciate you replying to my post you are correct in regards to the reversed back flow it is expected in this application do you have any suggestions to the floating point exception which i am getting an error for its stop the simulation after 150 or so iterations preventing me from running it again unless the error is fixed. Also is there a way for me to find out the pressure through the sections of the nozzle and is there a way to measure the radius at different sections of the nozzle so i can carry out some hand calculations thanks sorry for so many questions

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Sorwar
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Old   November 6, 2017, 14:05
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Bhanu Mahesh
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Hi Sorwar,
I partially understood your question but let me give you some suggestions regarding the possible errors u might have made.

If ur flow is compressible.
Check
In Materials>Air
Check that density is kept to "ideal gas".
If temperature is high, use Sutherland law to the viscosity of air.
Make sure u r using density based solver.
There are few more suggestions, but let's try with the above changes, and try to rectify the errors to get the approximate solutions.

Best wishes,
Bhanu Mahesh.
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Old   November 7, 2017, 17:43
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Mohammed Sorwar
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Quote:
Originally Posted by bhanumahesh1993 View Post
Hi Sorwar,
I partially understood your question but let me give you some suggestions regarding the possible errors u might have made.

If ur flow is compressible.
Check
In Materials>Air
Check that density is kept to "ideal gas".
If temperature is high, use Sutherland law to the viscosity of air.
Make sure u r using density based solver.
There are few more suggestions, but let's try with the above changes, and try to rectify the errors to get the approximate solutions.

Best wishes,
Bhanu Mahesh.
Hi Bhanu,
Thank you for your recommendation of changing pressure based to Density based solver, I am now getting the error around 360 iterations . However my results are still not what i am expecting running the simulation i got the following results maby they are to do with the assigned parameters of pressures, temperatures and velocity i have assigned ?

I have added pictures of the fluent settings i have used

Inlet Conditions
Gauge total pressure/ Stagnation pressure =1835000pa
Initial Gauge pressure =1200000pa
Total Temperature/ Stagnation temperature =534K
Inlet (x) velocity = 348.8m/s

Outlet conditions
Gauge Pressure = 720000pa
Back flow Total temperature= 408.7K

Regards Sorwar
Thanks for the help
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File Type: jpg 4.jpg (37.5 KB, 13 views)
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Old   November 7, 2017, 20:15
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Alexander
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You may try to use Coupled Scheme (in solution methods) with pseudo transient option.

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Old   November 8, 2017, 17:24
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Bhanu Mahesh
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https://www.youtube.com/watch?v=oY_3_c0rDiw
I hope this video helps. Just have a look
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