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February 3, 2006, 05:06 
Convergent Divergent Nozzle

#1 
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I am using Fluent 6.1 for my flow analysis. I am having following problems regarding compressible flow.
1)I am using pressure inlet & pressure outlet conditions for ConDi nozzle. I initialized the flow with pressure inlet of 10 bar and velo of 25 m/s as I know the mass flow rate and defined outlet press as 1 bar. The problems are that even after 8000 iterations, the outlet press is 1.45 bar (should be 1.1 bar as per 1D calculations) and mass flow rate shown in Report>flux is 15 kg/s (should be 0.1 kg/s). 2) I am trying to interpolate the above results in the pump using the above nozzle. After reading ip file of nozzle, the contours are not shown in the nozzle area but at the other location. (I used the same nozzle geometry and meshed with same interval count and mesh type in both cases). 3) If I run the jet pump without interpolation, then the flow goes to supersonic conditions without showing pressure drop and velo increase in the nozzle. Please help me. 

February 3, 2006, 11:49 
Re: Convergent Divergent Nozzle

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Fluent has no 'floating' outlet boundary condition. You must estimate the outlet flow static pressure to avoid overexpanded or underexpanded flow at he exit. Best it is to do it by Q1D analysis. Sometimes it is necessary to add additional extension of the nozzle at the outflow boundary to get in 2D or 3D case constant static pressure. Otherwise you may get oscilations, probably like you have.


February 5, 2006, 03:12 
Re: Convergent Divergent Nozzle

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Thank you very much VM. I have already given the outlet flow ststic pressure predicted by 1D analysis. But I haven't given the extension of nozzle at outlet. I will try it.


February 5, 2006, 06:55 
Re: Convergent Divergent Nozzle

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look also at this (tutorial exactly with your case):
http://instruct1.cit.cornell.edu/courses/fluent/ 

February 7, 2006, 04:03 
Re: Convergent Divergent Nozzle

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Thanks. The tutorial is excellent. It is the exact case I want.


October 15, 2009, 00:54 

#6 
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dhanvantri
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Thanks, really its a great tutorial which helped me a lot


September 24, 2011, 05:42 
operating pressure

#7 
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JOSHUA SANTHOSH
Join Date: Sep 2011
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In a converging nozzle what is the operating pressure?I gave it as 1 bar......but after 5 iterations error occurs because of temp increase and what should be the turbulent intensity ratio at inlet and pressure farfield???please help me out


January 4, 2012, 13:16 

#8 
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Angel Briceno
Join Date: Jan 2012
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Hi.
Well I'm new user od this forums, well I´m a studen of Mechanical enginnering from Universidad de carabobo Venezuela, I'm doing a research about convergent divergent nozzle, it's a numerical analysis using ansys cfx. Well I have two priblems: 1) I need to find a dimensions/measures of convergent divergent nozzles used in rockets or military jets. do you know where i find it.? 2) If any of you has worked with dinamical mesh, this for the aproximate of shock waves. Thanks 

January 6, 2012, 02:05 

#9  
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cfdkid
Join Date: Mar 2009
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Hello,
May you find this helpful. All the best, but you would be required to extract data from the files available in the following link about CD nozzle. It is a classic validation study. http://www.grc.nasa.gov/WWW/wind/valid/cdv/cdv.html regards, kid Quote:


January 6, 2012, 11:19 

#10 
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Angel Briceno
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Thanks, I'm really grateful with this information; but I just talking about a nozzle slightly larger likes used in spatial rockets or military jets, if anyone of you have information about where I could find this measures/dimensions of CD nozzle would be helpful, likewise Kid thanks for the help for the information.


January 10, 2012, 16:01 

#11 
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anush
Join Date: Jan 2012
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hi, everybody i am new to the gambit and fluent software, and i needed help solving a converging nozzle problem,i am not getting the convergence in iterations, its actually showing lot of divergence during iteration process,
and it ends with warning like reverse flow at outlet and turbulent flow at outlet. i have selected viscous flow to be spalart allamaras and the courant number as 5. i have used solver as density based and fluid as Air(propertyideal gas). As the iteration progresses the reverse flow and turbulent flow error is shown, after 8090 iterations it shows divergence and accordingly it reduces the courant number from .5 to 5e5 for each iterations and it ends with floatation error. below is image of my model the white region is wall, the pink region is pressure far field, and grey(ish) region is pressure inlet. i need to find the flow characteristics of compressible flow in nozzle. plz plz reply asap... million thanks 

April 5, 2012, 11:43 
Streamlines

#12 
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Angel Briceno
Join Date: Jan 2012
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Hey guys,
Yes, Me again, well I have a new question. when I work in the CFD post and I try to work with the streamlines only I can work whit velocity as variable, and when I try to chance to others variables (like Mach number pressure density) these don't appear in the list of the variables opcions, then did you know how to have o chance to the variables after named with the streamlines?. thanks a lot 

June 25, 2016, 02:06 
Solutions don't converge.

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I am researching on CD nozzles using the geometry and model setup provided in an online tutorial.
https://confluence.cornell.edu/displ...ow+in+a+Nozzle I want to see the flow behaviour as I vary the nozzle pressure ratio. However, when I increase the outlet pressure (>25000 pa), the solutions stop converging. What can be the possible reason for that? 

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