# convergent_divergent nozzle simulation in CFX-11

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 March 20, 2009, 06:21 convergent_divergent nozzle simulation in CFX-11 #1 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 Sponsored Links hi, 1) In CFX-11,Two regims of flows how should analysis actually,take convergent and divergent nozzle (in convergent is subsonic and divergent is supersonic) 1)subsonic 2)supersonic in two region in single model (that means convergent and divergent nozzle in a single geometry in that in that i will give boundary condition inlet of convergent pressure 15 bar steam, throat of pressure 8 bar outlet of 1 bar pressure) i know inlet velocity of steam 856 m/s this is saturation steam. How will analysis in CFX-11,as a hypercritical point of correct results came,but i should verified in CFX-11 SOFTWARE analysis,please let me know. once again thankyou for replay. Actually i done same process,but solution not converging Geometry:combined of convergent and divergent nozzle. Converging and diverging nozzle flow problem My doubt,this model i was created in UNIGRAPHICS modeling software,meshing ICEM CFD, when ever i am giving analysis:at that time some problem is there step2:Boundary condition Fluid :Steam mass flow rate:0.5 kg/s at inlet of convergent nozzle:subsonic condition a)pressure=10 bar;Temperature:356 m/s at outlet of Divergent nozzle :a)supersonic condition . You told this type of settings and simulations given by tutorial 8 from ANSYS CFX release 11.0. in this different : inlet is supersonic condition outlet also supersonic condition but my point of view inlet is subsonic and outlet is supersonic condition __________________ sivaramakrihnaiah

 September 24, 2009, 09:43 B.C at the nozzle for simulation CFX 11.0 #2 New Member   Sudharshani Join Date: Jun 2009 Location: Melbourne,Australia Posts: 16 Rep Power: 10 hai could u pls let know how did u set up the B.C at different conditions(from subsonic.sonic.supersonic and after that catching the expansion and oblique shock waves after exiting the divergent section of the nozzle. as we know the at the exit of the divergent section of the nozzle the pressure condition will be atmospheric so, to capture anything happening in this section do i need to used another B.C as i assume at this stage alltogerther there will be pressure inlet, pressure outlet and something.......at the jet plume region.. could u explain...i am bit confused. thanking sudharshani

 September 25, 2009, 00:52 nozzle #3 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 Hi sudharshani, i was taken in UDF in that i wrote some program . i should send file,tell me your mail ID. Regards Sivaramakrishnaiah from india. __________________ sivaramakrihnaiah

 September 25, 2009, 03:31 mail ID #4 New Member   Sudharshani Join Date: Jun 2009 Location: Melbourne,Australia Posts: 16 Rep Power: 10

 October 1, 2009, 07:03 C-D Nozzle #5 New Member   Jwala Join Date: May 2009 Posts: 10 Rep Power: 10 Hi, Same analysis was done using star cd using afterburner (component of military engine) and c-d nozzle In your case you can define subsonic inlet condition , stagnation temperature and Stagnation pressure at inlet and static pressure at exit of nozzle ie. at the end of divergent duct so that you can see the stable oblique shocks in the divergent section.In unsteady case you can have unstable shocks in convergent section too. with Regards.

 October 9, 2009, 00:47 supersonic CD nozzle #6 New Member   Sudharshani Join Date: Jun 2009 Location: Melbourne,Australia Posts: 16 Rep Power: 10 hai..jwala R Thanks for that.....but CFX-Pre 11.0 i couldn't see Stagnation pressure as a icon under inlet condition. it had only two options : Static Pressure and Total pressure (stable) anyhow....if i set static pressure as 7atm-8atm and left outlet as.. "Opening" BC then how do u generate supersonic flow...... by reducing the outlet pressure to 1atm(which should match the ambient pressure).....would i be able to get smooth(ideally) uniform supersonic flow at exit of my nozzle....? could u help.....pls thanks...so much sudharshani

 October 9, 2009, 00:58 NPR Vs cross section area of supersonic nozzle #7 New Member   Sudharshani Join Date: Jun 2009 Location: Melbourne,Australia Posts: 16 Rep Power: 10 hai..... i would like to know NPR (for supersonic nozzle is somewhere between 7:1 or 8:1) depends on the nozzle geometry( area ratio: exit/throat and inlet/throat)? sudharshani

 October 9, 2009, 01:07 Hi #8 New Member   Jwala Join Date: May 2009 Posts: 10 Rep Power: 10 Hi, Total pressure (stable) can be given as inlet boundary condition. And Static pressure as the outlet boundary condition. Generally you need to give the ambient pressure at the outlet . That depends upon at what height the nozzle is working. Is it at sea level static condition or the distance above the sea level If it is at sea level static condition then you need to see the atmospheric condition of the place. It will differ for a place like africa and canada. Regards, Jwala

 October 9, 2009, 10:27 #9 New Member   Sudharshani Join Date: Jun 2009 Location: Melbourne,Australia Posts: 16 Rep Power: 10 Hai... thanks for that...i will try that. in the mean time i would like to see whats happening at the jet plume area of the nozzle exit( to c how the expansion +oblique shocks are being created)....etc how do i set the boundary condition of the exit of the nozzle as it will also be the (kind of the inlet )of the jet plume section..? iam using CFX-mesh11.0....so how would i set up my model contain two sections: (using ANSYS WB i drew two sketches) (1)sketch1(convergent part+divergent part) (2)sketch 2(jet plume region) as the whole section is extruded in Z diection , i cannot select the outlet on my model(as a "opening" B.C) in CFX Mesh for labeling the regions.. .... i hope u understood the question....some help would a very much appreciated. thank u sudharshani

 October 12, 2009, 08:31 Convergent-divergent nozzle #10 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 HI JAWALA AND SUDARSHANI, I am also simulating convergent and divergent nozzle, My problam convergent is subsonic condition and throat sonic,divergent supersonic condition. inlet pressure 15bar saturation steam Temperature at 198 C, outlet pressure1.5bar, inlet velocity:32 m/s i am simulating 2D model,i given boundary conditions same above mention,, My doubt is two regions is there(subsonic and supersonic) is not taking in CFX solver,what i will do .how to give boundary conditions as per this solution. My GEOMETRY I AM ATTACHING .IGS FORMAT IN the given link: http://www.4shared.com/file/14031536...76/nozzle.html Thanks. __________________ sivaramakrihnaiah

 October 12, 2009, 22:46 Hi #11 New Member   Jwala Join Date: May 2009 Posts: 10 Rep Power: 10 Hi Sudarsini. Have you extended your nozzle? Outlet should be around 6R to 7R from the actual nozzle exit. R is the Nozzle inlet Radius. Similarly you need to extend it vertically to 4R. Siva you can specify Either Total stagnation pressure or velocity based on 1D caculation for compressible flow. Regards, Jwala

 October 12, 2009, 23:12 converging-diverging nozzle #12 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 Good afternoon , in that CFX,and ICEM files. Actually i done same process,but solution not converging Geometry:combined of convergent and divergent nozzle. Converging and diverging nozzle flow problem My doubt,this model i was created in UNIGRAPHICS modeling software,meshing ICEM CFD, when ever i am giving analysis:at that time some problem is there step2:Boundary condition Fluid :Steam mass flow rate:0.5 kg/s at inlet of convergent nozzle:subsonic condition a)pressure=10 bar;Temperature:356 m/s at outlet of Divergent nozzle :a)supersonic condition . from ANSYS CFX release 11.0. in this different : inlet is supersonic condition outlet also supersonic condition but my point of view inlet is subsonic and outlet is supersonic condition __________________ sivaramakrihnaiah

 October 12, 2009, 23:33 #13 New Member   Jwala Join Date: May 2009 Posts: 10 Rep Power: 10 Hi, Assuming the BC'S implied is correct and according to your requirement,Check for Y+ and timestep. What is the error or problemy you faced during simulation? Regards, Jwala

 October 12, 2009, 23:45 converging-diverging nozzle #14 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 Hi jawala, In cfx-11,i given boundary conditions:inlet:total pressure and total temperature with subsonic condition,i want to give out let supersonic,but it showing only subsonic. whats problam. please give me your MSN messanger or google talk ID,i should contact. __________________ sivaramakrihnaiah

 October 12, 2009, 23:51 #15 New Member   Jwala Join Date: May 2009 Posts: 10 Rep Power: 10 Hi. You are getting subsonic condition at outlet.Assuming your solution is converged Actually I am not able to open the link sent by you. What is the outlet static pressure specified and what is ratio of Eit area/Throat area .are you geeting flow choked at throat or sonic condition. Meanwhile i will try to open the link. Regards, Jwala.

 October 12, 2009, 23:58 converging-diverging nozzle #16 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 exit area/inlet area=0.5947, outlet static pressure=1.5bar,inlet total pressure=15 bar, total temperature=198 CALTERNATIVE_GEOMETRICAL_MODEL.jpg __________________ sivaramakrihnaiah

 October 13, 2009, 00:02 converging-diverging nozzle #17 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 INLET DIAMETER:50.8mm, outlet diameter:27.7mm throt diamter:17.7 mm inlet pressure=15 abr,outlet pressure:1.5bar,inlet velocity=32m/s,inlet temperature:198 C __________________ sivaramakrihnaiah

 October 13, 2009, 01:51 Transient analysis #18 Member   mistry Join Date: Apr 2009 Location: India Posts: 69 Rep Power: 10 friends i am also doing analysis of CD nozzle and to have transient flow analysis: for steady state i have: wokng fluid: ideal air inlet pressure:1 bar outlet pressure=0.98,096.,90,.94...... i want to visulise effect of critical pressure ratio tat is at 0.56 but unfortunately i am unable to catch shock... secondly i want to do transient analysis for hthat inlet is same but outlet pressure i assume = p*sinwt. where t i want to vary from 0 to 20 sec. but haw to put this effect.... pleaase do guide me

October 13, 2009, 19:31
Inlet outlet BC, characteristic length
#19
New Member

Sudharshani
Join Date: Jun 2009
Location: Melbourne,Australia
Posts: 16
Rep Power: 10
hai....guys....
yes...i extended the nozzle additional area as a opening BC to cature the jet plume region.
my questions are
(1) how do u know ur Inlet velocity?..... did u get these figures like mass flow rate from any experimental data....?(to my undestanding if a nozzle is operating at 60,000ft then the speed of sound(0.8596m/s) temp(-62C/216K) and ambient pressure(0.043atm) will also be different...isn't it?...i used these
figures ,but didn't give mass flow rate.....only static pressure value for inlet....do u think its correct?

(2) i saw the dimentions u have given,but by my nozzle shape is different.....its cross section is rectangular and is not axsymmetic.....here with i will add for u to see how it looks....(the bigger squre and the curved section is for the jet plume region).....is ur NPR is 15:1?

(3)Which turbulence model are u planing /or have used.....? when calculating k-e model to calculate k,e what is the characteristic length did u use?
is it the cross section of the nozzle or the lengh of the total nozzle?

(4) how did u set outlet BC as supersonic.....iam using CFX 11.0 version (not sure about the 12.0 ver)....it will not allow me ?
i set Ideal real Gas(not air at 25C) assuming it will aloow me to set5 supersonic at outlet..but didn't)

Quote:
 Originally Posted by sivarama1 exit area/inlet area=0.5947, outlet static pressure=1.5bar,inlet total pressure=15 bar, total temperature=198 CAttachment 1245
Attached Images
 Gcleat2.jpg (91.8 KB, 54 views)

Last edited by Sudharshani; October 13, 2009 at 19:50.

 February 18, 2013, 04:05 #20 New Member   Sami Join Date: Sep 2012 Posts: 15 Rep Power: 6 Plz tell me the terms, static pressure, total pressure, static temperature and total temperature with respect to convergent divergent nozzle I m so worried plzz help me I will be thankful

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