# Nozzle flow

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 November 6, 2007, 13:13 Nozzle flow #1 Gayathri Guest   Posts: n/a Hi all, I am new to CFX. I am trying to model a subsonic-supersonic nozzle. Could u help me on what the flow regime should be? inlet says subsonic. but I am not able to choose any option for the supersonic outlet? is static pressure is sufficient?

 November 7, 2007, 18:40 Re: Nozzle flow #2 Glenn Horrocks Guest   Posts: n/a Hi, There is a discussion in the manual about selection of sub/super sonic inlets and outlets. Have a read of that section as it should help you. Glenn Horrocks

 November 8, 2007, 05:53 Re: Nozzle flow #3 Jim Guest   Posts: n/a I'm sure you've already done this, but make sure you are solving the energy equation. When I've done ConDi nozzles in the past, the most stable BC combination was fixed velocity inlet and supersonic outlet (I think, it was a while ago). Hope this helps.

 November 9, 2007, 08:55 Re: Nozzle flow #4 Wei Chen Guest   Posts: n/a hi Gayathri, I think you should set the boundary condition like this: inlet:total pressure outlet:average static pressure you needn't concern the "supersonic outlet" regards.

 November 9, 2007, 14:50 Re: Nozzle flow #5 gayathri Guest   Posts: n/a Hi Glenn and Jim, thanks.. I did try out the inlet total pressure and the average static pressure..i need to try out the one Glenn mentions. I never could fix a supersonic outlet..I shall try both out. Thanks!

 November 9, 2007, 14:50 Re: Nozzle flow #6 gayathri Guest   Posts: n/a @Jim, I never did try that,, will do thanks!

 November 12, 2007, 02:13 Re: Nozzle flow #7 prabhu Guest   Posts: n/a Depending on the nozzle pressure ratio there could be flow separation and backflow through outlet. So better give "Opening" bc with "static pressure for opening"

 November 19, 2007, 07:05 Re: Nozzle flow #8 Dhananjaya Rao Guest   Posts: n/a 1. If you are solving nozzle problem in CFX. You use the subsonic inlet at inlet condition and assign supersonic outflow condition at outlet (I assume that nozzle is with divergent portion also). 2. You need to use energy equation as it is compressible flow analysis. 3. The most important in this problem is good approximation of the flow field. Otherwise u wont get solution. you should look at the outlet flow conditions as per the isentropic relations and assign those values or nearer to the entire flow field. You will get in less than 200 iterations. All the best

 November 19, 2007, 08:25 Re: Nozzle flow #9 prabhu Guest   Posts: n/a Supersonic outlet bc is apt only if the flow is underexpanded or adapted. What if the flow is overexpanded?

 March 20, 2009, 07:11 #10 Member   sivaramakrishnaiah Join Date: Mar 2009 Location: india,pondicherry Posts: 76 Rep Power: 10 i am also simulating convergent and divergent nozzle, 1) In CFX-11,Two region 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. ,i am sending .rar file,please verify it, 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 . 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 1)i was increased mesh size 2)That flow direction changed 3)Fluidry steam taken 4)Same boundary conditions But does not converging(up to 200 iterations converging),what i am thinking know up to convergent portions was converged.after that it is not converging,) convergent nozzle:solution converging . Divergent nozzle:solution not converging as per velocity plot.and pressure plot. Actually pressure should drop and velocity should increases.but in this condition; 1)convergent to throat :velocity increases and pressure droping 2)Throat to Divergent nozzle:Velocity not increasing and pressure not droping. What is the problem. i am thinking Two solutions(means subsonic and supersonic condition will not give in single solution) that is correct or not,please verify that. Thank you very much. __________________ sivaramakrihnaiah

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