Learning Forum

[sharmaanand_cfd]

Dear Sir,

I am student of Final year engineering and working on design of rocket nozzle using CFD tool Fluent 2019R3 Academic.

I have attached image herewith which I am trying to achieve through simulation .

I am able to get shock inside the nozzle and also the over expanded and under expanded regions.

But not able to get Design condition results which is shock free supersonic flow.

I am attaching file here.

Please guide me on this.

If you have any sample tutorial on Design condition will be helpful.

[RK]

Hello, nAs Ansys employees, we will not be able to download the file. However other members in the community are welcome to do so. To address your question, can you please give more details on the setup and what issue you are facing? n

[sharmaanand_cfd]

Dear Sir,nnAs you can see in the attached image at design condition NO WAVES are formed CASE F.nBut even after putting design condition pressure ratio I am getting wavy structure.nnIt is a very basic problem of CD Nozzle where we need to reduce back pressure to achieve design points .nnIf possible please mail me solution at following email idnEmail removed: please keep the discussion on here so others can learn. nnThanks and RegardsnAnandnnn

[sharmaanand_cfd]

Dear Sir/Madam,nAwaiting for your reply.nThanks & Regards,nAnandn

[Rob]

We're also waiting for details on the set up as requested. When you read the rules you'd have seen staff are not permitted to open or download files. n

[sharmaanand_cfd]

Dear Sir,nThis is very standard problem of CD Nozzle as I mentioned above.nHere I have tried both steady and transient Density Bases Solver with following parameters.nTURBULENCE MODEL : INVSCID , K-EPSILON, K-OMEGA ALL TRIEDnDensity : AIR (IDEAL GAS)nCD NOZZLE AREA RATIO : 1.25 HENCE CORRESPONDING PRESSURE RATIO FOR DESIGN CONDITION = 0.235 (P_INLET = 7 bar and P_OUTLET = 1.64 bar.) nAll the solver settings are DEFAULT.nActually I am able to capture shock inside the CD Nozzle and could validate it.nI have gone through online tutorials / videos but could not see any simulation with DESIGN CONDITIONnSee attached image to have look at design condition contours.nnPlease let me know if you need more information.nHope to see some positive response.nRegards,nAnandnn

[RK]

Hello Anand, nIf you were able to validate the results, what exactly is your question about design condition? n

[sharmaanand_cfd]

Good Morning,nNot able to validate design condition results as plot is having shock which is not expected.nExpected plot is as above which I am not able to produce.nAs mentioned earlier also this is standard problem of CD Nozzle which have (Over expanded, Design Condition and Under expanded regimes)nHope this clears everything !!nRegardsnAnandn

[Aitor]

Hello Anand,nAs you say, this is the typical converging-diverging nozzle problem. I suppose that the geometry and stagnation enthalpy are fixed, so that you have only one variable: inlet pressure. Euler equations with additional simplifications (steady and isentropic flow, negligible mass forces...) lead to an algebraic system of equations whose solutions are indeed tabulated, so that you have an starting point to validate your results. These tabulated values also give you the operating regime of the nozzle depending on the stagnation inlet pressure. nFor these type of flows, I would recommend you the following:n1) Obtain the mentioned tabulated (or obtained with a nonlinear equation solver) results and get the values of the inlet pressure for the different regimes (subsonic, supersonic with shock waves inside the nozzle, supersonic without shock waves, supersonic with shock waves outside the nozzle, supersonic with expansion and shock waves outside the nozzle).n2) Perform numerical simulations for these cases. Starting with the subsonic case, you can check if numerical results give the expected regime, as well as verify other quantities as throat and outlet velocity.nBe careful with the domain extension and mesh quality if shock waves and/or expansion waves are present. If you have any discrepancy in any of the simulations, you can post here your problem.

[sharmaanand_cfd]

Thanks Aitor!!nI have begun the discussion with same.nI am getting all the regimes but shock free contour plot for Design Condition as shown above.nI also attached the Workbench file in first post itself.nHere I am playing back pressure keeping inlet stagnation pressure constant.nHope to get solution in this forum.nn

[RK]

Anand, nWanted to check with you if the contour plot that you have, is it a converged solution? Also the contour plot you have inserted, is it steady state or transient? Are you also monitoring a value in the computational domain? If so, can you please insert an image of that. n

[sharmaanand_cfd]

Dear RK,nI have tried both steady as well as transient, steady is reaching 1e-2 but transient is very well converging.nI am monitoring Mach Number at Nozzle Exit which is becoming flat.nFew useful links.nnn