# Strange Velocity in impeller of MRFSimpleFOAM

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 April 10, 2008, 02:44 Hi every one i am trying to #1 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi every one i am trying to simulate the centrifugal impeller with MRFSimpleFoam. after about 5000 steps there are strange velocity in only one passage,the velcity is much larger(above 1e +6 m/s). here is the image of vector plot

 April 10, 2008, 03:10 and here is the residual http #2 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 and here is the residual

 April 10, 2008, 04:00 Take a look at k and epsilon r #3 Senior Member     Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 12 Take a look at k and epsilon residuals and see which starts to diverge first (U, k or epsilon). Then decrease de order of discretization (take upwind for example) for that particular equation. To be on the safe side use upwind for all of them. Dragos

 April 10, 2008, 04:56 Hi Dragos i will try it today #4 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi Dragos i will try it today and here is the p k and epsilon thanks wayne

 April 10, 2008, 05:04 Well Wayne, It seems that k a #5 Senior Member     Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 12 Well Wayne, It seems that k and epsilon are ok, you have to see which starts to diverge first: pressure equation or momentum? Dragos

 April 10, 2008, 05:40 Hi Dragos it looks like there #6 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi Dragos it looks like there are the same and it quit similar to the iteration procedure in cfx(i will post later,for i am not working on that computer),but there is no such strange velocity. thanks wayne

 April 10, 2008, 05:49 Hmm, to me it looks that press #7 Senior Member     Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 12 Hmm, to me it looks that pressure starts to diverge first. So you can try to converge better the pressure equation.

 April 10, 2008, 06:46 Hi Dragos how to? would you #8 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi Dragos how to? would you mind to tell me more ? wayne

 April 10, 2008, 06:56 Hi Wayne, Is your outflow b #9 Member     Eric Lillberg Join Date: Mar 2009 Location: Stockholm Posts: 80 Rep Power: 9 Hi Wayne, Is your outflow boundary the one in the picture or does it only show a part of the whole model. If it is your outflow boundary, what boundary conditions have chosen for it? Also, post an image of your mesh or the output from the checkMesh utility. Regards //Eric

 April 10, 2008, 07:05 I use this seting for the pres #10 Senior Member     Dragos Join Date: Mar 2009 Posts: 648 Rep Power: 12 I use this seting for the pressure equation (fvSolution): p PCG {
preconditioner GAMG {
tolerance 1e-6; relTol 0.05; smoother DICGaussSeidel; nPreSweeps 0; nPostSweeps 2; nBottomSweeps 2; cacheAgglomeration false; nCellsInCoarsestLevel 10; agglomerator faceAreaPair; mergeLevels 1; }; tolerance 1e-6; relTol 0.05; maxIter 100;
};

 April 10, 2008, 07:25 To Eric: i use the fixedValue #11 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 To Eric: i use the fixedValue in p for my output condition. the calcualtion region is a impeller without the voulte,so you can see them on the first image! Wayne

 April 10, 2008, 07:27 To Dragos thanks! i will #12 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 To Dragos thanks! i will try! Wayne

 April 10, 2008, 08:27 Wayne, Your outflow boundar #13 Member     Eric Lillberg Join Date: Mar 2009 Location: Stockholm Posts: 80 Rep Power: 9 Wayne, Your outflow boundary is way to close to the region where things happen to allow for fixed pressure BC. Use totalPressure BC instead together with appropriate BC's for U pressureInletOutletVelocity, k inletOutlet and epsilon inletOutlet. Regards /eric

 April 10, 2008, 22:50 Hi: i try to run the case in #14 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi: i try to run the case in the parallel again without change anything in fvSolution.i still get a divergence. but the different is i donot get strange velocity like before,and the velocity is also looks quiet strange.it looks like that there is no velocity inlet just angular velocity everywhere including the velocity inlet. here is the residual

 April 10, 2008, 22:51 and is the velocity in 0.5 spa #15 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 and is the velocity in 0.5 spanwise

 April 10, 2008, 22:53 and the velocity in 0.5spanwis #16 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 and the velocity in 0.5spanwise in CFX

 April 11, 2008, 02:12 Hi Eric would you mind to se #18 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi Eric would you mind to send one of your setting(such as makemesh/fvSolution/fcScheme/MRFZones/dynamicMeshDict/Boudary/0 dictionary )or me ? thanks! wayne

 April 11, 2008, 02:41 Sure, Send your e-mail adr #19 Member     Eric Lillberg Join Date: Mar 2009 Location: Stockholm Posts: 80 Rep Power: 9 Sure, Send your e-mail adress to eric.lillberg@afconsult.com /E

 April 11, 2008, 03:01 Hi My email adress is wayne #20 Senior Member   wayne.zhang Join Date: Mar 2009 Location: Shanghai, Shanghai, P.R.China Posts: 307 Rep Power: 10 Hi My email adress is waynezw0618@163.com i have sent a email to you.if it was too large for you to send me.please send the setting files(such as makemesh/fvSolution/fcScheme/MRFZones/dynamicMeshDict/Boudary/0 dictionary or other)to me! thanks! wayne

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