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August 8, 2012, 08:42 
rhoPorousMRFSimpleFoam/compressor simulation blows up

#1 
New Member
Maja Patarcic
Join Date: May 2012
Posts: 2
Rep Power: 0 
Hi all,
I am trying to simulate a compressible flow in centrifugal compressor (for turbocharger) with rhoPorousMRFSimpleFoam (OF 2.1.1 Version). I am modeling the inlet duct, the impeller and the outlet diffusor. I have 3 domains: statorrotorstator. For Interfaces I use cyclicAMI. To save computing time I am using cyclic boundary conditions. The impeller is rotating with 160000 rpm. I started using komega SST Modell with wall function. This simulation runs for ca. 600 Iterations but eventually blows up because time step continuity errors rise. Pressure and omega residuals diverge. Then I checked my y+ with yPlusRAS utility and it reported y+ < 1. When I use no wall functions for k and mut the simulation runs for ca. 5500 Iterations but then same happens. In ParaView I see one cell (on blade) where pressure and omega increase dramatically. I think it is mesh problem. My mesh is generated with ICEM CFD. It is tetra mesh with prism boundary layer. ICEM reports no errors and the quality is good enough for CFX. In OpenFOAM checkMesh reports some non orthogonal and few skew faces, but with checkMesh –allTopology –allGeometrie there are some underdetermined cells additionally reported. Some of these faces/cells are located on blade where error occurs. How do I proceed with these errors? How to avoid these underdetermined cells? Could this be the reason for the simulation blow up? I would really appreciate your help. Thanks in advance ;) Maja checkMesh.log Case 

August 9, 2012, 13:54 

#2 
Member

Hi Maja,
If the checkMesh reports nonOrthogonal and skewed cells, then there is a very good chance that the blowup is because of the mesh. Try changing the nNonOrthogonalCorrectors and also initializing the simulation using potentialFoam. This should definitely help the case. As an example  I was analyzing the flow through a very complex 2 substrate catalytic converter for which I built the mesh in snappy. The mesh looked good and checkMesh showed an error of only 3 skewed cells. But when I ran the case, I never got it to converge to good results if the nNonOrthogonalCorrectors were less than 10 !!!! I know that sounds absurd but it is true. I still am not able to figure out why I had to use so many correctors if according to foam I had no nonOrthogonal cells and only 3 skewed cells. So, try fiddling with those correctors. Most of the time, your potentialFoam solution itself can be a clue to whether your solution will converge or not ( continuity and interpolated U error should be as close to 1 as possible if not below it ) You can use this criterion to fine tune the number of correctors u need. Kalyan 

August 10, 2012, 09:52 

#3 
New Member
Maja Patarcic
Join Date: May 2012
Posts: 2
Rep Power: 0 
Huhu Kalyan,
Thank you for your advice. Can you please tell me how can I initialize my flow with potentialFoam if the flow velocity results from impeller rotational speed? I have Total Pressure, Total Temperature and zeroGradient for velocity on Inlet. I have tested it with flowRateInletVelocity and pressureInletOutletVelocity on outlet. I need ca. 15 nNonOrthogonalCorrectors but same error happens eventually: Code:
Time = 519 smoothSolver: Solving for Ux, Initial residual = 0.00689174020389124, Final residual = 0.0001811298084334255, No Iterations 2 smoothSolver: Solving for Uy, Initial residual = 0.007125217146934263, Final residual = 0.0001859035926144115, No Iterations 2 smoothSolver: Solving for Uz, Initial residual = 0.01007109609581601, Final residual = 0.0002720657574050938, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 0.01189626781015002, Final residual = 0.0004430857512486936, No Iterations 1 GAMG: Solving for p, Initial residual = 0.525246072638058, Final residual = 0.02234065612714114, No Iterations 2 GAMG: Solving for p, Initial residual = 0.1210393076383517, Final residual = 0.004059726915845455, No Iterations 2 GAMG: Solving for p, Initial residual = 0.03711323447992431, Final residual = 0.001207459503253744, No Iterations 2 GAMG: Solving for p, Initial residual = 0.01390244007788457, Final residual = 0.0004040200625956493, No Iterations 2 GAMG: Solving for p, Initial residual = 0.005329744823495349, Final residual = 0.0001524608155663665, No Iterations 2 GAMG: Solving for p, Initial residual = 0.002159844936659785, Final residual = 6.187981539139611e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0009000768414453766, Final residual = 2.614056448078217e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000387175087517713, Final residual = 1.142583341601287e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0001718465581034602, Final residual = 5.160508215150291e06, No Iterations 2 GAMG: Solving for p, Initial residual = 7.794569833811138e05, Final residual = 2.266434677289963e06, No Iterations 2 GAMG: Solving for p, Initial residual = 3.477625348436517e05, Final residual = 1.019722809542639e06, No Iterations 2 GAMG: Solving for p, Initial residual = 1.57441454955239e05, Final residual = 4.360974326864854e07, No Iterations 2 GAMG: Solving for p, Initial residual = 6.92933500221939e06, Final residual = 2.016293952604061e07, No Iterations 2 GAMG: Solving for p, Initial residual = 3.173510949418744e06, Final residual = 8.7284304841048e08, No Iterations 2 GAMG: Solving for p, Initial residual = 1.421339504689786e06, Final residual = 4.250775374814685e08, No Iterations 2 GAMG: Solving for p, Initial residual = 6.693670543287874e07, Final residual = 1.860688605016314e08, No Iterations 2 time step continuity errors : sum local = 0.0006145710207738517, global = 2.659732169674872e05, cumulative = 0.0003956096006971732 rho max/min : 1.785699960099344 0.5971102771881479 smoothSolver: Solving for omega, Initial residual = 0.002288630882997602, Final residual = 4.497457628363702e05, No Iterations 1 smoothSolver: Solving for k, Initial residual = 0.003047717993801081, Final residual = 6.695371931754372e05, No Iterations 1 ExecutionTime = 21.46 s ClockTime = 22 s Time = 520 smoothSolver: Solving for Ux, Initial residual = 0.00685892500157054, Final residual = 0.0001781598558160968, No Iterations 2 smoothSolver: Solving for Uy, Initial residual = 0.007116418862045025, Final residual = 0.0001839081410649369, No Iterations 2 smoothSolver: Solving for Uz, Initial residual = 0.009954523806062012, Final residual = 0.0002701273723458191, No Iterations 2 DILUPBiCG: Solving for h, Initial residual = 0.01185654992594479, Final residual = 0.0004422577762352827, No Iterations 1 GAMG: Solving for p, Initial residual = 0.5217401646589753, Final residual = 0.02240546892794447, No Iterations 2 GAMG: Solving for p, Initial residual = 0.1204252318653997, Final residual = 0.004028617590806268, No Iterations 2 GAMG: Solving for p, Initial residual = 0.03687051608255586, Final residual = 0.001180687618896112, No Iterations 2 GAMG: Solving for p, Initial residual = 0.01358671728843339, Final residual = 0.0003956252492256043, No Iterations 2 GAMG: Solving for p, Initial residual = 0.005212434153393288, Final residual = 0.0001467219739165364, No Iterations 2 GAMG: Solving for p, Initial residual = 0.002095649830267571, Final residual = 5.831582947256874e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0008761050175603406, Final residual = 2.583571916038806e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.000383257128952095, Final residual = 1.131748182531108e05, No Iterations 2 GAMG: Solving for p, Initial residual = 0.0001711316968720861, Final residual = 5.052897435634979e06, No Iterations 2 GAMG: Solving for p, Initial residual = 7.631093755718225e05, Final residual = 2.260425128892119e06, No Iterations 2 GAMG: Solving for p, Initial residual = 3.449474051643401e05, Final residual = 1.012405010496451e06, No Iterations 2 GAMG: Solving for p, Initial residual = 1.549985569778341e05, Final residual = 4.635358865057642e07, No Iterations 2 GAMG: Solving for p, Initial residual = 7.111843979700321e06, Final residual = 2.083560348490843e07, No Iterations 2 GAMG: Solving for p, Initial residual = 3.208706672168953e06, Final residual = 9.71363574529989e08, No Iterations 2 GAMG: Solving for p, Initial residual = 1.492962361641866e06, Final residual = 4.395685059333027e08, No Iterations 2 GAMG: Solving for p, Initial residual = 6.775063608301946e07, Final residual = 2.080044109382489e08, No Iterations 2 time step continuity errors : sum local = 0.0007113392680664244, global = 2.948635003943702e06, cumulative = 0.0003926609656932295 rho max/min : 1.788032591204212 0.5965712276411931 smoothSolver: Solving for omega, Initial residual = nan, Final residual = nan, No Iterations 1000 smoothSolver: Solving for k, Initial residual = nan, Final residual = nan, No Iterations 1000 ExecutionTime = 26.1 s ClockTime = 26 s Time = 521 smoothSolver: Solving for Ux, Initial residual = nan, Final residual = nan, No Iterations 1000 smoothSolver: Solving for Uy, Initial residual = nan, Final residual = nan, No Iterations 1000 smoothSolver: Solving for Uz, Initial residual = nan, Final residual = nan, No Iterations 1000 DILUPBiCG: Solving for h: solution singularity Code:
Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 14639 faces: 149430 internal faces: 139886 cells: 72329 boundary patches: 17 point zones: 0 face zones: 3 cell zones: 3 Overall number of cells of each type: hexahedra: 0 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 72329 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Topological cell zipup check OK. Faceface connectivity OK. <<Writing 93 cells with with two nonboundary faces to set twoInternalFacesCells *Number of regions: 3 The mesh has multiple regions which are not connected by any face. <<Writing region information to "0/cellToRegion" Checking patch topology for multiply connected surfaces ... Patch Faces Points Surface topology Bounding box ROTOR_HUB 543 381 ok (nonclosed singly connected) (0.005940277634 0.02298990972 0.01023706532) (0.01757740074 0.0006413035989 0.03043711472) ROTOR_BLADE 2101 1115 ok (nonclosed singly connected) (0.01002530289 0.02249982629 0.0102374897) (0.01391894245 0.003520271167 0.02794919761) ROTOR_SHROUD 930 524 ok (nonclosed singly connected) (0.01691088676 0.02299648304 0.01732514381) (0.01749520845 0.001966941138 0.03042087057) INLET_DUCT 562 326 ok (nonclosed singly connected) (0.01691089439 0.01562956807 0.03043420009) (0.002200154341 0.0006411794424 0.05291999435) INLET 145 90 ok (nonclosed singly connected) (0.01691079521 0.01562951296 0.05291694634) (0.002200275083 0.0006411794424 0.05291999435) OUTLET 463 268 ok (nonclosed singly connected) (0.008105474472 0.04616911035 0.01021563911) (0.03538647188 0.02966462808 0.01584203791) OUTLET_DUCT 977 563 ok (nonclosed singly connected) (0.008105474472 0.04616911035 0.01021563911) (0.03538647188 0.01484315558 0.01732754156) OUTLET_INTERFACE_SLAVE182 111 ok (nonclosed singly connected) (0.004198823929 0.02300056671 0.01023706436) (0.01757749445 0.01484315558 0.01732754156) OUTLET_INTERFACE_MASTER434 252 ok (nonclosed singly connected) (0.004199062824 0.0229972754 0.01023706532) (0.01757740074 0.01484326831 0.01733062408) INLET_INTERFACE_SLAVE147 90 ok (nonclosed singly connected) (0.01691089439 0.01562918925 0.03043420009) (0.002200161517 0.0006413034201 0.03043730953) INLET_INTERFACE_MASTER386 219 ok (nonclosed singly connected) (0.01691088676 0.0156291945 0.03041778481) (0.002200161362 0.0006413035989 0.03043711472) INLET_PER1 197 120 ok (nonclosed singly connected) (0.01691089439 0.001968802096 0.03043711472) (0.005511092863 0.0006411794424 0.05291999435) INLET_PER2 197 120 ok (nonclosed singly connected) (0.006751238925 0.01562956807 0.03043711472) (0.002200154341 0.005093347119 0.05291999435) OUTLET_PER1 236 138 ok (nonclosed singly connected) (0.008105474472 0.04547789764 0.01021563911) (0.004065802574 0.02262504959 0.01732515335) OUTLET_PER2 236 138 ok (nonclosed singly connected) (0.01749445574 0.02975333815 0.01021563911) (0.03538647188 0.01484315558 0.01732515335) ROTOR_PER1 904 499 ok (nonclosed singly connected) (0.01691088676 0.02264410973 0.01023706532) (0.003978910923 0.0006413035989 0.03043711472) ROTOR_PER2 904 499 ok (nonclosed singly connected) (0.006751214565 0.01706289718 0.01023706532) (0.01757740074 0.005093398461 0.03043711472) Checking geometry... Overall domain bounding box (0.01691089439 0.04616911035 0.01021563911) (0.03538647188 0.0006411794424 0.05291999435) Mesh (nonempty, nonwedge) directions (1 1 1) Mesh (nonempty) directions (1 1 1) Boundary openness (1.008508880210902e16 6.737618413690084e17 1.747059006460879e17) OK. Max cell openness = 2.258267238391119e16 OK. Max aspect ratio = 4.580087858669184 OK. Minumum face area = 2.13575888608433e08. Maximum face area = 3.238582471401818e06. Face area magnitudes OK. Min volume = 2.152195729490874e12. Max volume = 1.713436717452314e09. Total volume = 1.106455360888172e05. Cell volumes OK. Mesh nonorthogonality Max: 65.86404963883847 average: 18.07799753123574 Nonorthogonality check OK. Face pyramids OK. Max skewness = 0.5164240204619981 OK. Coupled point location match (average 2.823201989552231e12) OK. Face tets OK. Min/max edge length = 0.0001148631272861437 0.003225834417998265 OK. All angles in faces OK. All face flatness OK. Cell determinant (wellposedness) : minimum: 0 average: 1.449341833456967 ***Cells with small determinant found, number of cells: 266 <<Writing 266 underdetermined cells to set underdeterminedCells Concave cell check OK. Failed 1 mesh checks. End Code:
Create time Create polyMesh for time = 0 Time = 0 Mesh stats points: 119506 faces: 1285019 internal faces: 1228117 cells: 628284 boundary patches: 17 point zones: 0 face zones: 3 cell zones: 3 Overall number of cells of each type: hexahedra: 0 prisms: 0 wedges: 0 pyramids: 0 tet wedges: 0 tetrahedra: 628284 polyhedra: 0 Checking topology... Boundary definition OK. Cell to face addressing OK. Point usage OK. Upper triangular ordering OK. Face vertices OK. Topological cell zipup check OK. Faceface connectivity OK. <<Writing 231 cells with with two nonboundary faces to set twoInternalFacesCells *Number of regions: 3 The mesh has multiple regions which are not connected by any face. <<Writing region information to "0/cellToRegion" Checking patch topology for multiply connected surfaces ... Patch Faces Points Surface topology Bounding box ROTOR_HUB 3534 2059 ok (nonclosed singly connected) (0.005945404573 0.02299999161 0.01023706532) (0.01757740074 0.0006413035989 0.03043711472) ROTOR_BLADE 15837 8090 ok (nonclosed singly connected) (0.01006028831 0.02249981902 0.0102374897) (0.01391894245 0.003480050475 0.02794864382) ROTOR_SHROUD 6125 3202 ok (nonclosed singly connected) (0.01691088676 0.02299888183 0.01732514381) (0.01749520845 0.001966371457 0.03042126661) INLET_DUCT 2550 1384 ok (nonclosed singly connected) (0.01691089439 0.01562956806 0.03043419193) (0.002200154339 0.0006411794424 0.05291999435) INLET 635 356 ok (nonclosed singly connected) (0.01691079521 0.01562951296 0.05291688432) (0.002200275083 0.0006411794424 0.05291999435) OUTLET 1274 714 ok (nonclosed singly connected) (0.008105474472 0.04616953992 0.01021563911) (0.03538647188 0.02966462808 0.01584203305) OUTLET_DUCT 7277 3809 ok (nonclosed singly connected) (0.008105474472 0.04616953992 0.01021563911) (0.03538647188 0.01484315558 0.01732754528) OUTLET_INTERFACE_SLAVE837 465 ok (nonclosed singly connected) (0.004198823929 0.023002 0.01023706436) (0.01757749445 0.01484315558 0.01732754528) OUTLET_INTERFACE_MASTER2663 1412 ok (nonclosed singly connected) (0.004199062824 0.02299999161 0.01023706532) (0.01757740074 0.01484326831 0.01733062769) INLET_INTERFACE_SLAVE667 372 ok (nonclosed singly connected) (0.01691089439 0.01562918925 0.03043419193) (0.002200161517 0.0006413034201 0.03043731022) INLET_INTERFACE_MASTER531 298 ok (nonclosed singly connected) (0.01691088676 0.0156291945 0.03041780696) (0.002200161362 0.0006413035989 0.03043711472) INLET_PER1 1230 671 ok (nonclosed singly connected) (0.01691089439 0.00196880207 0.03043711472) (0.005511092863 0.0006411794424 0.05291999435) INLET_PER2 1230 671 ok (nonclosed singly connected) (0.006751238924 0.01562956806 0.03043711472) (0.002200154339 0.005093347119 0.05291999435) OUTLET_PER1 667 376 ok (nonclosed singly connected) (0.008105474472 0.04547789764 0.01021563911) (0.004065802574 0.02262504959 0.01732515335) OUTLET_PER2 667 376 ok (nonclosed singly connected) (0.01749445574 0.02975333815 0.01021563911) (0.03538647188 0.01484315558 0.01732515335) ROTOR_PER1 5589 2908 ok (nonclosed singly connected) (0.01691088676 0.02264410973 0.01023706532) (0.003978910923 0.0006413035989 0.03043711472) ROTOR_PER2 5589 2908 ok (nonclosed singly connected) (0.006751214566 0.01706552291 0.01023706532) (0.01757740074 0.005093398461 0.03043711472) Checking geometry... Overall domain bounding box (0.01691089439 0.04616953992 0.01021563911) (0.03538647188 0.0006411794424 0.05291999435) Mesh (nonempty, nonwedge) directions (1 1 1) Mesh (nonempty) directions (1 1 1) Boundary openness (1.333273483219948e16 2.025107292171666e16 1.062012456559783e16) OK. Max cell openness = 2.372167083931545e16 OK. Max aspect ratio = 4.349712291115716 OK. Minumum face area = 2.251662057643688e09. Maximum face area = 6.317981495047761e07. Face area magnitudes OK. Min volume = 9.282675234161758e14. Max volume = 1.647429053664735e10. Total volume = 1.107251948954049e05. Cell volumes OK. Mesh nonorthogonality Max: 50.17858023799637 average: 16.47284712748219 Nonorthogonality check OK. Face pyramids OK. Max skewness = 0.6033462107301415 OK. Coupled point location match (average 2.327840432511681e12) OK. Face tets OK. Min/max edge length = 4.764886039802482e05 0.001414873923756246 OK. All angles in faces OK. All face flatness OK. Cell determinant (wellposedness) : minimum: 0 average: 1.574006420034666 ***Cells with small determinant found, number of cells: 773 <<Writing 773 underdetermined cells to set underdeterminedCells Concave cell check OK. Failed 1 mesh checks. End Thanks Maja 

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