studies Maryse Page Hydro-Québec, Research Institute Håkan Nilsson Chalmers University of Technology Omar Bounous Chalmers University of Technology

Transcription

1 OpenFOAM Turbomachinery Working Group: ERCOFTAC conical diffuser case-studies studies Maryse Page Hydro-Québec, Research Institute Olivier Petit Chalmers University of Technology Håkan Nilsson Chalmers University of Technology Omar Bounous Chalmers University of Technology Milano, July 2008

2 Outline of the presentation Maryse Page, Håkan Nilsson Description of the ERCOFTAC conical diffuser case-study. Maryse Page and Håkan Nilsson Studies of different geometries, grid types, boundary conditions, linear solvers etc. Omar Bounous Studies of multiple reference frames solutions. Olivier Petit Conclusions Maryse Page and Håkan Nilsson 2

3 Swirling flow in a conical diffuser Maryse Page Ref: P.D. Clausen, S.G.Koh and D.H.Wood, Measurements of a Swirling Turbulent Boundary Layer Developing in a Conical Diffuser, Experimental Thermal and Fluid Science 1993, 6:

4 Swirling flow in a conical diffuser Maryse Page Swirling flow created by a rotating cylinder including a honeycomb screen at its inlet. Swirl at the inlet is close to solid-body rotation. Inlet swirl is sufficient to prevent boundary layer separation along the diffuser wall but just insufficient to cause recirculation in the core flow. Axial pressure gradient and curvature of the streamlines have been found to be the dominant perturbations imposed to the swirling boundary layer as it exits the cylindrical part and enters the conical diffuser. Swirl is responsible for severe radial gradients near the wall for most of the turbulence quantities. 4

5 Experimental techniques Maryse Page Measurements were taken in traverses normal to the wall. Mean velocities: hot-wire anemometer, single wire probe estimated errors: 2% Reynolds stresses: X-wire probe estimated errors: 10% Estimated wall stress using log law of the wall Static pressure: wall taps 5

6 Traverses locations Maryse Page Inlet

7 Streamwise mean velocities Maryse Page Figures taken from Clausen, Koh and Wood, Measurements of a Swirling Turbulent Boundary Layer Developing in a Conical Diffuser, Exp. Th. and Fluid Sci. 1993, 6:

8 Reynolds stresses Maryse Page Figures taken from Clausen, Koh and Wood, Measurements of a Swirling Turbulent Boundary Layer Developing in a Conical Diffuser, Exp. Th. and Fluid Sci. 1993, 6:

9 ERCOFTAC Workshop Maryse Page Testcase 3 from ERCOFTAC Workshop on Data Bases and Testing of Calculation Methods for Turbulent Flows, Karlsruhe, 1995 Testcase 60 from ERCOFTAC Classic database 9

10 How to get the cases and the descriptions Håkan Nilsson _/_ERCOFTAC_conical_diffuser 10

11 How to use the svn How to do a full check-out of all the ERCOFTAC files: svn checkout \ svnroot/openfoam-extend/trunk/breeder/osig/ TurboMachinery/ercoftacConicalDiffuser How to update: svn update How to contribute: svn commit Please discuss with us before you commit. Håkan Nilsson 11

12 Current cases in the Wiki and the svn Håkan Nilsson Case0 Case1 Case2 Case0: Base case Case1: Extended base case Case1.1: Radial mesh Case1.2: MFRSimpleFoam Case1.3: 2D wedge mesh Case2: Case1 with a dump Case2.1: Inlet velocity profile Case2.2: Radial mesh All cases except Case1.2 use simplefoam k-ε with wall functions, average y + : div(phi,u) Gauss linearupwind Gauss; div(phi,k) Gauss upwind; div(phi,epsilon) Gauss upwind; 12

13 Basic procedure of running the cases Håkan Nilsson All cases are parametrized using m4: m4 P blockmeshdict.m4 > blockmeshdict Set inlet boundary condition using: addswirlandrotation (utility), or profile1dfixedvalue (boundary condition) Run using simplefoam or MRFSimpleFoam (default set-up is provided). Post-process using foamlog, sample, and gnuplot scripts. Visualize using a browser. Generate figures for your manuscript using the provided xfig files. 13

14 Case0: Base case Håkan Nilsson Case0 is set up according to the instructions for the original ERCOFTAC workshop. The inlet of the computational domain is located at the first measurement section, and the measurements are used to set the profiles for the velocity and the turbulent quantities (µ T /µ=14.5 to compute dissipation). Using b.c. profile1dfixedvalue. A Neumann boundary condition is used for all other boundary conditions, except for the outlet pressure which is set to zero, and no-slip at walls. The outlet is located at the end of the diffuser. 14

15 Case0: Base case Cross-sections for mesh control (there are m4 parameters for axial locations and mesh density) Håkan Nilsson Cross-section mesh topology and m4 parameters A B C rrelac * rrela * ra m4 parameters diffuserlength rrela * ra ra Inlet, D = 2*rIn z openingangle Outlet, D depends on rin, diffuserlength and openingangle tnumberofcells rnumberofcells 15

16 Case1: Extended base case Håkan Nilsson Extensions are added to reduce the influence of the inlet and outlet boundary conditions. The inlet of the computational domain is located at the beginning of the honeycomb, where a plug flow with a solid body rotation is applied, and the turbulence is specified using a turbulent length scale of m and a turbulent intensity of 10% (µ t /µ=27.3). addswirlandrotation sets solid body rotation at inlet, rotating walls and interior nodes. Neumann boundary conditions are used for all other boundary conditions, except for the outlet pressure which is set to zero, and no-slip at walls. 16

17 Case1: Extended base case Cross-sections for mesh control (there are m4 parameters for axial locations and mesh density) A B C D E F Håkan Nilsson Cross-section mesh topology and m4 parameters Rotating wall 0.5m m4 parameters diffuserlength extensionlength rrelac * rrela * ra rrela * ra Inlet, D = 2*rIn z openingangle Outlet, D depends on rin, diffuserlength and openingangle tnumberofcells ra rnumberofcells 17

18 Case1.1: Case1 with a radial mesh Cross-sections for mesh control (there are m4 parameters for axial locations and mesh density) A B C D E F Håkan Nilsson Cross-section mesh topology and m4 parameters 0.5m m4 parameters diffuserlength extensionlength ra Inlet, D = 2*rIn z openingangle Outlet, D depends on rin, diffuserlength and openingangle rnumberofcells tnumberofcells 18

19 Case1.2: Case1 with MRFSimpleFoam Cross-sections for mesh control (there are m4 parameters for axial locations and mesh density) A B C D E F Håkan Nilsson Cross-section mesh topology and m4 parameters Rotating part (MRF) rrelac * rrela * ra 0.5m m4 parameters diffuserlength extensionlength rrela * ra ra Inlet, D = 2*rIn z openingangle Outlet, D depends on rin, diffuserlength and openingangle tnumberofcells rnumberofcells 19

20 Case1.3: Case1 with a 2D wedge mesh Cross-sections for mesh control (there are m4 parameters for axial locations and mesh density) A B C D E F Håkan Nilsson Cross-section mesh topology and m4 parameters m4 parameters 0.5m diffuserlength extensionlength Inlet, D = 2*rIn x openingangle Outlet, D depends on rin, diffuserlength and openingangle Z Y rnumberofcells 20

21 Case2: Case1 with a dump Håkan Nilsson A dump and a contraction are added to further reduce the influence of the outlet boundary condition. The contraction gives a well-defined flow direction at the outlet. Same boundary conditions as Case1 except for Case2.1, where an inlet velocity profile is specified using b.c. profile1dfixedvalue A Matlab script for generation of the inlet velocity profile is supplied. 21

22 Case2: Case1 with a dump Håkan Nilsson Cross-sections for mesh control (there are m4 parameters for axial locations and mesh density) A B C D E F G H 0.5 m diffuserlength dumplength outletpipelength m4 parameters Inlet, D = 2*rIn Z openingangle Outlet, D depends on rin, diffuserlength and openingangle Diameter of the Dump 22

23 Case2: Case1 with a dump Cross-section mesh topology and m4 parameters Håkan Nilsson rrelac * rrela * ra rrelec * rrele * re rrela * ra rrele * re ra rdump re tnumberofcells rnumberofcells1st tnumberofcells rnumberofcells1st rnumberofcells2nd rnumberofcells3rd 23

24 Case2.1: Case2 with an inlet velocity prof. Cross-section mesh topology and m4 parameters Håkan Nilsson rrelac * rrela * ra rrelec * rrele * re rrela * ra rrele * re ra rdump re tnumberofcells rnumberofcells1st tnumberofcells rnumberofcells1st rnumberofcells2nd rnumberofcells3rd 24

25 Case2.2: Case2 with a radial mesh Håkan Nilsson Cross-section mesh topology and m4 parameters rdump ra re rnumberofcells tnumberofcells rnumberofcells2nd rnumberofcells1st rnumberofcells3rd tnumberofcells 25

26 Studies of solvers, schemes, geometries, grid types, boundary conditions. Case0 Omar Bounous Case1 Case2 Discretization Schemes Linear Solvers Turbulence Models Cross-Section Grid Topologies Linear Solvers Turbulence Models Cross-Section Grid Topologies Inlet Velocity Profile 26

27 Case0 Omar Bounous Div Schemes U k, ε Linear Upwind Upwind Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Boundary Conditions Inlet Outlet U, k, ε p k, ε p Profile from experiments zerogradient zerogradient 0 [kg/ms 2 ] 27

28 Case0 Omar Bounous 28

29 Case1 Discretization Schemes, U, k, ε Upwind Linear Gamma Van Leer Omar Bounous Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k [rad/s] 0.4 [m 2 /s 2 ] ε 3.55 [m 2 /s 3 ] p zerogradient Outlet p, k, ε zerogradient 29

30 Case1 Discretization Schemes, U, k, ε Omar Bounous 30

31 Case1 Discretization Schemes, U, k, ε Omar Bounous 31

32 Case1 Linear Solver for p Smoothers (Gauss-Seidel, DIC, DICGaussSeidel) PCG (Diagonal, GAMG, DIC, FDIC, None) ICCG GAMG Div Schemes Solvers Turbulence Models Boundary Conditions U k, ε U, k, ε k - ε Inlet Outlet GammaV 0.2 Gamma 0.2 PBiCG Axial velocity Tangential velocity Radial velocity Honeycomb rotation k ε p p, k, ε Omar Bounous DILU 11.6 [m/s] Ω * r [m/s] 0 [m/s] [rad/s] 0.4 [m 2 /s 2 ] 3.55 [m 2 /s 3 ] zerogradient zerogradient 32

33 Case1 Linear Solver for p Smoothers Identical U and k results Omar Bounous 33

34 Case1 Linear Solver for p PCG Identical U and k results Problem with pressure Omar Bounous 34

35 Case1 Linear Solver for p Solvers Identical U and k results Convergence very similar Omar Bounous 35

36 Div Schemes Solvers Turbulence Models Boundary Conditions Case1 Linear Solver for p Smoother (DICGaussSeidel) PCG (GAMG) ICCG GAMG U k, ε U, k, ε k - ε Inlet Outlet Linear Upwind Upwind PBiCG Axial velocity Tangential velocity Radial velocity Honeycomb rotation k ε p k, ε p Omar Bounous Default setting in Wiki DILU 11.6 [m/s] Ω * r [m/s] 0 [m/s] [rad/s] [m 2 /s 2 ] [m 2 /s 3 ] zerogradient zerogradient 0 [kg/ms 2 ] 36

37 Case1 Linear Solver for p Omar Bounous Better U and k results Confirmation of the previous study about computational speed and residuals Independence of results from linear solver 37

38 Case1 Turbulence Models k ε k ω SST Omar Bounous Solvers p U, k, ε, ω PCG PBiCG DIC DILU Div Schemes U k, ε Linear Upwind Upwind Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k ε [rad/s] [m 2 /s 2 ] [m 2 /s 3 ] ω 4933 [s -1 ] p zerogradient Outlet k, ε, ω p zerogradient 0 [kg/ms 2 ] 38

39 Case1 Turbulence Models Omar Bounous 39

40 Case1 Turbulence Models Omar Bounous Same computational time 40

41 Case1 Cross-Section Grid Topologies 2D (Wedge) O-Grid Radial Grid Omar Bounous Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Div Schemes U k, ε Linear Upwind Upwind Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Inlet Honeycomb rotation [rad/s] Boundary Conditions k [m 2 /s 2 ] ε [m 2 /s 3 ] p zerogradient Outlet k, ε p zerogradient 0 [kg/ms 2 ] 41

42 Case1 Cross-Section Grid Topologies 2D (Wedge) Omar Bounous 42

43 Case1 Cross-Section Grid Topologies 2D (Wedge) Very different convergence Omar Bounous 43

44 Case1 Cross-Section Grid Topologies 25 cells in the radial direction 80 cells in the circumferential direction (4.5 ) Omar Bounous Three grid topologies with a similar cell density 44

45 Case1 Cross-Section Grid Topologies Convergence in different way Omar Bounous 45

46 Case2 Linear Solver for p PCG (DIC) PCG (GAMG) GAMG Omar Bounous Div Schemes U k, ε Linear Upwind Upwind Solvers U, k, ε PBiCG DILU Turbulence Models k - ε Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Inlet Honeycomb rotation [rad/s] Boundary Conditions k [m 2 /s 2 ] ε [m 2 /s 3 ] p zerogradient Outlet k, ε p zerogradient 0 [kg/ms 2 ] 46

47 Case2 Linear Solver for p Solver for p Omar Bounous 47

48 Case2 Linear Solver for p Solver for p Omar Bounous 48

49 Case2 Turbulence Models k ε k ω SST Omar Bounous Solvers p U, k, ε, ω PCG PBiCG DIC DILU Div Schemes U k, ε Linear Upwind Upwind Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k ε [rad/s] [m 2 /s 2 ] [m 2 /s 3 ] ω 4933 [s -1 ] p zerogradient Outlet k, ε, ω p zerogradient 0 [kg/ms 2 ] 49

50 Case2 Turbulence Models Omar Bounous 50

51 Case2 Turbulence Models Strange spike in the residuals due to parallel problem Omar Bounous 51

52 Case2 Cross-Section Grid Topologies O-Grid Radial Grid Omar Bounous Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Div Schemes U k, ε Linear Upwind Upwind Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Inlet Honeycomb rotation [rad/s] Boundary Conditions k [m 2 /s 2 ] ε [m 2 /s 3 ] p zerogradient Outlet k, ε p zerogradient 0 [kg/ms 2 ] 52

53 Case2 Cross-Section Grid Topologies Omar Bounous 53

54 Case2 Cross-Section Grid Topologies Other strange spike Omar Bounous 54

55 Case2 Inlet Velocity Profile Omar Bounous axial = U b V z U 0 0 U, b x + Cr n [1] Solvers Turbulence Models Div Schemes Boundary Conditions p U, k, ε k - ε U k, ε Inlet Outlet PCG PBiCG Linear Upwind Upwind Tangential velocity Radial velocity Honeycomb rotation k ε p k, ε p DIC DILU Ω * r [m/s] 0 [m/s] [rad/s] [m 2 /s 2 ] [m 2 /s 3 ] zerogradient zerogradient 0 [kg/ms 2 ] [1] W. Gyllenram, H. Nilsson. Very Large Eddy Simulation of Draft Tube Flow. 23rd IAHR Symposium Yokohama,

56 Case2 Inlet Velocity Profile Omar Bounous 56

57 Case2 Inlet Velocity Profile Omar Bounous Same computational time and quite high residuals 57

58 Conclusion Omar Bounous Solution independent from linear solver Solution depends on the order of accuracy of the discretization scheme k ε and k ω SST turbulence models give the same velocity results but different turbulent kinetic energy Difference in the results of different grid topologies is negligible 58

59 Conclusion Omar Bounous 59

60 Case 1.2: Case1 with MRFSimpleFoam Case1.2 Setup of the case Discretization schemes Boundary conditions Different rotation velocities Olivier Petit 60

61 ./makemesh Case1.2 Setup of the case Olivier Petit Mesh generation: m4 -P constant/polymesh/blockmeshdict.m4 > constant/polymesh/blockmeshdict blockmesh.. ercoftacconicaldiffusermrf Selection of cells that should rotate cellsetdict is used cellset.. ercoftacconicaldiffusermrf Selection of faces facesetdict_rotorfaces is used cp system/facesetdict_rotorfaces system/facesetdict faceset.. ercoftacconicaldiffusermrf Remove boundary faces from set facesetdict_noboundaryfaces is used cp system/facesetdict_noboundaryfaces system/facesetdict faceset.. ercoftacconicaldiffusermrf convert the faces into face zone setstozones.. ercoftacconicaldiffusermrf -noflipmap 61

62 Case1.2 Setup of the case Olivier Petit constant/mrfzone: 1 ( ) AB { } AB: Name of the zone (between planes A and B) rotswirlwall: Patch rotating with the zone patches (rotswirlwall); origin origin [ ] (0 0 0); axis axis [ ] (0 0 1); omega omega [ ] ; 62

63 Case1.2 Case1: comparison Same setup as Case1 Olivier Petit Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Div Schemes U k, ε Linear Upwind Upwind Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k ε [rad/s] [m 2 /s 2 ] [m 2 /s 3 ] p zerogradient Outlet k, ε p zerogradient 0 [kg/ms 2 ] 63

64 Case1.2 Case1: comparison Olivier Petit 64

65 Case1.2 Case1: comparison Same computational time and same results Olivier Petit 65

66 Case1.2 Discretization schemes, U/k/ε gamma limitedlinear linear linearuppwind vanleer Olivier Petit Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k [rad/s] [m 2 /s 2 ] ε [m 2 /s 3 ] p zerogradient Outlet p, k, ε zerogradient 66

67 Case1.2 Discretization schemes, U/k/ε Olivier Petit 67

68 Case1.2 Discretization schemes, U/k/ε Olivier Petit linearupwind gives the best results and a good residual - This is the default scheme in the svn 68

69 Case1.2 Outlet boundary condition for p zerogradient fixedvalue fixedmeanvalue The rest of the setup is as before Olivier Petit Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k [rad/s] [m 2 /s 2 ] ε [m 2 /s 3 ] p zerogradient Outlet k, ε zerogradient 69

70 Case1.2 Outlet boundary condition for p Olivier Petit 70

71 Case1.2 Outlet boundary condition for p Olivier Petit Same results but small changes in residuals 71

72 Case1.2 Impact of the rotation Olivier Petit In order to study the impact of the rotation: 1 ( ) AB { patches (); } patches is empty in order to set a constant rotation at rotswirlwall using addswirlandrotation origin origin [ ] (0 0 0); axis axis [ ] (0 0 1); omega omega [ ] ; Omega varies 72

73 Case1.2 Impact of the rotation Omega = 0 Omega = 100 Omega = 1000 The rest of the setup is as before Olivier Petit Solvers p U, k, ε PCG PBiCG DIC DILU Turbulence Models k - ε Axial velocity 11.6 [m/s] Tangential velocity Ω * r [m/s] Radial velocity 0 [m/s] Boundary Conditions Inlet Honeycomb rotation k [rad/s] [m 2 /s 2 ] ε [m 2 /s 3 ] p zerogradient Outlet p, k, ε zerogradient 73

74 Case1.2 Impact of the rotation Olivier Petit 74

75 Case1.2 Impact of the rotation Olivier Petit A high angular velocity affects the accuracy of the results, and might even cause divergence 75

76 General conclusions Maryse Page, Håkan Nilsson The case-study covered various objectives of the Turbo Working Group: Pre-processing, post-processing, utilities Tutorials for training Good validation data Best Practice Guidelines Collaboration Easy diffusion There is a need for more case-studies that cover various aspects of CFD in turbomachinery We invite more people to participate 76