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5. CFD Enhancements

5. CFD Enhancements

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5. CFD Enhancements

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  1. 5. CFD Enhancements

  2. CFD Enhancements 5.1 ALE (Arbitrary Lagrangian Eulerian) Formulation • The fluid mesh may now have prescribed movement 5.2 Surface Tension Effects • 2D - Quadrilateral elements 5.3 Radiation in Flotran 5.4 Additional Algebraic Solver (BiCGStab) 5.5 Tabular Boundary Conditions 5.6 Interpolation of results onto a different mesh • Refine the mesh and keep going 5.7 FSSOLV Macro • Steady State Fluid Structure Interaction (FSI) 5.8 AUX3 - Results File Editor Training Manual 001419 15 Aug 2000 5-2

  3. 5.1 ALE Formulation CFD Enhancements

  4. CFD EnhancementsALE Formulation • ALE - Arbitrary Lagrangian Eulerian formulation for CFD analyses • Typical ANSYS Applications • moving walls, solids moving through fluids • ANSYS 5.7 Target • Rigid body FSI for MEMS devices( squeeze film damping, torsional mirrors) • Extract damping/spring forces on moving body for reduced order modeling • Interpretation and manipulation of FLOTRAN results data Training Manual 001419 15 Aug 2000 5-4

  5. CFD Enhancements… ALE Formulation • ALE allows for deforming/moving fluid domains • Nodes are allowed to move in space to accommodate moving bodies • User specifies displacements & velocities time history for moving body and turns ALE on (FLDA,SOLU,ALE,T) • Mesh morphing is based on constrained Laplacian smoothing Training Manual 001419 15 Aug 2000 5-5

  6. CFD Enhancements… ALE Formulation • Example: squeeze film Training Manual 001419 15 Aug 2000 5-6

  7. CFD Enhancements… ALE Formulation • Example: torsional oscillation Training Manual 001419 15 Aug 2000 5-7

  8. CFD Enhancements… ALE Formulation • Example: Comb drive problem - MEMS application Mesh Deformation History Rigid Body Translation Training Manual 001419 15 Aug 2000 5-8

  9. CFD Enhancements… ALE Formulation • Limitations in ANSYS 5.7: • Incompressible flows and adiabatic compressible flows • Cartesian XY and axisymmetric in 2D • Cartesian XYZ in 3D • Small mesh deformations • Applied motion to additional lines enables larger motions • 3D mesh morphing limited to tets or hex/wedge combination • Free surface can be used via ALE-VOF combination capability Training Manual 001419 15 Aug 2000 5-9

  10. CFD Enhancements… ALE Formulation • Constraining the motion of nodes Boundary layer capturing box: all nodes in the box are moved along with the plate surface Motion constrained on lines Pressure Velocity Training Manual 001419 15 Aug 2000 5-10

  11. CFD Enhancements… ALE Formulation Squeeze film problem - circular plate r=0 r=R Pressure=P0 Fixed Wall h0 t=0 Moving wall t=5 t=10 Mesh Deformation History Static Pressure Contours History Training Manual 001419 15 Aug 2000 5-11

  12. CFD Enhancements… ALE Formulation Squeeze film problem (cont'd) • Analytical Result • Pressure force on moving plate = 1.5*p*m*(1/h**3)*dh/dt*R**4 = 42,411 • Assumption is h/R << 1(negligible inertia) • FLOTRAN Results • At t=10: Pressure = 42,828 (h/R->0.01) Training Manual 001419 15 Aug 2000 5-12

  13. 5.2 Surface Tension CFD Enhancements

  14. CFD EnhancementsSurface Tension • CLEAR - VOF Formulation • Computational Lagrangian Eulerian Advection Remap - Volume Of Fluid • Works for mapped or free 2D Quadrilateral Mesh • CSF Model • Continuum Surface Force • Balance of Forces • Body Forces (E.G. Centrifugal Force) • Gravity • Continuum Surface Force • Tendency to Maintain a Surface Wetting Angle is a Characteristic of fluid and wall Training Manual 001419 15 Aug 2000 5-14

  15. CFD Enhancements… Surface Tension • Applications • Ink-Jet printers • Mold Filling • Micro-fluid handling (MEMS devices) • Input • Surface Tension Coefficient • Wetting Angle (defaults to 90 degrees) • Normal to Surface Training Manual 001419 15 Aug 2000 5-15

  16. CFD Enhancements… Surface Tension Fluid in a Spinning Cylinder Low Wetting Angle (5 deg) High Wetting Angle (175) Training Manual 001419 15 Aug 2000 5-16

  17. CFD Enhancements… Surface Tension Oscillating Water Droplet Training Manual 001419 15 Aug 2000 5-17

  18. 5.3 Radiation in FLOTRAN CFD Enhancements

  19. CFD EnhancementsRadiation in FLOTRAN • Generalized radiation analysis with two or more radiating surfaces for FLUID141 and 142 • Supported only for incompressible flow thermal analysis • Features: • Radiation solution using radiosity method • Temperature dependent emissivity • Multiple open/closed enclosures • Radiation analysis does NOT support symmetry BC's Training Manual 001419 15 Aug 2000 5-20

  20. CFD Enhancements… Radiation in FLOTRAN • Features (cont'd): • 3-D radiation analysis • View factor calculation using the Hemicube method • NOT supported for r-theta-z coordinate system • 2D radiation analysis • View factor calculation using ANSYS double integration method • Supports plane and axisymmetric geometry about YR and XR coordinate system • NOT supported for r-theta coordinate system Training Manual 001419 15 Aug 2000 5-21

  21. CFD Enhancements… Radiation in FLOTRAN Procedure: 1. Define radiating surfaces using SF family of commands SF,,RDSF,EMIS,ENCL # • EMIS: Surface emissivity value, between {0,1} or -N (material number N) for temperature dependent emissivity • ENCL: Radiation enclosure number • Positive number for radiation away from the element (for solid elements) • Negative number for radiation into the element (for fluid elements) • All surfaces seeing each other should have the same enclosure number Training Manual 001419 15 Aug 2000 5-22

  22. CFD Enhancements… Radiation in FLOTRAN Procedure (cont'd): 2. Activate thermal analysis option • FLDATA, SOLU, TEMP,1 3. Define FLOTRAN analysis options • Define material properties for solid and fluid elements • Define reference conditions for temperature Training Manual 001419 15 Aug 2000 5-23

  23. CFD Enhancements… Radiation in FLOTRAN Procedure (cont'd): 4. Define radiosity method options • Define Stefan Boltzsman constant STEF & temperature offset TOFFST • Define radiosity solution options RADOPT • Define Space temperature/Space node for open enclosures (SPCTEMP/ SPCNOD) • View Factor options • Define options for 3D/2D view factor calculation HEMIOPT / V2DOPT • Define view factor calculation option VFOPT • RDSF BC's are only supported for wall type boundaries Training Manual 001419 15 Aug 2000 5-24

  24. CFD Enhancements… Radiation in FLOTRAN Procedure (cont'd): 5. Calculate & query view factors • Calculate view factors VFCALC • View factors are stored in file - jobname.vf • Query calculated view factors VFQUERY • View factors can be calculated either in RADIATION or are automatically calculated/ read during SOLUTION depending on options set using VFOPT Training Manual 001419 15 Aug 2000 5-25

  25. CFD Enhancements… Radiation in FLOTRAN Procedure (cont'd): 6. Postprocessing • Output for radiation heat flow is turned on by default for thermal analysis in FLOTRAN with surface radiation • FLDATA, OUTP, RDFL, 1 • Main output quantity is radiation heat flow, RDFL • PLNSOL, RDFL ! Contours • PRNSOL, RDFL ! Listing • PDEF,,RDFL,,AVG ! Path item • NSOL,,,RDFL ! POST26 Training Manual 001419 15 Aug 2000 5-26

  26. 5.4 Algebraic Solver CFD Enhancements

  27. CFD EnhancementsAlgebraic Solver • PBCGM • Preconditioned Bi-Conjugate Gradient Method • Also known as Bi-CGSTAB • Preconditioning allows fill in the matrix LU decomposition • Applications • General: ~7% faster than PCG for incompressible flow. • Will handle some ill-conditioned problems better • Long aspect ratio pipe flow models • Usage • User specifies Fill, number of search vectors Training Manual 001419 15 Aug 2000 5-28

  28. CFD EnhancementsAlgebraic Solver • GUI implementation Training Manual 001419 15 Aug 2000 5-29

  29. 5.5 Interpolation CFD Enhancements

  30. CFD EnhancementsInterpolation • Think the mesh is too coarse in only one small area? • Recirculation region, shock wave, etc. • Refine the mesh, make it a new jobname, and restart from the previous results! • Specify results file to start from • Specify which results set to start from • Easily done in interactive or batch mode • Note - you should save copies of the original database and results file. Training Manual 001419 15 Aug 2000 5-32

  31. CFD Enhancements… Interpolation Access Refinement Through Mesh Tool Training Manual 001419 15 Aug 2000 5-33

  32. CFD Enhancements… Interpolation 50 global Iterations Result of 5 more global iterations on the new mesh Training Manual 001419 15 Aug 2000 5-34

  33. CFD Enhancements… Interpolation Training Manual 001419 15 Aug 2000 5-35

  34. CFD Enhancements… Interpolation 900 global iterations 20 more G.I. Pressure contours - shock wave now sharper near the body! Training Manual 001419 15 Aug 2000 5-36

  35. 5.6 Tabular Boundary Conditions CFD Enhancements

  36. CFD EnhancementsTabular Boundary Conditions • Tabular boundary conditions are now available for the FLOTRAN DOF • VX,VY,VZ,PRES,TEMP,ENKE,ENDS,SP01….SP06 • Commands to apply tabular BC • D,DL,DA,SF,SFE,SFL,SFA • See CFD Analysis Guide for example • Arbitrary Lagranian Eulerian (ALE) Formulation for Moving Domains • ALE Analysis of a Simplified Torsional Mirror Training Manual 001419 15 Aug 2000 5-38

  37. CFD Enhancements… Tabular Boundary Conditions • Applications: • Drive ALE moving boundary problems. • Time varying flow for transients Training Manual 001419 15 Aug 2000 5-39

  38. CFD Enhancements… Tabular Boundary Conditions • Dialog Boxes for DL, DA, D commands have changed! • Choice could be existing table... • Also may create table Training Manual 001419 15 Aug 2000 5-40

  39. CFD Enhancements… Tabular Boundary Conditions • Name the table and its rows, columns and planes Training Manual 001419 15 Aug 2000 5-41

  40. CFD Enhancements… Tabular Boundary Conditions • Fill it in…. Flow versus Time Training Manual 001419 15 Aug 2000 5-42

  41. CFD Enhancements… Tabular Boundary Conditions Training Manual 001419 15 Aug 2000 5-43

  42. 5.7 FSI Macro FSSOLV CFD Enhancements

  43. CFD EnhancementsFSI Macro FSSOLV • Creates a recursive loop for Fluid Structure Interaction (FSI) problems. • Based on the use of Physics files • They contain element assignment, loads, solver options • Morphing is used to change the mesh in response to the structural solution • User defines region(s) that will move and makes a named component out of it. • Convergence: rate of change between loop passes • Force & moment (INTSRF) - based on fluid physics • Displacement - based on structural physics Training Manual 001419 15 Aug 2000 5-46

  44. CFD Enhancements… FSI Macro FSSOLV • Example: flow over a “cement wall” (but Elasticity reduced by 100 to create larger displacement….) • Morphed region in red boxes • Element aspect ratios should be near 1.0 ! • Nodal locations are updated in the database • FSSOLV macro automatically saves a copy of the original database…. • Create an area component that includes all the regions that must be morphed. • Lines or areas that are shared by regions not to be morphed will remain unchanged. Training Manual 001419 15 Aug 2000 5-47

  45. CFD Enhancements… FSI Macro FSSOLV Training Manual 001419 15 Aug 2000 5-48

  46. CFD Enhancements… FSI Macro FSSOLV • Access “Physics” from PREP7 or SOLU: Training Manual 001419 15 Aug 2000 5-49

  47. CFD Enhancements… FSI Macro FSSOLV Training Manual 001419 15 Aug 2000 5-50

  48. 5.8 AUX3 CFD Enhancements

  49. CFD EnhancementsAUX3 • AUX3 provides a results file editing capability • Works on all ANSYS results files • Enables control of size of result file! • No GUI • Functions • Eliminate sets of results from .rfl file • Combine two results files • take some sets from each file • List Function • Which exist • Which marked for deletion Training Manual 001419 15 Aug 2000 5-52

  50. CFD Enhancements… AUX3 • Commands - No GUI! • FILE,filename,extension,directory • Identifies the file to be operated on • DELETE,SET,nstart,nend • Delete sets by set number • UNDELETE,SET,nstart,nend • Keep these sets • UNDELETE,ALL • Start over picking which ones to delete • COMPRESS • Executes the deletion of sets so indicated Training Manual 001419 15 Aug 2000 5-53