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
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3. 5.1 ALE Formulation
CFD Enhancements

4. CFD Enhancements ALE 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
ALE and VOF are both considered in CFD to be alternatives to the free surface problem. At 5.7 however, the ALE formulation is only implemented for displacement driven problems.
Extracting damping and spring forces depends upon learning the phase angle between the applied displacement and the resulting force response.. This comes from comparing plots of the force response and the displacement (applied) as a function of time.
Analytic solutions are typically based on perturbation theory, and thus have geometrical limitations.
Training Manual
15 Aug 2000
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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
The formulation of the advection terms in the Navier-Stokes equations must be modified to account for the inertia associated with mesh motion.
Typically, prior FSI solutions involved solving a structures problem to calculate mesh movement.
Training Manual
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6. CFD Enhancements … ALE Formulation
Example: squeeze film
Note that the morphing algorithm, activated by the command FLDA,SOLU,ALE,T will operate on all nodes which are not constrained to have zero displacement.
The velocity vectors are being rescaled in each frame.
Training Manual
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7. CFD Enhancements … ALE Formulation
Example: torsional oscillation
Training Manual
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8. CFD Enhancements … ALE Formulation
Example: Comb drive problem - MEMS application
Mesh Deformation History
Rigid Body Translation
Training Manual
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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
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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
To maintain a suitable boundary layer mesh around the plate, one gives the same rotation to all the nodes not only on the plate, but near it as well. This facilitates the use of a quadrilateral mesh near the body, if necessary.
Constraining the motion of lines in the fluid helps the morphing algorithm maintain acceptable element shapes. This function is accomplished by macros and is necessary for large displacements.
Pressure
Velocity
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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
In this example, the analytical solution is based on assumptions that the plate is large, the gap is small, and the amplitude of the oscillation is fairly small.
Training Manual
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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
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13. 5.2 Surface Tension
CFD Enhancements

14. CFD Enhancements Surface 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
Tendency to Maintain a Surface Wetting Angle is a Characteristic of fluid and wall
CLEAR - VOF was added at 5.6.
Training Manual
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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
Activate as a solution option
FLDA,SOLU,SFTS,1
Surface Tension Coefficient
FLDA,NOMI,SFTS,value
Wetting Angle
FLDA,NOMI,WSCA,value
Training Manual
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16. CFD Enhancements … Surface Tension
Fluid in a Spinning Cylinder
Low Wetting Angle (5 deg) High Wetting Angle (175)
The surface tension coefficient is quite large in this case. If it were much smaller, the two cases would look more alike.
Training Manual
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17. CFD Enhancements … Surface Tension
Oscillating Water Droplet
There is no gravity in this case.
Training Manual
15 Aug 2000
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19. 5.3 Radiation in FLOTRAN
CFD Enhancements

20. CFD Enhancements Radiation 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
15 Aug 2000
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21. 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
15 Aug 2000
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22. 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
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23. 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
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24. 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
STEF : Stefan Boltzman constant (Defaults to 1.19E-11)
STEF, VALUE
TOFFST : Temperature offset (Defaults to 0)
TOFF, VALUE
RADOPT : Options for radiosity solver
RADOPT, FLUXRELX, FLUXTOL, SOLVER, MAXITER, TOLER, OVERRLEX
FLUXRELX : relaxation for radiosity flux (defaults to 0.1)
FLUXTOL : tolerance for radiosity flux (defaults to )
SOLVE: solver for radiation flux calculation
iterative = 0 (default)
direct = 1
MAXITER : maximum # of iterations for iterative solver (defaults to 1000)
TOLER : tolerance for iterative solver (defaults to 0.1)
OVERRELAX: relaxation for iterative solver (defaults to 0.1)
SPCTEMP : Space temperature for open enclosure
SPCTEMP, ENCL #, VALUE
SPCNOD : Space node number for open enclosure
SPCNOD, ENCL #, NODE #
Training Manual
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25. 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
HEMIOPT : Resolution for 3D view factor calculation
HEMIOPT, HRES (defaults to 10)
V2DOPT : Option for 2D view factor calculation
V2DOPT, GEOM, NDIV, HIDOPT, NZONE
GEOM: 0 or 1 (plane or axisymmetric)
NDIV : number of divisions for axisymmetric geometry (defaults to 20)
HIDOPT: 0 or 1 ( hidden or non-hidden option for view factor calculation)
NZONE : number of zones for hidden option (defaults to 200)
VFOPT: Option for view factor calculation
VFOPT, OPT
OPT = NEW : Compute new view factors
OPT = OLD : Use View factors in database
OPT = READ : Read view factors from file
VFCALC : Calculate view factors
VFCALC, Fname, Ext, Dir (defaults to jobname.vf)
VFQUERY :
VFQUERY, TARELEM, SRCELEM
TARELEM selected target elements
SRCELEM selected source elements.
Training Manual
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26. 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
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27. 5.4 Algebraic Solver
CFD Enhancements

28. CFD Enhancements Algebraic 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
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29. CFD Enhancements Algebraic Solver
GUI implementation
Commands
FLDATA,METH,dof,6
FLDATA,PBCG,FILL,6 (default)
Method uses an approximate decomposition of the Matrix
The Fill is the number of extra elements allowed compared to the sparsity pattern of the Matrix.
FLDA,SRCH,dof,2 (default)
Number of search vectors kept
Training Manual
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31. 5.5 Interpolation
CFD Enhancements

32. CFD Enhancements Interpolation
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
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33. CFD Enhancements … Interpolation
Access Refinement
Through Mesh Tool
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34. CFD Enhancements … Interpolation
50 global
Iterations
Result of 5 more global iterations on the new mesh
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35. CFD Enhancements … Interpolation
Training Manual
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36. CFD Enhancements … Interpolation
900 global iterations
20 more G.I.
The mesh refinement was done with the MeshTool refinement feature. Elements were picked via defining a polygon which rather loosely enclosed the shock wave location.
The most refinement occurred near the axisymmetic centerline (x axis). The pressure contours are noticeably denser. The effect is there, but less pronounced, farther from the body.
Refinement of the solution took relatively few global iterations.
Pressure contours - shock
wave now sharper near the body!
Training Manual
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37. 5.6 Tabular Boundary Conditions
CFD Enhancements

38. CFD Enhancements Tabular 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
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39. CFD Enhancements … Tabular Boundary Conditions
Applications:
Drive ALE moving boundary problems.
Time varying flow for transients
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40. CFD Enhancements … Tabular Boundary Conditions
Dialog Boxes for DL, DA, D commands have changed!
Choice could be existing table...
Also may create table
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41. CFD Enhancements … Tabular Boundary Conditions
Name the table and its rows, columns and planes
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42. CFD Enhancements … Tabular Boundary Conditions
Fill it in…. Flow versus Time
Training Manual
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43. CFD Enhancements … Tabular Boundary Conditions
Compressiblity of the fluid is responsible for the overshoot of the outlet velocity curve.
Training Manual
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45. 5.7 FSI Macro FSSOLV
CFD Enhancements

46. CFD Enhancements FSI 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
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47. 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
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48. CFD Enhancements … FSI Macro FSSOLV
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49. CFD Enhancements … FSI Macro FSSOLV
Access “Physics” from PREP7 or SOLU:
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50. CFD Enhancements … FSI Macro FSSOLV
Training Manual
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51. 5.8 AUX3
CFD Enhancements

52. AUX3 provides a results file editing capability
CFD Enhancements AUX3
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
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53. Commands - No GUI! FILE,filename,extension,directory
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
ADDF,filename,extention,directory
combines results files
MODIFY,set,lstep,iter,Cumit,time,klevel
Changes set information
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