5. CFD Enhancements
CFD Enhancements
5.1 ALE (Arbitrary Lagrangian Eulerian) Formulation
• The fluid mesh may now have prescribed movement
• 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
NEW FEATURES 5.7
5.2 Surface Tension Effects
• 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
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5.1 ALE Formulation
CFD Enhancements
CFD Enhancements
ALE Formulation
• ALE - Arbitrary Lagrangian Eulerian formulation for
CFD analyses
– 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
NEW FEATURES 5.7
• Typical ANSYS Applications
• Interpretation and manipulation of FLOTRAN results data
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CFD Enhancements
… ALE Formulation
• ALE allows for deforming/moving fluid domains
• 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
NEW FEATURES 5.7
• Nodes are allowed to move in space to
accommodate moving bodies
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CFD Enhancements
… ALE Formulation
• Example: squeeze film
NEW FEATURES 5.7
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CFD Enhancements
… ALE Formulation
• Example: torsional oscillation
NEW FEATURES 5.7
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CFD Enhancements
… ALE Formulation
• Example: Comb drive problem - MEMS application
Rigid Body Translation
NEW FEATURES 5.7
Mesh Deformation History
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CFD Enhancements
… ALE Formulation
• Limitations in ANSYS 5.7:
– Incompressible flows and adiabatic compressible flows
– 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
NEW FEATURES 5.7
– Cartesian XY and axisymmetric in 2D
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CFD Enhancements
… ALE Formulation
• Constraining the motion of nodes
Pressure
Velocity
NEW FEATURES 5.7
Boundary layer
capturing box: all
nodes in the box
are moved along
with the plate
surface
Motion
constrained
on lines
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CFD Enhancements
… ALE Formulation
Squeeze film problem - circular plate
r=0
r=R
Pressure=P0
NEW FEATURES 5.7
Fixed Wall
h0
t=0
Moving wall
t=5
t=10
Mesh Deformation
History
Static Pressure
Contours History
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CFD Enhancements
… ALE Formulation
Squeeze film problem (cont'd)
• Analytical Result
– Assumption is h/R << 1(negligible inertia)
• FLOTRAN Results
– At t=10: Pressure = 42,828 (h/R->0.01)
NEW FEATURES 5.7
– Pressure force on moving plate =
1.5*p*m*(1/h**3)*dh/dt*R**4 = 42,411
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5.2 Surface Tension
CFD Enhancements
CFD Enhancements
Surface Tension
• CLEAR - VOF Formulation
– Computational Lagrangian Eulerian Advection Remap - Volume Of
Fluid
NEW FEATURES 5.7
– 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
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CFD Enhancements
… Surface Tension
• Applications
– Ink-Jet printers
– Micro-fluid handling (MEMS devices)
• Input
– Surface Tension Coefficient
– Wetting Angle (defaults to 90 degrees)
NEW FEATURES 5.7
– Mold Filling
• Normal to Surface
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CFD Enhancements
… Surface Tension
Fluid in a Spinning Cylinder
Low Wetting Angle (5 deg)
High Wetting Angle (175)
NEW FEATURES 5.7
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CFD Enhancements
… Surface Tension
Oscillating Water Droplet
NEW FEATURES 5.7
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5.3 Radiation in FLOTRAN
CFD Enhancements
CFD Enhancements
Radiation in FLOTRAN
• Generalized radiation analysis with two or more
radiating surfaces for FLUID141 and 142
• Features:
– Radiation solution using radiosity method
– Temperature dependent emissivity
– Multiple open/closed enclosures
NEW FEATURES 5.7
• Supported only for incompressible flow thermal
analysis
– Radiation analysis does NOT support symmetry BC's
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CFD Enhancements
… Radiation in FLOTRAN
• Features (cont'd):
– 3-D radiation analysis
• 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
NEW FEATURES 5.7
• View factor calculation using the Hemicube method
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CFD Enhancements
… Radiation in FLOTRAN
Procedure:
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)
NEW FEATURES 5.7
1. Define radiating surfaces using SF family of
commands
• Negative number for radiation into the element (for fluid
elements)
• All surfaces seeing each other should have the same
enclosure number
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CFD Enhancements
… Radiation in FLOTRAN
Procedure (cont'd):
2. Activate thermal analysis option
3. Define FLOTRAN analysis options
– Define material properties for solid and fluid elements
– Define reference conditions for temperature
NEW FEATURES 5.7
– FLDATA, SOLU, TEMP,1
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CFD Enhancements
… Radiation in FLOTRAN
Procedure (cont'd):
4. Define radiosity method options
– 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
NEW FEATURES 5.7
– Define Stefan Boltzsman constant STEF & temperature
offset TOFFST
• Define view factor calculation option VFOPT
• RDSF BC's are only supported for wall type boundaries
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CFD Enhancements
… Radiation in FLOTRAN
Procedure (cont'd):
5. Calculate & query view factors
• 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
NEW FEATURES 5.7
– Calculate view factors VFCALC
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CFD Enhancements
… Radiation in FLOTRAN
Procedure (cont'd):
6. Postprocessing
• 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
NEW FEATURES 5.7
– Output for radiation heat flow is turned on by default for
thermal analysis in FLOTRAN with surface radiation
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5.4 Algebraic Solver
CFD Enhancements
CFD Enhancements
Algebraic Solver
• PBCGM
– Preconditioned Bi-Conjugate Gradient Method
– 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
NEW FEATURES 5.7
• Also known as Bi-CGSTAB
• Usage
– User specifies Fill, number of search vectors
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CFD Enhancements
Algebraic Solver
• GUI implementation
NEW FEATURES 5.7
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5.5 Interpolation
CFD Enhancements
CFD Enhancements
Interpolation
• Think the mesh is too coarse in only one small
area?
• 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
NEW FEATURES 5.7
– Recirculation region, shock wave, etc.
– Note - you should save copies of the original database and
results file.
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CFD Enhancements
… Interpolation
NEW FEATURES 5.7
Access Refinement
Through Mesh Tool
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CFD Enhancements
… Interpolation
NEW FEATURES 5.7
50 global
Iterations
Result of 5 more global iterations on the new mesh
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CFD Enhancements
… Interpolation
NEW FEATURES 5.7
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CFD Enhancements
… Interpolation
20 more
G.I.
Pressure contours - shock
wave now sharper near
the body!
NEW FEATURES 5.7
900 global
iterations
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5.6 Tabular Boundary
Conditions
CFD Enhancements
CFD Enhancements
Tabular Boundary Conditions
• Tabular boundary conditions are now available for
the FLOTRAN DOF
• 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
NEW FEATURES 5.7
– VX,VY,VZ,PRES,TEMP,ENKE,ENDS,SP01….SP06
• ALE Analysis of a Simplified Torsional Mirror
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CFD Enhancements
… Tabular Boundary Conditions
• Applications:
– Drive ALE moving boundary problems.
NEW FEATURES 5.7
– Time varying flow for transients
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CFD Enhancements
… Tabular Boundary Conditions
• Choice could be
existing table...
• Also may create
table
NEW FEATURES 5.7
• Dialog Boxes for
DL, DA, D
commands have
changed!
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CFD Enhancements
… Tabular Boundary Conditions
NEW FEATURES 5.7
• Name the table
and its rows,
columns and
planes
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CFD Enhancements
… Tabular Boundary Conditions
• Fill it in…. Flow versus Time
NEW FEATURES 5.7
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CFD Enhancements
… Tabular Boundary Conditions
NEW FEATURES 5.7
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5.7 FSI Macro FSSOLV
CFD Enhancements
CFD Enhancements
FSI Macro FSSOLV
• Creates a recursive loop for Fluid Structure
Interaction (FSI) problems.
– 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.
NEW FEATURES 5.7
• Based on the use of Physics files
• Convergence: rate of change between loop passes
– Force & moment (INTSRF) - based on fluid physics
– Displacement - based on structural physics
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CFD Enhancements
… FSI Macro FSSOLV
• Example: flow over a “cement wall” (but Elasticity
reduced by 100 to create larger displacement….)
– 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.
NEW FEATURES 5.7
– Morphed region in red boxes
• Lines or areas that are shared by regions not to be
morphed will remain unchanged.
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CFD Enhancements
… FSI Macro FSSOLV
NEW FEATURES 5.7
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CFD Enhancements
… FSI Macro FSSOLV
• Access “Physics” from PREP7 or SOLU:
NEW FEATURES 5.7
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CFD Enhancements
… FSI Macro FSSOLV
NEW FEATURES 5.7
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5.8 AUX3
CFD Enhancements
CFD Enhancements
AUX3
• AUX3 provides a results file editing capability
– Works on all ANSYS results files
– No GUI
• Functions
– Eliminate sets of results from .rfl file
– Combine two results files
• take some sets from each file
NEW FEATURES 5.7
– Enables control of size of result file!
– List Function
• Which exist
• Which marked for deletion
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CFD Enhancements
… AUX3
• Commands - No GUI!
– FILE,filename,extension,directory
– 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
NEW FEATURES 5.7
• Identifies the file to be operated on
– COMPRESS
• Executes the deletion of sets so indicated
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