5. CFD Enhancements. Training Manual 001419 15 Aug 2000 5-2 CFD Enhancements 5.1 ALE (Arbitrary Lagrangian Eulerian) Formulation The fluid mesh may now.

5. CFD Enhancements

Training Manual 00141915 Aug 2000

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.7CFD 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

5.1 ALE Formulation

CFD Enhancements


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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


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… 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


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.7CFD Enhancements

… ALE Formulation

• Example: squeeze film


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.7CFD Enhancements

… ALE Formulation

• Example: torsional oscillation


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… ALE Formulation

Mesh Deformation HistoryMesh Deformation History

Rigid Body Translation

• Example: Comb drive problem - MEMS application


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.7CFD 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


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.7

• Constraining the motion of nodes

PressurePressure VelocityVelocity

Boundary layer capturing box: all nodes in the box are moved along with the plate surface

Motionconstrainedon lines

CFD Enhancements

… ALE Formulation


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.7CFD Enhancements

… ALE Formulation

Squeeze film problem - circular plate

t=0

t=5

t=10

Mesh Deformation History

Static Pressure Contours History

h0

r=0 r=R

Moving wall

Fixed Wall Pressure=P0


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.7CFD 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)

5.2 Surface Tension

CFD Enhancements


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.7CFD 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

– Continuum Surface Force• Tendency to Maintain a Surface Wetting Angle is a Characteristic of

fluid and wall


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.7CFD 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


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.7CFD Enhancements

… Surface Tension

Fluid in a Spinning CylinderLow Wetting Angle (5 deg) High Wetting Angle (175)


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.7CFD Enhancements

… Surface Tension

Oscillating Water Droplet

5.3 Radiation in FLOTRAN

CFD Enhancements


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.7CFD 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


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… 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


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.7CFD Enhancements


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


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.7CFD Enhancements


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


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.7CFD Enhancements


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


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.7CFD Enhancements


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


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.7CFD Enhancements


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

5.4 Algebraic Solver

CFD Enhancements


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.7CFD 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


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.7CFD Enhancements

Algebraic Solver

• GUI implementation

5.5 Interpolation

CFD Enhancements


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.7CFD 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.


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.7CFD Enhancements

… Interpolation

Access Refinement Through Mesh Tool


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.7CFD Enhancements

… Interpolation

50 globalIterations

Result of 5 more global iterations on the new mesh


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.7CFD Enhancements

… Interpolation


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.7CFD Enhancements

… Interpolation

20 more G.I.

900 global iterations

Pressure contours - shockwave now sharper near the body!

5.6 Tabular Boundary Conditions

CFD Enhancements


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.7CFD 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


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.7CFD Enhancements

… Tabular Boundary Conditions

• Applications:

– Drive ALE moving boundary problems.

– Time varying flow for transients


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.7CFD Enhancements


• Dialog Boxes for DL, DA, D commands have changed!

• Choice could be existing table...

• Also may create table


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.7CFD Enhancements


• Name the table and its rows, columns and planes


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.7CFD Enhancements


• Fill it in…. Flow versus Time


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.7CFD Enhancements


5.7 FSI Macro FSSOLV

CFD Enhancements


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.7CFD 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


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.7CFD 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.


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.7CFD Enhancements



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.7

• Access “Physics” from PREP7 or SOLU:

CFD Enhancements



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.7CFD Enhancements


5.8 AUX3

CFD Enhancements


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.7CFD 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


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… 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

5. CFD Enhancements. Training Manual 001419 15 Aug 2000 5-2 CFD Enhancements 5.1 ALE (Arbitrary Lagrangian Eulerian) Formulation The fluid mesh may now.

Documents

cfd enhancements5

p0new features

surfacenew features

wallnew features

squeeze filmnew features

surface wetting angle

moving body

moving plate