5. CFD Enhancements

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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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… ALE Formulation

• Example: squeeze film

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… 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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… 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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… 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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… 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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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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… 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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… Surface Tension

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

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… Surface Tension

Oscillating Water Droplet

5.3 Radiation in FLOTRAN

CFD Enhancements

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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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… 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

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… 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

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… 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

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… 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

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… 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

5.4 Algebraic Solver

CFD Enhancements

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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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Algebraic Solver

• GUI implementation

5.5 Interpolation

CFD Enhancements

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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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… Interpolation

Access Refinement Through Mesh Tool

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… Interpolation

50 globalIterations

Result of 5 more global iterations on the new mesh

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… Interpolation

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… 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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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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… Tabular Boundary Conditions

• Applications:

– Drive ALE moving boundary problems.

– Time varying flow for transients

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… 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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… Tabular Boundary Conditions

• Name the table and its rows, columns and planes

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… Tabular Boundary Conditions

• Fill it in…. Flow versus Time

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… Tabular Boundary Conditions

5.7 FSI Macro FSSOLV

CFD Enhancements

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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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… 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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… FSI Macro FSSOLV

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.7

• Access “Physics” from PREP7 or SOLU:

CFD Enhancements

… FSI Macro FSSOLV

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… FSI Macro FSSOLV

5.8 AUX3

CFD Enhancements

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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