5. CFD Enhancements

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

5.1 ALE Formulation CFD Enhancements

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 001419 15 Aug 2000 5-4

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 001419 15 Aug 2000 5-5

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 001419 15 Aug 2000 5-6

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

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

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

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 Training Manual 001419 15 Aug 2000 5-10

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 001419 15 Aug 2000 5-11

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

5.2 Surface Tension CFD Enhancements

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 001419 15 Aug 2000 5-14

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 001419 15 Aug 2000 5-15

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 001419 15 Aug 2000 5-16

CFD Enhancements … Surface Tension Oscillating Water Droplet There is no gravity in this case. Training Manual 001419 15 Aug 2000 5-17

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 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

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

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

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

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 0.0001) 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 001419 15 Aug 2000 5-24

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 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 001419 15 Aug 2000 5-25

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

5.4 Algebraic Solver CFD Enhancements

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 001419 15 Aug 2000 5-28

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 001419 15 Aug 2000 5-29

5.5 Interpolation CFD Enhancements

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 001419 15 Aug 2000 5-32

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

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

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

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 001419 15 Aug 2000 5-36

5.6 Tabular Boundary Conditions CFD Enhancements

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 001419 15 Aug 2000 5-38

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

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

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

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

CFD Enhancements … Tabular Boundary Conditions Compressiblity of the fluid is responsible for the overshoot of the outlet velocity curve. Training Manual 001419 15 Aug 2000 5-43

5.7 FSI Macro FSSOLV CFD Enhancements

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 001419 15 Aug 2000 5-46

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

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

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

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

5.8 AUX3 CFD Enhancements

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 001419 15 Aug 2000 5-52

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 Training Manual 001419 15 Aug 2000 5-53