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ANSYS Tutorial: CFX Re-MeshingANSYS CFX Tutorial: In ANSYS CFX 12.1 it is possible to apply automatic re-meshing using ANSYS IC! CF" #or cases $ith large mesh %e#ormation. &hisarticle e'plains the (ey steps to ma(e it $or(.

INTRODUCTION

In many CF" cases $here #or e'ample #lui% structure interaction )FSI* is use%+ large %e#ormation is ,erycommon. enerally+ CF" sol,ers allo$ #or a mesh %e#ormation to a%apt to this %e#ormation. o$e,er+ i#the %e#ormation is too large it might be har% to %e#orm the current mesh $ithout %estroying the mesh or atleast %istort the elements too much.&he metho% to o,ercome this problem is to apply a re-mesh step $hen the current mesh /uality becomestoo lo$. &his can be %one inANSYS CFX12.1 using the meshing capabilities in ANSYS IC! CF".

CREATING INPUT MESH

&his part nee%s to be %one in ANSYS IC! CF" as $e $ill use it #or the re-meshing process. In thise'ample+ I $ill let a rectangular bo' mo,e %o$n$ar%s in a s/uare channel.

Figure 1sho$s the geometry that is originally create% in ANSYS "esign!o%eler. First $e nee% to createparts #or the boun%aries $e $ant to use in our CF" simulation. &he bo' in the centre is target #or a

%o$n$ar% motion. It is gi,en the name BOX. As in any mesh session in IC! CF"+ you must apply yourre/uire% si0ing necessary #or the simulation.

Figure 1

http://www.edr.se/produkter/ansys_caepipe/ansys_cfdhttp://www.edr.se/produkter/ansys_caepipe/ansys_cfd

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&herea#ter+ bring up the Replay Managerin IC! CF" an% per#orm the %esire% meshing steps. Sa,ethese comman%s to a replay ).rpl* #ile #or later use in ANSYS CFX. Also+ e'port the create% mesh toANSYS CFX #ormat an% sa,e the proect an% remember the location o# the IC! CF" #iles ).tin an% .rpl*.

SET UP THE ANSYS CFX CASE.

GENERAL SETUP.

In this simple case+ the 3X $ill mo,e %o$n$ar%s $ith time.

"e#ine the #lui% #lo$ in the %omain $ith the %esire% physics an% allo$ #or mesh %e#ormation. Set the mesh sti##ness to increase in small ,olumes. &his $ill preser,e the small prismas close to

the soli% $alls as much as possible an% the main %e#ormation $ill be absorbe% #urther a$ay #rom the bo%y.

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oun%ary %etails

At the top an% bottom sur#aces+ opening con%itions is applie% so that #lui% can enter or lea,e the

%omain as nee%e%.&he #un%amental part in this case is to allo$ #or mesh %e#ormation an% monitor the /uality o# the mesh. Asthe /uality becomes too lo$ a re-mesh call is ma%e. &he motion o# the $alls is here %escribe% $ith ane'pression.

Create an e'pression that %escribe the motion o# the soli%. In this case a linear motion is use%

$hich increases $ith time. &he e'pression is name% to 4motion4. &he reason #or using Time This Runisthat I $ill other$ise get large umps $hen the sol,er restarts a#ter a re-mesh. Alternati,ely+ the ,ariablemesh reinitialisation time can be use%.

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Create the remaining boun%aries e'cept the mo,ing $all as usual an% set the mesh motion tounspeci#ie%. &his $ill allo$ #or the no%es on the sur#ace to mo,e i# nee%e%.

&he $all boun%ary on the 3X is some$hat %i##erent compare% to the other boun%aries. ere+ the motione'pression shoul% be set as the 0-a'is %isplacement. Since the bo' shoul% mo,e %o$n$ar%s a minus signis a%%e%.

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INTERUPT CONTROL SETUP.

&he ne't step is to set up a stop control that $ill monitor the mesh /uality an% stop the sol,er.

&he #irst step is to create a logical e'pression that monitors the orthogonality in the mesh. &he

e'pression is gi,en the name remeshingcond. &his e'pression $ill be 1 i# the orthogonality becomes lo$erthan 5 %egrees an% 6 i# not.

A%% the e'pression as in interrupt control un%er the sol,er control tab.

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Speci#y a con#iguration to allo$ #or special e,ents in the simulation. For e'ample a con#iguration

can allo$ #or a se/uence o# simulations or a re-mesh.

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RE-MESH CONTROL SETUP.

e#ore the re-meshing is %e#ine% t$o output monitors nee%s to be %e#ine%. &he reason #or this is that there-meshing #eature uses output monitors as input to ANSYS IC! CF".

&he #irst output control is a eometry Scale #actor. &his $ill scale the ANSYS CFX output to

match the mo%el in IC! CF". ere+ the geometry scale is set to 1mm as the IC! mo%el is %one in mm.I# the mo%el is create% in the same %imensions this is not nee%e%.

&he secon% output monitor is 7A88 "isplacement 0. &his output monitor trac(s the a,erage o#

the total centroi% %isplacement o# the mo,ing boun%ary. &his ,ariable is a%%e% in ,ersion 12 an% trac(s thecentroi% o# a sur#ace #rom the start o# the simulation. &hus+ the monitor $ill gi,e us the total motion o# thebo%y #rom the #irst time step o# the simulation.

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7ith these t$o output controls %e#ine% $e can no$ speci#y our re-meshing.

Create a ne$ re-mesh $ith the option IC! CF" 9eplay.

&he re-mesh shoul% be acti,ate% by our pre,iously create% interrupt con%ition.

&he %omain that shoul% be meshe% is here 3"Y. o%y correspon%s to the ,olume in IC!

CF".

&he geometry #ile shoul% be the .tin #ile create% %uring the meshing.

&he replay is the # ile that stores the meshing steps %one %uring meshing.

&he ne't step is to create an IC! CF" art !ap. &his couples the boun%ary in ANSYS CFX tocorrespon%ing boun%ary in IC! CF". In this case+ $e only nee% to create one part map since $e onlyha,e one mo,ing boun%ary.Finally+ t$o scalar parameters nee%s to be create%. &he name o# these scalar parameters are sensiti,e asthey are i%enti#ie% by the re-meshing scripts inclu%e% in the ANSYS CFX installation.

&he #irst one is name% "IS8AC!N& ; 3X an% shoul% use the 7A88 "isplacement 0

monitor pre,iously %e#ine%.

&he secon% scalar parameter shoul% be name% IC! CF" eometry Scale an% shoul% be set to

the correspon%ing monitor point.

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&his is $hat shoul% be nee%e% to per#orm this type o# analysis. &he animation at the top sho$ the motion

o# the bo' through the %omain. asically+ the script that run the motion o# any part in IC! CF" can bemo%i#ie% to allo$ #or any %e#ormation. I# Y3< $ant to %o this an% nee% a%,ice or help. i,e us a call=

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