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#1 |
Guest
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Hi, CFX users
I am trying to set boundary conditions of 'fully developed flow' at pipe inlet without preliminary calculation. How can I set the BC's. Thanks. |
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#2 |
Guest
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Hi,
you can set a mass flow boundary condition at the inlet with negative mass flux. The procedure is explained in the CFX4.x solver manual. |
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#3 |
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Thank you for your response. But, I still could not set a mass flow boundary condition at the inlet. I read the CFX4.2 solver manual carefully and tried to set a flow boundary condition with very simple one block pipe. Then I got a error message. I am a CFX beginner. So I do not know what is my mistake. Would you please explain the my mistake ?
>>CFX4 :>OPTIONS THREE DIMENSIONS BODY FITTED GRID CARTESIAN COORDINATES TURBULENT FLOW ISOTHERMAL FLOW INCOMPRESSIBLE FLOW STEADY STATE :>MODEL TOPOLOGY :>CREATE PATCH PATCH NAME 'ENTRANCE' BLOCK NAME 'SOLID 1' PATCH TYPE 'MASS FLOW BOUNDARY' LOW K :>CREATE PATCH PATCH NAME 'OUTLET' BLOCK NAME 'SOLID 1' PATCH TYPE 'PRESSURE BOUNDARY' HIGH K :>MODEL DATA :>PHYSICAL PROPERTIES >>FLUID PARAMETERS VISCOSITY 1.0000E-03 DENSITY 9.9800E+02 :>SOLVER DATA :>PROGRAM CONTROL MAXIMUM NUMBER OF ITERATIONS 200 MASS SOURCE TOLERANCE 1.0000E-06 :>MODEL BOUNDARY CONDITIONS :>MASS FLOW BOUNDARIES >>FLUX MASS FLOW SPECIFIED FLUXES -1.000000E+01 :>STOP CFX-4.2 started on Mon Dec 18 17:32:03 KST 2000 This job was run on : kngr The command line was: /CFX4.2/bin/runsolve4 -rel 4.2 -dir /TH2/th/hjukim/CFX4/o ri/con/geo/F1/tmp1/.cfx4_tmpdir -enviro 08 -c m08.fc -geom m01.geo -dynam >>CFX4 >>OPTIONS THREE DIMENSIONS BODY FITTED GRID CARTESIAN COORDINATES TURBULENT FLOW ISOTHERMAL FLOW INCOMPRESSIBLE FLOW STEADY STATE :>MODEL TOPOLOGY >>CREATE PATCH PATCH NAME 'ENTRANCE' BLOCK NAME 'SOLID 1' PATCH TYPE 'MASS FLOW BOUNDARY' LOW K >>CREATE PATCH PATCH NAME 'OUTLET' BLOCK NAME 'SOLID 1' PATCH TYPE 'PRESSURE BOUNDARY' HIGH K :>MODEL DATA >>PHYSICAL PROPERTIES >>FLUID PARAMETERS VISCOSITY 1.0000E-03 DENSITY 9.9800E+02 :>SOLVER DATA >>PROGRAM CONTROL MAXIMUM NUMBER OF ITERATIONS 200 MASS SOURCE TOLERANCE 1.0000E-06 :>MODEL BOUNDARY CONDITIONS PERMANENT WORKSPACE ALLOCATED TYPE TOTAL SET TOTAL USED REAL 2716160 814827 INTEGER 1358080 484175 CHARACTER 1049 371 >>MASS FLOW BOUNDARIES >>FLUX LINEAR SOLVER - BLOCK DEPENDENCY INFORMATION: PERCENTAGE OF WELL ORDERED BLOCKS 100.0000 ORDERING USED 1 ####> ERROR. THE >>STOP COMMAND HAS NOT BEEN READ THE COMMANDS MAY BE IN THE WRONG ORDER OR INCORRECTLY TYPED PLEASE CORRECT AND RE-SUBMIT THE JOB THE CFX-4 SOLVER HAS BEEN STOPPED BY SUBROUTINE OUTOPT CFX-4.2 finished on Mon Dec 18 17:32:17 KST 2000 |
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#4 |
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Hi,
if you are using the 4.2 version, first of all there is a bug, or a spelling mistake in the manual whatever you want. The keyword is "FLUXES" and not "FLUX" (this was fixed in the 4.3 version): :>MASS FLOW BOUNDARIES >>FLUXES MASS FLOW SPECIFIED FLUXES -1.0E+1 1.0E+1 Secondly you have to define group numbers for the inlet and outlet: :>MODEL TOPOLOGY :>MODIFY PATCH OLD PATCH NAME 'ENTRANCE' NEW PATCH NAME 'ENTRANCE' NEW PATCH TYPE 'MASS FLOW BOUNDARY' NEW PATCH GROUP NUMBER 1 OLD PATCH NAME 'OUTLET' NEW PATCH NAME 'OUTLET' NEW PATCH TYPE 'MASS FLOW BOUNDARY' NEW PATCH GROUP NUMBER 2 In the boundary condition set up the first group refers to -1.0 , the second to 1.0 and so on if you have more. Hope this helps Fabian |
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#5 |
Guest
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I'm mot quite sure anymore but it is possible to have only a MASS FLOW BOUNDARY and a PRESSURE BOUNDARY ? This combination looks a little strange to me.
Marat |
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#6 |
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For this question,if the inlet is a mass flux, the converenge is difficult.this is also not the mean of :fully developed flow inlet.; so it may be good to use inlet BC. then you only need keep the momentum as a constant. that is Ok
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#7 |
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Murtadh
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Hi all,
Is there any updates in newer versions of Ansys to solve this issue ? |
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#8 |
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Glenn Horrocks
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Those original posts date from over 20 years ago, and back then the current version of CFX was CFX-4. It was a completely different solver and has little in common with the current solver. So this post is not relevant to the current solver.
There are several ways of getting a better approximation of fully developed flow at a boundary condition. The easiest is to use a pressure boundary.
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Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. |
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#9 | |
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Murtadh
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