i will try using your method. recently, i simulated a single bubble of quiescent water in a closed tank using vof model, however, i found the volume fraction of bubble is decreasing with increasing time, the interface of bubble is blurry,even to disappear, my mesh is very good and the number of the meshes in a bubble is about 20, i think the mesh is very enough, i do not know how to do ? anyone give me suggestion,thanks in advance. this is out file:

| | CFX Command Language for Run | | | +--------------------------------------------------------------------+

EXECUTION CONTROL:

RUN DEFINITION:

Definition File = D:/xjj/2mmbubble_009.res

Interpolate Initial Values = Off

Run Mode = Full

END

PARALLEL HOST LIBRARY:

HOST DEFINITION: b

Installation Root = C:\CFXb\CFX-%v

Host Architecture String = intel_pentium_winnt5.1

END

END

PARTITIONER STEP CONTROL:

Multidomain Option = Independent Partitioning

Runtime Priority = Standard

MEMORY CONTROL:

Memory Allocation Factor = 1.0

END

PARTITIONING TYPE:

MeTiS Type = k-way

Option = MeTiS

Partition Size Rule = Automatic

Partition Weight Factors = 0.500, 0.500

END

END

SOLVER STEP CONTROL:

Runtime Priority = Standard

EXECUTABLE SELECTION:

Double Precision = Off

END

MEMORY CONTROL:

Memory Allocation Factor = 1.0

END

PARALLEL ENVIRONMENT:

Number of Processes = 2

Start Method = PVM Local Parallel

Parallel Host List = b*2

END

END END LIBRARY:

CEL:

EXPRESSIONS:

DenH = 1000 [kg m^-3]

DownH1 = 0.048 [m]

Rbubble1 = 0.001 [m]

dist1 = Rbubble1-sqrt((x-0.0025[m])^2+(z-0.002[m])^2)

UpVFbubble1 = step((dist1)/1[m])

UpVFwater1 = 1-UpVFbubble1

Pres1 = DenH*g*UpVFwater1*DownH1

END

END

MATERIAL: Air at 25 C

Material Description = Air at 25 C and 1 atm (dry)

Material Group = Air Data, Constant Property Gases

Option = Pure Substance

Thermodynamic State = Gas

PROPERTIES:

Option = General Material

Thermal Expansivity = 0.003356 [K^-1]

ABSORPTION COEFFICIENT:

Absorption Coefficient = 0.01 [m^-1]

Option = Value

END

DYNAMIC VISCOSITY:

Dynamic Viscosity = 1.831E-05 [kg m^-1 s^-1]

Option = Value

END

EQUATION OF STATE:

Density = 1.185 [kg m^-3]

Molar Mass = 28.96 [kg kmol^-1]

Option = Value

END

REFRACTIVE INDEX:

Option = Value

Refractive Index = 1.0 [m m^-1]

END

SCATTERING COEFFICIENT:

Option = Value

Scattering Coefficient = 0.0 [m^-1]

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Pressure = 1 [atm]

Reference Specific Enthalpy = 0. [J/kg]

Reference Specific Entropy = 0. [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 1.0044E+03 [J kg^-1 K^-1]

Specific Heat Type = Constant Pressure

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 2.61E-02 [W m^-1 K^-1]

END

END

END

MATERIAL: Water

Material Description = Water (liquid)

Material Group = Water Data, Constant Property Liquids

Option = Pure Substance

Thermodynamic State = Liquid

PROPERTIES:

Option = General Material

Thermal Expansivity = 2.57E-04 [K^-1]

ABSORPTION COEFFICIENT:

Absorption Coefficient = 1.0 [m^-1]

Option = Value

END

DYNAMIC VISCOSITY:

Dynamic Viscosity = 8.899E-4 [kg m^-1 s^-1]

Option = Value

END

EQUATION OF STATE:

Density = 997.0 [kg m^-3]

Molar Mass = 18.02 [kg kmol^-1]

Option = Value

END

REFRACTIVE INDEX:

Option = Value

Refractive Index = 1.0 [m m^-1]

END

SCATTERING COEFFICIENT:

Option = Value

Scattering Coefficient = 0.0 [m^-1]

END

SPECIFIC HEAT CAPACITY:

Option = Value

Reference Pressure = 1 [atm]

Reference Specific Enthalpy = 0.0 [J/kg]

Reference Specific Entropy = 0.0 [J/kg/K]

Reference Temperature = 25 [C]

Specific Heat Capacity = 4181.7 [J kg^-1 K^-1]

Specific Heat Type = Constant Pressure

END

THERMAL CONDUCTIVITY:

Option = Value

Thermal Conductivity = 0.6069 [W m^-1 K^-1]

END

END

END END FLOW:

DOMAIN: Domain 1

Coord Frame = Coord 0

Domain Type = Fluid

Fluids List = Air at 25 C,Water

Location = Assembly

BOUNDARY: out

Boundary Type = OPENING

Location = OUTLET

BOUNDARY CONDITIONS:

FLOW DIRECTION:

Option = Normal to Boundary Condition

END

FLOW REGIME:

Option = Subsonic

END

MASS AND MOMENTUM:

Option = Opening Pressure and Direction

Relative Pressure = 0 [Pa]

END

END

FLUID: Air at 25 C

BOUNDARY CONDITIONS:

VOLUME FRACTION:

Option = Value

Volume Fraction = 1

END

END

END

FLUID: Water

BOUNDARY CONDITIONS:

VOLUME FRACTION:

Option = Value

Volume Fraction = 0

END

END

END

END

BOUNDARY: Domain 1 Default

Boundary Type = WALL

Location = INLET,SURFS A,SURFS B

BOUNDARY CONDITIONS:

WALL INFLUENCE ON FLOW:

Option = No Slip

END

END

FLUID PAIR: Air at 25 C | Water

BOUNDARY CONDITIONS:

WALL ADHESION:

Option = None

END

END

END

END

BOUNDARY: sym1

Boundary Type = SYMMETRY

Location = FRONT

END

BOUNDARY: sym2

Boundary Type = SYMMETRY

Location = BACK

END

DOMAIN MODELS:

BUOYANCY MODEL:

Buoyancy Reference Density = 1.3 [kg m^-3]

Gravity X Component = 0 [m s^-2]

Gravity Y Component = 0 [m s^-2]

Gravity Z Component = -9.8 [m s^-2]

Option = Buoyant

BUOYANCY REFERENCE LOCATION:

Option = Automatic

END

END

DOMAIN MOTION:

Option = Stationary

END

MESH DEFORMATION:

Option = None

END

REFERENCE PRESSURE:

Reference Pressure = 1 [atm]

END

END

FLUID: Air at 25 C

FLUID MODELS:

FLUID BUOYANCY MODEL:

Option = Density Difference

END

MORPHOLOGY:

Option = Continuous Fluid

END

END

END

FLUID: Water

FLUID MODELS:

FLUID BUOYANCY MODEL:

Option = Density Difference

END

MORPHOLOGY:

Option = Continuous Fluid

END

END

END

FLUID MODELS:

COMBUSTION MODEL:

Option = None

END

HEAT TRANSFER MODEL:

Fluid Temperature = 25 [C]

Homogeneous Model = True

Option = Isothermal

END

THERMAL RADIATION MODEL:

Option = None

END

TURBULENCE MODEL:

Option = Laminar

END

END

FLUID PAIR: Air at 25 C | Water

Surface Tension Coefficient = 0.07256 [N m^-1]

INTERPHASE TRANSFER MODEL:

Option = Free Surface

END

MASS TRANSFER:

Option = None

END

SURFACE TENSION MODEL:

Option = Continuum Surface Force

Primary Fluid = Air at 25 C

Volume Fraction Smoothing Type = Volume-Weighted

END

END

MULTIPHASE MODELS:

Homogeneous Model = On

FREE SURFACE MODEL:

Option = Standard

END

END

END

INITIALISATION:

Option = Automatic

FLUID: Air at 25 C

INITIAL CONDITIONS:

VOLUME FRACTION:

Option = Automatic with Value

Volume Fraction = UpVFbubble1

END

END

END

FLUID: Water

INITIAL CONDITIONS:

VOLUME FRACTION:

Option = Automatic with Value

Volume Fraction = UpVFwater1

END

END

END

INITIAL CONDITIONS:

Velocity Type = Cartesian

CARTESIAN VELOCITY COMPONENTS:

Option = Automatic with Value

U = 0 [m s^-1]

V = 0 [m s^-1]

W = 0 [m s^-1]

END

STATIC PRESSURE:

Option = Automatic with Value

Relative Pressure = Pres1

END

END

END

OUTPUT CONTROL:

RESULTS:

File Compression Level = Default

Option = Standard

END

TRANSIENT RESULTS: Transient Results 1

File Compression Level = Default

Option = Standard

Time Interval = 0.002 [s]

END

END

SIMULATION TYPE:

Option = Transient

INITIAL TIME:

Option = Automatic with Value

Time = 0 [s]

END

TIME DURATION:

Option = Total Time

Total Time = 1 [s]

END

TIME STEPS:

Option = Timesteps

Timesteps = 0.0001 [s]

END

END

SOLUTION UNITS:

Angle Units = [rad]

Length Units = [m]

Mass Units = [kg]

Solid Angle Units = [sr]

Temperature Units = [K]

Time Units = [s]

END

SOLVER CONTROL:

ADVECTION SCHEME:

Option = High Resolution

END

CONVERGENCE CONTROL:

Maximum Number of Coefficient Loops = 15

Timescale Control = Coefficient Loops

END

CONVERGENCE CRITERIA:

Residual Target = 0.00001

Residual Type = RMS

END

TRANSIENT SCHEME:

Option = Second Order Backward Euler

END

END END COMMAND FILE:

Version = 10.0

Results Version = 10.0 END

+--------------------------------------------------------------------+ | | | Partitioning | | | +--------------------------------------------------------------------+

+--------------------------------------------------------------------+ | | | ANSYS CFX Partitioner 10.0 | | | | Version 2005.07.11-10.24 Mon Jul 11 10:26:04 GMTDT 2005 | | | | Executable Attributes | | | | single-32bit-optimised-supfort-noprof-nospag-lcomp | | | | Copyright 1996-2005 ANSYS Europe Ltd. | +--------------------------------------------------------------------+

+--------------------------------------------------------------------+ | Job Information | +--------------------------------------------------------------------+

Run mode: partitioning run

Host computer: B Job started: Thu Jan 10 10:18:41 2008

+--------------------------------------------------------------------+ | Memory Allocated for Run (Actual usage may be less) | +--------------------------------------------------------------------+

Data Type Kwords Words/Node Words/Elem Kbytes Bytes/Node

Real 2120.0 13.25 26.80 8281.2 53.00 Integer 6895.9 43.10 87.18 26937.0 172.40 Character 1997.4 12.48 25.25 1950.6 12.48 Logical 40.0 0.25 0.51 156.2 1.00 Double 949.7 5.94 12.01 7419.6 47.49

+--------------------------------------------------------------------+ | Total Number of Nodes, Elements, and Faces | +--------------------------------------------------------------------+

Domain Name : Domain 1

Total Number of Nodes = 160000

Total Number of Elements = 79101

Total Number of Hexahedrons = 79101

Total Number of Faces = 159998

+--------------------------------------------------------------------+ | Partitioning Information | +--------------------------------------------------------------------+

Partitioning of domain: Domain 1

- Partitioning tool: MeTiS multilevel weighted k-way algorithm - Number of partitions: 2 - Number of graph-nodes: 160000 - Number of graph-edges: 796400

Partitioning information for domain: Domain 1

+-----------+---------------------+-----------+--------+

| Elements | Vertices (Overlap) | Faces | Weight | +-------------+-----------+---------------------+-----------+--------+ | Full mesh | 79101 | 160000 | 159998 | | +-------------+-----------+---------------------+-----------+--------+ | Part. 1 | 39631 | 80274 0.3% | 80155 | 0.500 | | Part. 2 | 39587 | 80198 0.3% | 80079 | 0.500 | +-------------+-----------+---------------------+-----------+--------+ | Sum of part.| 79218 | 160472 0.3% | 160234 | 1.000 | +-------------+-----------+---------------------+-----------+--------+

CPU-Time requirements:

- Preparations 1.406E-01 seconds - Low-level mesh partitioning 9.375E-02 seconds - Global partitioning information 3.125E-02 seconds - Vertex, element and face partitioning information 9.375E-02 seconds - Element and face set partitioning information 4.688E-02 seconds - Summed CPU-time for mesh partitioning 9.219E-01 seconds

+--------------------------------------------------------------------+ | Job Information | +--------------------------------------------------------------------+

Host computer: B Job finished: Thu Jan 10 10:18:44 2008 Total CPU time: 1.516E+00 seconds

or: ( 0: 0: 0: 1.516 )

( Days: Hours: Minutes: Seconds )

Total wall clock time: 3.000E+00 seconds

or: ( 0: 0: 0: 3.000 )

( Days: Hours: Minutes: Seconds )

+--------------------------------------------------------------------+ | | | Solver | | | +--------------------------------------------------------------------+

+--------------------------------------------------------------------+ | | | ANSYS CFX Solver 10.0 | | | | Version 2005.07.11-10.24 Mon Jul 11 10:26:04 GMTDT 2005 | | | | Executable Attributes | | | | single-32bit-optimised-supfort-noprof-nospag-lcomp | | | | Copyright 1996-2005 ANSYS Europe Ltd. | +--------------------------------------------------------------------+

+--------------------------------------------------------------------+ | Job Information | +--------------------------------------------------------------------+

Run mode: parallel run (PVM)

Host computer: B Par. Process: Master running on mesh partition: 1 Job started: Thu Jan 10 10:18:45 2008

Host computer: B Par. Process: Slave running on mesh partition: 2 Job started: Thu Jan 10 10:18:45 2008

+--------------------------------------------------------------------+ | Memory Allocated for Run (Actual usage may be less) | +--------------------------------------------------------------------+

Allocated storage in: Kwords

Words/Node

Words/Elem

Kbytes

Bytes/Node

Partition | Real | Integer | Character| Logical | Double ----------+------------+------------+----------+----------+----------

1 | 37987.2 | 6495.2 | 2447.4 | 40.0 | 957.2

| 473.22 | 80.91 | 30.49 | 0.50 | 11.92

| 958.52 | 163.89 | 61.75 | 1.01 | 24.15

| 148387.6 | 25371.8 | 2390.0 | 39.1 | 7478.2

| 1892.88 | 323.65 | 30.49 | 0.50 | 95.39 ----------+------------+------------+----------+----------+----------

2 | 37941.5 | 6487.8 | 2447.4 | 40.0 | 957.2

| 473.10 | 80.90 | 30.52 | 0.50 | 11.94

| 958.43 | 163.89 | 61.82 | 1.01 | 24.18

| 148209.1 | 25342.8 | 2390.0 | 39.1 | 7478.2

| 1892.39 | 323.59 | 30.52 | 0.50 | 95.48 ----------+------------+------------+----------+----------+----------

Total | 75928.8 | 12982.9 | 4894.8 | 80.0 | 1914.4

| 474.55 | 81.14 | 30.59 | 0.50 | 11.97

| 959.90 | 164.13 | 61.88 | 1.01 | 24.20

| 296596.8 | 50714.6 | 4780.1 | 78.1 | 14956.4

| 1898.22 | 324.57 | 30.59 | 0.50 | 95.72 ----------+------------+------------+----------+----------+----------

+--------------------------------------------------------------------+ | Total Number of Nodes, Elements, and Faces | +--------------------------------------------------------------------+

Domain Name : Domain 1

Total Number of Nodes = 160000

Total Number of Elements = 79101

Total Number of Hexahedrons = 79101

Total Number of Faces = 159998

+--------------------------------------------------------------------+ | Buoyancy Reference Information | +--------------------------------------------------------------------+

Domain Group: Domain 1

Buoyancy has been activated. The absolute pressure will include

hydrostatic pressure contribution, using the following reference

coordinates: ( 2.50000E-03, 5.00000E-05, 5.00000E-02).

+--------------------------------------------------------------------+ | Initial Conditions Supplied by Fields in the Input Files | +--------------------------------------------------------------------+

Domain Name : Domain 1

Absolute Pressure

Air at 25 C | Water.Curvature

Air at 25 C | Water.Interfacial Area Density

Air at 25 C | Water.Surface Tension Force.Bforce

Air at 25 C | Water.Unclipped Interfacial Area Density

Air at 25 C.Absolute Temperature

Air at 25 C.Buoyancy Force.Bforce

Air at 25 C.Conservative Volume Fraction

Air at 25 C.Conservative Volume Fraction.Gradient

Air at 25 C.Courant Number

Air at 25 C.Shear Strain Rate

Air at 25 C.Smoothed Volume Fraction

Air at 25 C.Smoothed Volume Fraction.Gradient

Air at 25 C.Static Enthalpy

Air at 25 C.Static Entropy

Air at 25 C.Superficial Velocity

Air at 25 C.Volume Fraction

Courant Number

Density

Density.Gradient

Pressure

Pressure.Gradient

Total Pressure

Volume Porosity

Volume of Finite Volumes

Water.Absolute Temperature

Water.Buoyancy Force.Bforce

Water.Conservative Volume Fraction

Water.Conservative Volume Fraction.Beta

Water.Conservative Volume Fraction.Gradient

Water.Courant Number

Water.Shear Strain Rate

Water.Static Enthalpy

Water.Static Entropy

Water.Superficial Velocity

Water.Velocity

Water.Velocity.Beta

Water.Velocity.Gradient

Water.Volume Fraction

+--------------------------------------------------------------------+ | Average Scale Information | +--------------------------------------------------------------------+

Domain Name : Domain 1

Global Length = 2.9240E-03

Minimum Extent = 1.0000E-04

Maximum Extent = 5.0000E-02

Air at 25 C.Density = 1.1850E+00

Air at 25 C.Dynamic Viscosity = 1.8310E-05

Air at 25 C.Velocity = 3.6057E-02

Air at 25 C.Advection Time = 8.1095E-02

Air at 25 C.RMS Courant Number = 7.6015E-02

Air at 25 C.Maximum Courant Number = 6.8045E-01

Air at 25 C.Reynolds Number = 6.8233E+00

Air at 25 C.Mass (Conservative) = 3.3265E-10

Air at 25 C.Mass (Normalised) = 3.3265E-10

Air at 25 C.Volume = 2.8072E-10

Air at 25 C.Volume Fraction = 1.1229E-02

Water.Density = 9.9700E+02

Water.Dynamic Viscosity = 8.8990E-04

Water.Velocity = 3.6057E-02

Water.Advection Time = 8.1095E-02

Water.RMS Courant Number = 7.5096E-02

Water.Maximum Courant Number = 4.9677E-01

Water.Reynolds Number = 1.1812E+02

Water.Mass (Conservative) = 2.4645E-05

Water.Mass (Normalised) = 2.4645E-05

Water.Volume = 2.4719E-08

Water.Volume Fraction = 9.8877E-01

Water.Wave Speed = 1.6928E-01

Water.Froude Number = 2.1300E-01

+--------------------------------------------------------------------+ | The Equations Solved in This Calculation | +--------------------------------------------------------------------+

Subsystem : Momentum and Mass

U-Mom-Bulk

V-Mom-Bulk

W-Mom-Bulk

P-Vol

Subsystem : Volume Fractions

Mass-Water

CFD Solver started: Thu Jan 10 10:19:42 2008

+--------------------------------------------------------------------+ | Convergence History | +--------------------------------------------------------------------+

Hi,

Some comments:

You may need to look at the interface sharpening method. There are a few options, I don't know which one is best.

You may want to change the default differencing scheme for the volume fraction equation. Try going to a higher order scheme.

These things are unlikely to make much difference if you simulation is set up properly but are worth checking: Try double precision, tighter convergence and/or smaller timesteps.

Glenn Horrocks

Hi

Try using CFX-11, as its VOF implementation is a lot better than in in CFX-10. If the relative motion between the phases is important, you may need to use an inhomogeneous multiphase model.

Also, if you are trying to capture the bubble accurately, you may need a finer mesh (look for papers by P Zwart - he is involved in writing the CFX vof model to get a better idea of required grid resolutions)

-latslosh.

Thanks,Glenn Horrocks,latslosh the suggestion is very good for me.

[rk_k67]

HI
Im trying to apply VOF on a free surface flow.can any one give me an idea of what to do ? I have not worked with VOF so i would appriciate if anyone could tell me where to find a turorial or a simple example of VOF applied on a free surface in ANSYS .

thank alot

[ghorrocks]

Hi,

First you should look at the flow over a bump tutorial. That's the place to start.

Before I give any suggestions can you describe what you are modelling? It will determine what is important.

Glenn Horrocks

[rk_k67]

thanks

where can i have a look at tutorial 7 (and the bump model) ?
where is it ?

[ckleanth]

Originally Posted by rk_k67

thanks

where can i have a look at tutorial 7 (and the bump model) ?
where is it ?

idealy before using cfx comersialy you should had completed the tutorials.

on windows you can quickly add a shortcut for a folder;
in the current folder you want to create a shortcut press twice the windows key and twice the enter key and you're done.

[rk_k67]

hi

in tuturiol 7 it has used symmetry.
but Im assuming to use VOF.
is there any vof examples anywhere?

thanks

[ghorrocks]

Hi,

???? Symmetry and free surfaces are totally different things. I seem to remember tutorial 7 uses symmetry and free surfaces.

Glenn Horrocks