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Old   September 8, 2006, 02:39
Default about compresive phase
  #1
James
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when I model the multiphase of water and air,as I need to set the pressure at the inlet,such error come out:

Notice This is a multiphase simulation with a compressible phase. Total pressure (used for post-processing or if total pressure is specified at a boundary) is calculated assuming all phases are incompressible.

What should I do to deal with it,if I insist to set the pressure of inlet ?any suggestion will be appreciated.
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Old   September 8, 2006, 06:11
Default Re: about compresive phase
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Joe
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Its unlikely that you should be setting the gaseous phase as compresible in the first place.
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Old   September 8, 2006, 07:47
Default Re: about compresive phase
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Robin
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How do you figure that Joe?
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Old   September 8, 2006, 12:43
Default Re: about compresive phase
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Joe
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A typical tank sloshing flow is hardly going to result in signifciant compression effects in the gaeous phase ...
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Old   September 8, 2006, 14:07
Default Re: about compresive phase
  #5
Robin
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...if you are simulating tank sloshing. James said nothing of the sort.
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Old   September 8, 2006, 15:14
Default Re: about compresive phase
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Joe
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To be precise, he didnt bother to specify his problem at all. An all to common occurance here. Hence my question ...
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Old   September 8, 2006, 15:17
Default Re: about compresive phase
  #7
Joe
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Correction, he did mention it was a tank sloshing problem: http://www.cfd-online.com/Forum/cfx.cgi?read=16846

I'll posed questions spread over multiple posts ... and people wonder why they dont get proper answers to their questions.

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Old   September 8, 2006, 20:05
Default Re: about compresive phase
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James
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Hi,Joe and Robin,

my model is compressible fluid as it is vacuum in the domain and with pressure at the inlet boundry condition.
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Old   September 11, 2006, 09:14
Default Re: about compresive phase
  #9
Robin
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Hi James,

All the message is doing is warning you that the post-processed value of Total Pressure is not calculated in the same manner as it would normally be for a compressible fluid. Just keep this in mind if you are interested in Total Pressure.

Now, having a vacuum may present other problems. You can't actually specify zero absolute pressure or the code will blow. If you have water coming into the domain, a low pressure (say 0.1 atmosphere) will probably do.

Let us know how it works out.

Regards, Robin
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Old   September 11, 2006, 21:00
Default Re: about compresive phase
  #10
James
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Hi,Robin In fact I simulate this to show the configuration of the flow in the counter Gravity filling.At first,I set the inlet using constant velocity of water.In order to close the reality,then the pressure of inlet will be included.The pressure is a constant ,but maybe because of the compressive fluid in the domain,it always goes wrong. I also set the inlet pressure as 10kpa or 30kpa,but it doesn't work ,either.Expect for your suggestion.Thanks.
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Old   September 12, 2006, 03:16
Default Re: about compresive phase
  #11
James
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I try to simulate my model by using the degassing mdel,set the air to dispersed fluid,and set the outlet the degssing boundry,and use the free surface to simulate it.By doing this air can flow out the doman,not the water,which is I expected.Is it feasible? It converges well,but in the post I cannot get the isoface of the volume fraction,for example,water volume fraction 0.5 .The pressure works well however.can you give me some help?My setting is : LIBRARY:

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 EXECUTION CONTROL:

PARALLEL HOST LIBRARY:

HOST DEFINITION: yuhuan

Installation Root = C:\Program Files\Ansys Inc\CFX\CFX-%v

Host Architecture String = intel_p4.sse2_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

END

END

RUN DEFINITION:

Definition File = D:/board02/board.def

Interpolate Initial Values = Off

Run Mode = Full

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 = 1

Start Method = Serial

END

END END FLOW:

DOMAIN: Domain 1

Coord Frame = Coord 0

Domain Type = Fluid

Fluids List = Air at 25 C,Water

Location = Assembly

BOUNDARY: inlet

Boundary Type = INLET

Location = INLET

BOUNDARY CONDITIONS:

FLOW REGIME:

Option = Subsonic

END

MASS AND MOMENTUM:

Option = Fluid Velocity

END

TURBULENCE:

Option = Medium Intensity and Eddy Viscosity Ratio

END

END

FLUID: Air at 25 C

BOUNDARY CONDITIONS:

VELOCITY:

Normal Speed = 0 [m s^-1]

Option = Normal Speed

END

VOLUME FRACTION:

Option = Value

Volume Fraction = 0

END

END

END

FLUID: Water

BOUNDARY CONDITIONS:

VELOCITY:

Normal Speed = 1 [m s^-1]

Option = Normal Speed

END

VOLUME FRACTION:

Option = Value

Volume Fraction = 1

END

END

END

END

BOUNDARY: outlet

Boundary Type = OUTLET

Location = TOP

BOUNDARY CONDITIONS:

FLOW REGIME:

Option = Subsonic

END

MASS AND MOMENTUM:

Option = Degassing Condition

END

END

END

BOUNDARY: wall

Boundary Type = WALL

Location = BOTTOM,SIDE

BOUNDARY CONDITIONS:

WALL INFLUENCE ON FLOW:

Option = No Slip

END

WALL ROUGHNESS:

Option = Smooth Wall

END

END

WALL CONTACT MODEL:

Option = Use Volume Fraction

END

END

BOUNDARY: symmtry

Boundary Type = SYMMETRY

Location = BACK,FRONT

END

DOMAIN MODELS:

BUOYANCY MODEL:

Buoyancy Reference Density = 997 [kg m^-3]

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

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

Gravity Z Component = -9.81 [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 = 10 [kPa]

END

END

FLUID: Air at 25 C

FLUID MODELS:

FLUID BUOYANCY MODEL:

Option = Density Difference

END

MORPHOLOGY:

Mean Diameter = 1 [mm]

Option = Dispersed 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:

Homogeneous Model = False

Option = None

END

THERMAL RADIATION MODEL:

Option = None

END

TURBULENCE MODEL:

Homogeneous Model = On

Option = k epsilon

BUOYANCY TURBULENCE:

Option = None

END

END

TURBULENT WALL FUNCTIONS:

Option = Scalable

END

END

FLUID PAIR: Air at 25 C | Water

Surface Tension Coefficient = 0.073 [N m^-1]

INTERPHASE TRANSFER MODEL:

Option = Particle Model

END

MASS TRANSFER:

Option = None

END

MOMENTUM TRANSFER:

DRAG FORCE:

Option = Grace

Volume Fraction Correction Exponent = 4

END

LIFT FORCE:

Option = None

END

TURBULENT DISPERSION FORCE:

Option = Lopez de Bertodano

Turbulent Dispersion Coefficient = 0.1

END

VIRTUAL MASS FORCE:

Option = None

END

WALL LUBRICATION FORCE:

Option = None

END

END

SURFACE TENSION MODEL:

Option = None

END

TURBULENCE TRANSFER:

ENHANCED TURBULENCE PRODUCTION MODEL:

Option = Sato Enhanced Eddy Viscosity

END

END

END

MULTIPHASE MODELS:

Homogeneous Model = Off

FREE SURFACE MODEL:

Option = Standard

END

END

END

INITIALISATION:

Option = Automatic

FLUID: Air at 25 C

INITIAL CONDITIONS:

Velocity Type = Cartesian

CARTESIAN VELOCITY COMPONENTS:

Option = Automatic with Value

U = 0 [m s^-1]

V = 0 [m s^-1]

W = 1 [m s^-1]

END

VOLUME FRACTION:

Option = Automatic

END

END

END

FLUID: Water

INITIAL CONDITIONS:

Velocity Type = Cartesian

CARTESIAN VELOCITY COMPONENTS:

Option = Automatic with Value

U = 0 [m s^-1]

V = 0 [m s^-1]

W = 1 [m s^-1]

END

VOLUME FRACTION:

Option = Automatic with Value

Volume Fraction = 1

END

END

END

INITIAL CONDITIONS:

EPSILON:

Option = Automatic with Value

END

K:

Option = Automatic with Value

END

STATIC PRESSURE:

Option = Automatic with Value

Relative Pressure = 0 [Pa]

END

END

END

OUTPUT CONTROL:

RESULTS:

File Compression Level = Default

Option = Standard

Output Boundary Flows = All

END

TRANSIENT RESULTS: Transient Results 1

File Compression Level = Default

Include Mesh = No

Option = Selected Variables

Output Variables List = Absolute Pressure,Air at 25 C.Volume \

Fraction,Pressure,Water.Velocity,Water.Volume Fraction

Time Interval = 0.02 [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 = 0.01 [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 = 10

Timescale Control = Coefficient Loops

END

CONVERGENCE CRITERIA:

Residual Target = 1.E-4

Residual Type = RMS

END

TRANSIENT SCHEME:

Option = Second Order Backward Euler

END

END END COMMAND FILE:

Version = 10.0

Results Version = 10.0 END

Thank you.
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