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September 8, 2006, 02:39 
about compresive phase

#1 
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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 postprocessing 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. 

September 8, 2006, 06:11 
Re: about compresive phase

#2 
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Its unlikely that you should be setting the gaseous phase as compresible in the first place.


September 8, 2006, 07:47 
Re: about compresive phase

#3 
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How do you figure that Joe?


September 8, 2006, 12:43 
Re: about compresive phase

#4 
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A typical tank sloshing flow is hardly going to result in signifciant compression effects in the gaeous phase ...


September 8, 2006, 14:07 
Re: about compresive phase

#5 
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...if you are simulating tank sloshing. James said nothing of the sort.


September 8, 2006, 15:14 
Re: about compresive phase

#6 
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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 ...


September 8, 2006, 15:17 
Re: about compresive phase

#7 
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Correction, he did mention it was a tank sloshing problem: http://www.cfdonline.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. 

September 8, 2006, 20:05 
Re: about compresive phase

#8 
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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. 

September 11, 2006, 09:14 
Re: about compresive phase

#9 
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Hi James,
All the message is doing is warning you that the postprocessed 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 

September 11, 2006, 21:00 
Re: about compresive phase

#10 
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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.


September 12, 2006, 03:16 
Re: about compresive phase

#11 
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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 = 1.831E05 [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 = 2.61E02 [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 = 2.57E04 [K^1] ABSORPTION COEFFICIENT: Absorption Coefficient = 1.0 [m^1] Option = Value END DYNAMIC VISCOSITY: Dynamic Viscosity = 8.899E4 [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 = kway 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.E4 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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