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Setting the height of the stream in the free channel 

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July 9, 2015, 11:23 
Setting the height of the stream in the free channel

#1 
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kevin
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hello again,
I am doing a project on flow around a surface piercing cylinder. I carried out an experiment to measure the height of the water in the channel, the height of the flow when it rises up at the front of the cylinder and dips down around the sides and back of the cylinder. The results were: free stream height=80mm wave height at front of cylinder=81mm side(90 degrees)=76mm back=75mm The velocity of the flume was 0.21m and the width of the flume was 120mm. I used the CFX tutorial on flow over a bump to try and learn how to carry out this problem. I got all the basic steps in and used the expressions: Name Definition UpH 0.08[m] DownH 0.08 [m] DownPres DenH*g*DownVFWater*(DownHy)DenWater 997 [kg m^3] DenRef 1.185 [kg m^3] DenH (DenWater  DenRef ) UpVFAir step((yUpH)/1[m]) UpVFWater 1UpVFAir UpPres DenH*g*UpVFWater*(UpHy) DownVFAir step((yDownH)/1[m]) DownVFWater 1DownVFAir The only things I changed from the tutorial were the upstream and downstream heights. The domain I'm using is 1m long and 120mm wide. I was wondering why when I run the results the flow seems to come in to the inlet boundary at the correct height of 80mm but then dips down dramatically before it develops up to the cylinder were the action happens. The results I was looking to achieve were the pressure profile of the cylinder, the height of the isosurface around the cylinder and the Cd of the cylinder. Any help or guidance would be much appreciated. Thanks for your time. Regards, Kevin McCartin Undergraduate Mech Engineering, Institute of technology Tallaght PS: I have my file saved as an ANSYS workbench file but it will not allow me to attach it? 

July 9, 2015, 18:58 

#2 
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Glenn Horrocks
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Please post your CCL (that's just a small text file) and an image of what you are modelling.


July 9, 2015, 20:34 

#3 
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kevin
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Ghorrocks,
Thanks for your help and time it is much appreciated. I am not sure how to access the ccl file.I am presuming it is the .out file on ANSYS workbench 15 as it is a text file. I have attached 3 photos in a word document also to try show the situation a little better. As you will see from the photo at the inlet boundary the flow suddenly drops. Maybe there is a problem with the expressions used further upstream. Thanks again. Kevin McCartin Mechanical engineering undergraduate, Institute of technology, Tallaght, Ireland Last edited by kevinmccartin; July 9, 2015 at 20:35. Reason: no attachments 

July 9, 2015, 20:42 

#4 
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Glenn Horrocks
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In CFXPre go file export CCL.
When the free surface rapidly changes like this it is usually because the free surface you have specified is incompatible with the flow conditions (velocity or fluid motion or whatever) and this causes the fluid motion to rapidly drop. The problem is usually a incorrectly defined boundary condition. 

July 9, 2015, 20:49 
Attachments

#5 
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kevin
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Ghorrocks,
attached are 2 pictures. I am unable to find the .ccl file in the directory at the moment im not too sure how to access it from workbench. Thanks. Regards, Kevin 

July 9, 2015, 21:01 

#6 
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kevin
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Apolagies only saw your last message there. I tried to export but I keep getting a warning message saying "nothing to export" in the cfx pre. It is probably because I am using a virtual machine to access ANSYS.
Thanks Kevin 

July 9, 2015, 21:03 

#7 
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Glenn Horrocks
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CFXPre is the setup block in workbench. You can only access the CCL via the GUI from CFXPre.
Your images confirm what I suspected, you almost certainly have not specified the inlet BC correctly. The CCL will contain the information about what you have done. 

July 9, 2015, 21:09 

#8 
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kevin
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CCL file
# State file created: 2015/07/10 02:03:48 # CFX15.0.7 build 2014.04.2423.02131781 LIBRARY: CEL: EXPRESSIONS: DenH = (DenWater  DenRef ) DenRef = 1.185 [kg m^3] DenWater = 997 [kg m^3] DownH = 0.08[m] DownPres = DenH*g*DownVFWater*(DownHy) DownVFAir = step((yDownH)/1[m]) DownVFWater = 1DownVFAir UpH = 0.08[m] UpPres = DenH*g*UpVFWater*(UpHy) UpVFAir = step((yUpH)/1[m]) UpVFWater = 1UpVFAir END END MATERIAL GROUP: Air Data Group Description = Ideal gas and constant property air. Constant \ properties are for dry air at STP (0 C, 1 atm) and 25 C, 1 atm. END MATERIAL GROUP: CHT Solids Group Description = Pure solid substances that can be used for conjugate \ heat transfer. END MATERIAL GROUP: Calorically Perfect Ideal Gases Group Description = Ideal gases with constant specific heat capacity. \ Specific heat is evaluated at STP. END MATERIAL GROUP: Constant Property Gases Group Description = Gaseous substances with constant properties. \ Properties are calculated at STP (0C and 1 atm). Can be combined with \ NASA SP273 materials for combustion modelling. END MATERIAL GROUP: Constant Property Liquids Group Description = Liquid substances with constant properties. END MATERIAL GROUP: Dry Peng Robinson Group Description = Materials with properties specified using the built \ in Peng Robinson equation of state. Suitable for dry real gas modelling. END MATERIAL GROUP: Dry Redlich Kwong Group Description = Materials with properties specified using the built \ in Redlich Kwong equation of state. Suitable for dry real gas modelling. END MATERIAL GROUP: Dry Soave Redlich Kwong Group Description = Materials with properties specified using the built \ in Soave Redlich Kwong equation of state. Suitable for dry real gas \ modelling. END MATERIAL GROUP: Dry Steam Group Description = Materials with properties specified using the IAPWS \ equation of state. Suitable for dry steam modelling. END MATERIAL GROUP: Gas Phase Combustion Group Description = Ideal gas materials which can be use for gas phase \ combustion. Ideal gas specific heat coefficients are specified using \ the NASA SP273 format. END MATERIAL GROUP: IAPWS IF97 Group Description = Liquid, vapour and binary mixture materials which use \ the IAPWS IF97 equation of state. Materials are suitable for \ compressible liquids, phase change calculations and dry steam flows. END MATERIAL GROUP: Interphase Mass Transfer Group Description = Materials with reference properties suitable for \ performing either Eulerian or Lagrangian multiphase mass transfer \ problems. Examples include cavitation, evaporation or condensation. END MATERIAL GROUP: Liquid Phase Combustion Group Description = Liquid and homogenous binary mixture materials which \ can be included with Gas Phase Combustion materials if combustion \ modelling also requires phase change (eg: evaporation) for certain \ components. END MATERIAL GROUP: Particle Solids Group Description = Pure solid substances that can be used for particle \ tracking END MATERIAL GROUP: Peng Robinson Dry Hydrocarbons Group Description = Common hydrocarbons which use the Peng Robinson \ equation of state. Suitable for dry real gas models. END MATERIAL GROUP: Peng Robinson Dry Refrigerants Group Description = Common refrigerants which use the Peng Robinson \ equation of state. Suitable for dry real gas models. END MATERIAL GROUP: Peng Robinson Dry Steam Group Description = Water materials which use the Peng Robinson equation \ of state. Suitable for dry steam modelling. END MATERIAL GROUP: Peng Robinson Wet Hydrocarbons Group Description = Common hydrocarbons which use the Peng Robinson \ equation of state. Suitable for condensing real gas models. END MATERIAL GROUP: Peng Robinson Wet Refrigerants Group Description = Common refrigerants which use the Peng Robinson \ equation of state. Suitable for condensing real gas models. END MATERIAL GROUP: Peng Robinson Wet Steam Group Description = Water materials which use the Peng Robinson equation \ of state. Suitable for condensing steam modelling. END MATERIAL GROUP: Real Gas Combustion Group Description = Real gas materials which can be use for gas phase \ combustion. Ideal gas specific heat coefficients are specified using \ the NASA SP273 format. END MATERIAL GROUP: Redlich Kwong Dry Hydrocarbons Group Description = Common hydrocarbons which use the Redlich Kwong \ equation of state. Suitable for dry real gas models. END MATERIAL GROUP: Redlich Kwong Dry Refrigerants Group Description = Common refrigerants which use the Redlich Kwong \ equation of state. Suitable for dry real gas models. END MATERIAL GROUP: Redlich Kwong Dry Steam Group Description = Water materials which use the Redlich Kwong equation \ of state. Suitable for dry steam modelling. END MATERIAL GROUP: Redlich Kwong Wet Hydrocarbons Group Description = Common hydrocarbons which use the Redlich Kwong \ equation of state. Suitable for condensing real gas models. END MATERIAL GROUP: Redlich Kwong Wet Refrigerants Group Description = Common refrigerants which use the Redlich Kwong \ equation of state. Suitable for condensing real gas models. END MATERIAL GROUP: Redlich Kwong Wet Steam Group Description = Water materials which use the Redlich Kwong equation \ of state. Suitable for condensing steam modelling. END MATERIAL GROUP: Soave Redlich Kwong Dry Hydrocarbons Group Description = Common hydrocarbons which use the Soave Redlich Kwong \ equation of state. Suitable for dry real gas models. END MATERIAL GROUP: Soave Redlich Kwong Dry Refrigerants Group Description = Common refrigerants which use the Soave Redlich Kwong \ equation of state. Suitable for dry real gas models. END MATERIAL GROUP: Soave Redlich Kwong Dry Steam Group Description = Water materials which use the Soave Redlich Kwong \ equation of state. Suitable for dry steam modelling. END MATERIAL GROUP: Soave Redlich Kwong Wet Hydrocarbons Group Description = Common hydrocarbons which use the Soave Redlich Kwong \ equation of state. Suitable for condensing real gas models. END MATERIAL GROUP: Soave Redlich Kwong Wet Refrigerants Group Description = Common refrigerants which use the Soave Redlich Kwong \ equation of state. Suitable for condensing real gas models. END MATERIAL GROUP: Soave Redlich Kwong Wet Steam Group Description = Water materials which use the Soave Redlich Kwong \ equation of state. Suitable for condensing steam modelling. END MATERIAL GROUP: Soot Group Description = Solid substances that can be used when performing \ soot modelling END MATERIAL GROUP: User Group Description = Materials that are defined by the user END MATERIAL GROUP: Water Data Group Description = Liquid and vapour water materials with constant \ properties. Can be combined with NASA SP273 materials for combustion \ modelling. END MATERIAL GROUP: Wet Peng Robinson Group Description = Materials with properties specified using the built \ in Peng Robinson equation of state. Suitable for wet real gas modelling. END MATERIAL GROUP: Wet Redlich Kwong Group Description = Materials with properties specified using the built \ in Redlich Kwong equation of state. Suitable for wet real gas modelling. END MATERIAL GROUP: Wet Soave Redlich Kwong Group Description = Materials with properties specified using the built \ in Soave Redlich Kwong equation of state. Suitable for wet real gas \ modelling. END MATERIAL GROUP: Wet Steam Group Description = Materials with properties specified using the IAPWS \ equation of state. Suitable for wet steam modelling. END MATERIAL: Air Ideal Gas Material Description = Air Ideal Gas (constant Cp) Material Group = Air Data, Calorically Perfect Ideal Gases Option = Pure Substance Thermodynamic State = Gas PROPERTIES: Option = General Material EQUATION OF STATE: Molar Mass = 28.96 [kg kmol^1] Option = Ideal Gas END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 1.0044E+03 [J kg^1 K^1] Specific Heat Type = Constant Pressure END REFERENCE STATE: Option = Specified Point Reference Pressure = 1 [atm] Reference Specific Enthalpy = 0. [J/kg] Reference Specific Entropy = 0. [J/kg/K] Reference Temperature = 25 [C] END DYNAMIC VISCOSITY: Dynamic Viscosity = 1.831E05 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 2.61E2 [W m^1 K^1] END ABSORPTION COEFFICIENT: Absorption Coefficient = 0.01 [m^1] Option = Value END SCATTERING COEFFICIENT: Option = Value Scattering Coefficient = 0.0 [m^1] END REFRACTIVE INDEX: Option = Value Refractive Index = 1.0 [m m^1] END 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 EQUATION OF STATE: Density = 1.185 [kg m^3] Molar Mass = 28.96 [kg kmol^1] Option = Value END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 1.0044E+03 [J kg^1 K^1] Specific Heat Type = Constant Pressure END REFERENCE STATE: Option = Specified Point Reference Pressure = 1 [atm] Reference Specific Enthalpy = 0. [J/kg] Reference Specific Entropy = 0. [J/kg/K] Reference Temperature = 25 [C] END DYNAMIC VISCOSITY: Dynamic Viscosity = 1.831E05 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 2.61E02 [W m^1 K^1] END ABSORPTION COEFFICIENT: Absorption Coefficient = 0.01 [m^1] Option = Value END SCATTERING COEFFICIENT: Option = Value Scattering Coefficient = 0.0 [m^1] END REFRACTIVE INDEX: Option = Value Refractive Index = 1.0 [m m^1] END THERMAL EXPANSIVITY: Option = Value Thermal Expansivity = 0.003356 [K^1] END END END MATERIAL: Aluminium Material Group = CHT Solids, Particle Solids Option = Pure Substance Thermodynamic State = Solid PROPERTIES: Option = General Material EQUATION OF STATE: Density = 2702 [kg m^3] Molar Mass = 26.98 [kg kmol^1] Option = Value END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 9.03E+02 [J kg^1 K^1] END REFERENCE STATE: Option = Specified Point Reference Specific Enthalpy = 0 [J/kg] Reference Specific Entropy = 0 [J/kg/K] Reference Temperature = 25 [C] END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 237 [W m^1 K^1] END END END MATERIAL: Copper Material Group = CHT Solids, Particle Solids Option = Pure Substance Thermodynamic State = Solid PROPERTIES: Option = General Material EQUATION OF STATE: Density = 8933 [kg m^3] Molar Mass = 63.55 [kg kmol^1] Option = Value END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 3.85E+02 [J kg^1 K^1] END REFERENCE STATE: Option = Specified Point Reference Specific Enthalpy = 0 [J/kg] Reference Specific Entropy = 0 [J/kg/K] Reference Temperature = 25 [C] END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 401.0 [W m^1 K^1] END END END MATERIAL: Soot Material Group = Soot Option = Pure Substance Thermodynamic State = Solid PROPERTIES: Option = General Material EQUATION OF STATE: Density = 2000 [kg m^3] Molar Mass = 12 [kg kmol^1] Option = Value END REFERENCE STATE: Option = Automatic END ABSORPTION COEFFICIENT: Absorption Coefficient = 0 [m^1] Option = Value END END END MATERIAL: Steel Material Group = CHT Solids, Particle Solids Option = Pure Substance Thermodynamic State = Solid PROPERTIES: Option = General Material EQUATION OF STATE: Density = 7854 [kg m^3] Molar Mass = 55.85 [kg kmol^1] Option = Value END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 4.34E+02 [J kg^1 K^1] END REFERENCE STATE: Option = Specified Point Reference Specific Enthalpy = 0 [J/kg] Reference Specific Entropy = 0 [J/kg/K] Reference Temperature = 25 [C] END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 60.5 [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 EQUATION OF STATE: Density = 997.0 [kg m^3] Molar Mass = 18.02 [kg kmol^1] Option = Value END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 4181.7 [J kg^1 K^1] Specific Heat Type = Constant Pressure END REFERENCE STATE: Option = Specified Point Reference Pressure = 1 [atm] Reference Specific Enthalpy = 0.0 [J/kg] Reference Specific Entropy = 0.0 [J/kg/K] Reference Temperature = 25 [C] END DYNAMIC VISCOSITY: Dynamic Viscosity = 8.899E4 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 0.6069 [W m^1 K^1] END ABSORPTION COEFFICIENT: Absorption Coefficient = 1.0 [m^1] Option = Value END SCATTERING COEFFICIENT: Option = Value Scattering Coefficient = 0.0 [m^1] END REFRACTIVE INDEX: Option = Value Refractive Index = 1.0 [m m^1] END THERMAL EXPANSIVITY: Option = Value Thermal Expansivity = 2.57E04 [K^1] END END END MATERIAL: Water Ideal Gas Material Description = Water Vapour Ideal Gas (100 C and 1 atm) Material Group = Calorically Perfect Ideal Gases, Water Data Option = Pure Substance Thermodynamic State = Gas PROPERTIES: Option = General Material EQUATION OF STATE: Molar Mass = 18.02 [kg kmol^1] Option = Ideal Gas END SPECIFIC HEAT CAPACITY: Option = Value Specific Heat Capacity = 2080.1 [J kg^1 K^1] Specific Heat Type = Constant Pressure END REFERENCE STATE: Option = Specified Point Reference Pressure = 1.014 [bar] Reference Specific Enthalpy = 0. [J/kg] Reference Specific Entropy = 0. [J/kg/K] Reference Temperature = 100 [C] END DYNAMIC VISCOSITY: Dynamic Viscosity = 9.4E06 [kg m^1 s^1] Option = Value END THERMAL CONDUCTIVITY: Option = Value Thermal Conductivity = 193E04 [W m^1 K^1] END ABSORPTION COEFFICIENT: Absorption Coefficient = 1.0 [m^1] Option = Value END SCATTERING COEFFICIENT: Option = Value Scattering Coefficient = 0.0 [m^1] END REFRACTIVE INDEX: Option = Value Refractive Index = 1.0 [m m^1] END END END END FLOW: Flow Analysis 1 SOLUTION UNITS: Angle Units = [rad] Length Units = [m] Mass Units = [kg] Solid Angle Units = [sr] Temperature Units = [K] Time Units = [s] END ANALYSIS TYPE: Option = Steady State EXTERNAL SOLVER COUPLING: Option = None END END DOMAIN: Default Domain Coord Frame = Coord 0 Domain Type = Fluid Location = B22 BOUNDARY: Default Domain Default Boundary Type = WALL Location = F28.22 BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: back Boundary Type = SYMMETRY Location = back END BOUNDARY: bottom Boundary Type = WALL Location = bottom BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: cylinder Boundary Type = WALL Location = cylinderhalf BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: cylinder2 Boundary Type = WALL Location = cylinderhalf2 BOUNDARY CONDITIONS: MASS AND MOMENTUM: Option = No Slip Wall END WALL ROUGHNESS: Option = Smooth Wall END END END BOUNDARY: front Boundary Type = SYMMETRY Location = front END BOUNDARY: inlet Boundary Type = INLET Location = inlet BOUNDARY CONDITIONS: FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Normal Speed = 0.21 [m s^1] Option = Normal Speed END TURBULENCE: Eddy Length Scale = UpH Fractional Intensity = 0.05 Option = Intensity and Length Scale END END FLUID: air BOUNDARY CONDITIONS: VOLUME FRACTION: Option = Value Volume Fraction = UpVFAir END END END FLUID: water BOUNDARY CONDITIONS: VOLUME FRACTION: Option = Value Volume Fraction = UpVFWater END END END END BOUNDARY: outlet Boundary Type = OUTLET Location = outlet BOUNDARY CONDITIONS: FLOW REGIME: Option = Subsonic END MASS AND MOMENTUM: Option = Static Pressure Relative Pressure = 0 [Pa] END END END DOMAIN MODELS: BUOYANCY MODEL: Buoyancy Reference Density = DenRef Gravity X Component = 0 [m s^2] Gravity Y Component = g Gravity Z Component = 0 [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 DEFINITION: air Material = Air at 25 C Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID DEFINITION: water Material = Water Option = Material Library MORPHOLOGY: Option = Continuous Fluid END END FLUID MODELS: COMBUSTION MODEL: Option = None END FLUID: air FLUID BUOYANCY MODEL: Option = Density Difference END END FLUID: water FLUID BUOYANCY MODEL: Option = Density Difference END END HEAT TRANSFER MODEL: Fluid Temperature = 25 [C] Homogeneous Model = True Option = Isothermal END THERMAL RADIATION MODEL: Option = None END TURBULENCE MODEL: Option = k epsilon BUOYANCY TURBULENCE: Option = None END END TURBULENT WALL FUNCTIONS: Option = Scalable END END FLUID PAIR: air  water INTERPHASE TRANSFER MODEL: Option = None END MASS TRANSFER: Option = None END SURFACE TENSION MODEL: Option = None END END MULTIPHASE MODELS: Homogeneous Model = On FREE SURFACE MODEL: Option = Standard END END END INITIALISATION: Option = Automatic FLUID: air INITIAL CONDITIONS: VOLUME FRACTION: Option = Automatic with Value Volume Fraction = UpVFAir END END END FLUID: water INITIAL CONDITIONS: VOLUME FRACTION: Option = Automatic with Value Volume Fraction = UpVFWater END END END INITIAL CONDITIONS: Velocity Type = Cartesian CARTESIAN VELOCITY COMPONENTS: Option = Automatic with Value U = 0.21 [m s^1] V = 0 [m s^1] W = 0 [m s^1] END STATIC PRESSURE: Option = Automatic with Value Relative Pressure = UpPres END TURBULENCE INITIAL CONDITIONS: Option = Medium Intensity and Eddy Viscosity Ratio END END END MESH ADAPTION: Activate Adaption = On Domain Name = Default Domain Save Intermediate Files = Off Subdomain List = B22 ADAPTION ADVANCED OPTIONS: Node Allocation Parameter = 1.6 Number of Adaption Levels = 2 END ADAPTION CONVERGENCE CRITERIA: Adaption Target Residual = 0.001 Maximum Iterations per Step = 100 Option = RMS Norm for Residuals END ADAPTION CRITERIA: Maximum Number of Adaption Steps = 2 Node Factor = 4 Option = Multiple of Initial Mesh Variables List = air.Volume Fraction END ADAPTION METHOD: Minimum Edge Length = 0.0 Option = Solution Variation END END OUTPUT CONTROL: RESULTS: File Compression Level = Default Option = Standard END END SOLVER CONTROL: Turbulence Numerics = First Order ADVECTION SCHEME: Option = High Resolution END CONVERGENCE CONTROL: Length Scale Option = Conservative Maximum Number of Iterations = 100 Minimum Number of Iterations = 1 Timescale Control = Auto Timescale Timescale Factor = 1.0 END CONVERGENCE CRITERIA: Residual Target = 1.E4 Residual Type = RMS END DYNAMIC MODEL CONTROL: Global Dynamic Model Control = On END END END COMMAND FILE: Version = 15.0 END 

July 9, 2015, 21:11 

#9 
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kevin
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Ghorrocks,
Above is the CCL file. I am not sure how to set boundaries any other way. Set an inlet velocity and an outlet static pressure. I used the 2 walls as non slip walls along with cylinder surfaces. The top was used as an opening with entrainment. Thanks Kevin 

July 9, 2015, 21:22 

#10 
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Glenn Horrocks
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The boundaries you have defined are inconsistent. You have set a flow rate and free surface height at the inlet (which is it applying), but the exit boundary condition requires the free surface to be much lower than you specify and this lower height propagates back up the domain.
You need to be a bit more clever with your exit boundary. I would consider replacing the exit boundary with a chamber where you keep the free surface height at the desired level. Or you might use a momentum source term to do it. Whatever you do, have a careful think about exactly what your BCs are specifying. The way this tutorial sets up the boundary conditions might not be the best way for you to do it in your case. 

July 9, 2015, 21:36 

#11 
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kevin
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Ghorrocks,
Thanks for your time and recommendations. I will do some additional research on this tomorrow and see how I do. Thanks for your time, you sir are a gent. Regards Kevin 

October 13, 2022, 18:01 

#12  
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Ashkan Kashani
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I understand it's been quite a while since this discussion was made but I was hoping to see your comment on my problem here as it's relevant.
Quote:
I'm not sure exactly what you meant by a "chamber" but I set a part of the outlet, as high as the water surface elevation at the inlet, as a noslip wall in order to force the water surface to rise. However, by doing so, longlasting unsteadiness appears in the form of travelling waves along the channel length. I'm thinking of artificially increasing the viscosity close to the domain boundaries in the hope of accelerating the attenuation of these waves. However, I'm not sure if this trick is physically/numerically appropriate. 

October 13, 2022, 21:43 

#13 
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Glenn Horrocks
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The chamber I was referring to is to artificially put a chamber on the exit boundary, designed to keep the water level at the correct level. You could do this with a weir arrangement.
Transient waves in free surface simulations are normal. I do not generally recommend applying nonphysical effects to remove them  they are real, so you should model them. You probably have to use a transient model anyway, so modelling the waves should not be too much of a problem.
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coefficient drag, cylinder, free surface, surface piercing 
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