# Simple piston movement in cylinder- fluid models

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 LinkBack Thread Tools Search this Thread Display Modes July 8, 2016, 01:08 Simple piston movement in cylinder- fluid models
#1
Member

Arun subramanian
Join Date: Jun 2016
Location: Florence,Italy
Posts: 46
Rep Power: 7 Dear friends ,

I am trying to just make a very simple piston movement analysis. My mesh is perfect ( just used sweep in mesh ) and I have setup transient conditions with sinusoidal motion of piston.

I am attaching my CCL with this.
1) I have a problem that there is (almost) no difference in pressure/ temperature with change in fluid model from none, thermal energy, isothermal , total energy. why does this happen and how can I avoid this problem? I need to see changes in pressure, temperature for each model .

2)When I try to use volume rendering to find how temperature changes, I get an error that minimum is greater than maximum. But when and where should I change something? I did some crude techniques to try myself but in vain. What is a good approach in viewing my results? [both in colors, animation and just numbers, plots ]

Also , are there equations to theoretically compare the results obtained from ANSYS for each model? Just a simple piston movement and I have been breaking my head for quite too long !

Cheers,
Arun

CCL :

# State file created: 2016/07/08 07:57:30
# Build 16.2 2015.06.30-00.06-134402

LIBRARY:
CEL:
EXPRESSIONS:
dt = 1.24972e-5[s]
greitis = 5000[rad s^-1]
gretis = -3.6[m/s]*t+Y0
poslinkis = greitis *t
poslinkis cilindro = -sin(poslinkis )*0.0042[m]
slegio kitimas p = slegio kitimas(t)
su funcijos duomenimis = Function 1(t)
END
END
ADDITIONAL VARIABLE: AV
Option = Definition
Tensor Type = SCALAR
Units = [Pa]
Variable Type = Specific
END
ADDITIONAL VARIABLE: Additional Variable 1
Option = Definition
Tensor Type = VECTOR
Units = [Pa]
Variable Type = Volumetric
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 = 1.831E-05 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 2.61E-2 [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 = 1.831E-05 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 2.61E-02 [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 = 8.899E-4 [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 = 2.57E-04 [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 = 9.4E-06 [kg m^-1 s^-1]
Option = Value
END
THERMAL CONDUCTIVITY:
Option = Value
Thermal Conductivity = 193E-04 [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 = Transient
EXTERNAL SOLVER COUPLING:
Option = None
END
INITIAL TIME:
Option = Automatic with Value
Time = 0 [s]
END
TIME DURATION:
Option = Total Time
Total Time = 0.01 [s]
END
TIME STEPS:
Option = Timesteps
Timesteps = 0.0001 [s]
END
END
DOMAIN: Default Domain
Coord Frame = Coord 0
Domain Type = Fluid
Location = B4
BOUNDARY: Boundary 1
Boundary Type = WALL
Location = F14.4
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
Wall Velocity Relative To = Mesh Motion
END
MESH MOTION:
Option = Specified Displacement
DISPLACEMENT:
Displacement X Component = 0 [m]
Displacement Y Component = 0 [m]
Displacement Z Component = poslinkis cilindro
Option = Cartesian Components
END
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
BOUNDARY: Boundary 2
Boundary Type = WALL
Location = F13.4
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
Wall Velocity Relative To = Mesh Motion
END
MESH MOTION:
Option = Stationary
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
BOUNDARY: Default Domain Default
Boundary Type = WALL
Location = F11.4,F12.4
BOUNDARY CONDITIONS:
HEAT TRANSFER:
Option = Adiabatic
END
MASS AND MOMENTUM:
Option = No Slip Wall
Wall Velocity Relative To = Mesh Motion
END
MESH MOTION:
Option = Unspecified
END
WALL ROUGHNESS:
Option = Smooth Wall
END
END
END
DOMAIN MODELS:
BUOYANCY MODEL:
Option = Non Buoyant
END
DOMAIN MOTION:
Option = Stationary
END
MESH DEFORMATION:
Displacement Relative To = Previous Mesh
Option = Regions of Motion Specified
MESH MOTION MODEL:
Option = Displacement Diffusion
MESH STIFFNESS:
Option = Increase near Small Volumes
Stiffness Model Exponent = 10
REFERENCE VOLUME:
Option = Value
Reference Volume = 1.0 [m^3]
END
END
END
END
REFERENCE PRESSURE:
Reference Pressure = 1 [atm]
END
END
FLUID DEFINITION: Fluid 1
Material = Air at 25 C
Option = Material Library
MORPHOLOGY:
Option = Continuous Fluid
END
END
FLUID MODELS:
COMBUSTION MODEL:
Option = None
END
HEAT TRANSFER MODEL:
Option = Thermal Energy
END
THERMAL RADIATION MODEL:
Option = None
END
TURBULENCE MODEL:
Option = SST
END
TURBULENT WALL FUNCTIONS:
Option = Automatic
END
END
INITIALISATION:
Option = Automatic
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 = 1 [MPa]
END
TEMPERATURE:
Option = Automatic with Value
Temperature = 100 [K]
END
TURBULENCE INITIAL CONDITIONS:
Option = Medium Intensity and Eddy Viscosity Ratio
END
END
END
END
OUTPUT CONTROL:
MONITOR OBJECTS:
MONITOR BALANCES:
Option = Full
END
MONITOR FORCES:
Option = Full
END
MONITOR PARTICLES:
Option = Full
END
MONITOR POINT: Monitor Point 1
Cartesian Coordinates = 0.0032344 [m], 0.000666392 [m], -0.0025 [m]
Coord Frame = Coord 0
Option = Cartesian Coordinates
Output Variables List = Temperature,Absolute Pressure,Mesh \
Displacement,Total Pressure,Velocity,Pressure,Total Temperature
MONITOR LOCATION CONTROL:
Domain Name = Default Domain
Interpolation Type = Nearest Vertex
END
POSITION UPDATE FREQUENCY:
Option = Every Timestep
END
END
MONITOR POINT: Monitor Point 2
Cartesian Coordinates = -0.000500914 [m], -0.00187798 [m], 0.025 [m]
Coord Frame = Coord 0
Option = Cartesian Coordinates
Output Variables List = Mesh Displacement,Pressure,Total \
Temperature,Absolute Pressure,Temperature,Total Mesh Displacement
MONITOR LOCATION CONTROL:
Interpolation Type = Nearest Vertex
END
POSITION UPDATE FREQUENCY:
Option = Every Timestep
END
END
MONITOR RESIDUALS:
Option = Full
END
MONITOR TOTALS:
Option = Full
END
END
RESULTS:
Extra Output Variables List = Total Mesh Displacement X,Total Mesh \
Displacement Z,Total Mesh Displacement Y,Absolute Pressure,Total Mesh \
Displacement,Total Pressure
File Compression Level = Default
Option = Standard
Output Equation Residuals = All
END
TRANSIENT RESULTS: Transient Results 1
Extra Output Variables List = Total Pressure,Total Mesh Displacement \
X,Total Mesh Displacement Y,Total Mesh Displacement Z,Absolute Pressure
File Compression Level = Default
Option = Standard
OUTPUT FREQUENCY:
Option = Every Timestep
END
END
END
SOLVER CONTROL:
Turbulence Numerics = First Order
ADVECTION SCHEME:
Option = High Resolution
END
CONVERGENCE CONTROL:
Maximum Number of Coefficient Loops = 4
Minimum Number of Coefficient Loops = 1
Timescale Control = Coefficient Loops
END
CONVERGENCE CRITERIA:
Residual Target = 1.E-4
Residual Type = RMS
END
TRANSIENT SCHEME:
Option = Second Order Backward Euler
TIMESTEP INITIALISATION:
Option = Automatic
END
END
END
END
COMMAND FILE:
Version = 16.2
END
Attached Images Capture3..jpg (61.7 KB, 37 views) Capture1.jpg (73.0 KB, 31 views) Capture.jpg (63.7 KB, 25 views) 1 is.jpg (111.6 KB, 21 views) 1 is mesh.PNG (43.0 KB, 16 views)   July 8, 2016, 02:22 #2 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 16,722 Rep Power: 130    If you run this with none, thermal energy, isothermal options this model should crash. These are all incompressible fluids and you are compressing it so that does not work. The only option which should work is total energy as that is the only option which models a fully compressible fluid. You should be able to get this within a few percent of the analytical answer. I have done benchmarks on this years ago and got very accurate results so it can be done. I can see straight off: * Your time step is too big. Use adaptive time steps with 3-5 coeff loops per iteration. Then the solver will find the time step size for you. * Your convergence criteria needs checking. 1E-4 might be too loose. * You set a maximum coeff loops of 4. Remove this option. * You should do a mesh sensitivity study as well, but for simple piston compression of a gas this is not very important. It will only become important if the gas starts to flow somewhere.   July 8, 2016, 02:29 #3 Member   Arun subramanian Join Date: Jun 2016 Location: Florence,Italy Posts: 46 Rep Power: 7 Thank you very much. I will try this and get back.    July 8, 2016, 02:31 #4 Member   Arun subramanian Join Date: Jun 2016 Location: Florence,Italy Posts: 46 Rep Power: 7 These are all incompressible fluids and you are compressing it so that does not work. The only option which should work is total energy as that is the only option which models a fully compressible fluid. But Air at 25 degs is compressible gas automatically...no?   July 8, 2016, 02:54 #5 Super Moderator   Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 16,722 Rep Power: 130    Air at 25C just takes material properties at 25C and then defines an incompressible fluid.  Tags cfx, piston cylinder Thread Tools Search this Thread Show Printable Version Email this Page Search this Thread: Advanced Search Display Modes Linear Mode Switch to Hybrid Mode Switch to Threaded Mode Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are Off Pingbacks are On Refbacks are On Forum Rules Similar Threads Thread Thread Starter Forum Replies Last Post Sanyo CFX 17 August 15, 2015 06:20 Whitworth ANSYS 5 March 3, 2015 23:50 kshitij ANSYS 0 September 22, 2012 23:08 mosman Main CFD Forum 0 August 7, 2011 01:40 Abhi Main CFD Forum 12 July 8, 2002 09:11

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