Materials, Cell Zones and Rotating Reference Frames
Material properties and equations of state define how pressure, temperature, density, enthalpy, viscosity and conductivity are related. Cell-zone controls assign those materials to the mesh and optionally add rotating-reference-frame motion.
Theory reference. Each option entry includes a link to the corresponding equation, physical model, closure, or numerical method in the Theory Manual. Defaults, availability, simulation effects, and practical guidance are documented directly with the GUI option.
Material management
Material controls define the property data available to zones and VOF phases.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Material Library / User Defined LibDefault: Material Library | Selects between the supplied material collection and the user-created material collection shown in the material tree. | InitializationReporting / display This selector changes which property definitions are available for assignment; it does not change the case until a material is selected/edited/applied. | Use the supplied library for standard entries and the user-defined library for validated custom materials. | Material/property formulation |
| Material Search | Filters/highlights entries in the material tree. | Reporting / display No simulation effect. | Use it only to locate a material; the case changes only when the material is assigned/applied. | Material/property formulation |
| Material Type: Fluid | Creates/edits a carrier-fluid material with EOS, caloric and transport properties. | Physics Determines compressibility regime, density, sound speed, enthalpy and viscous/thermal transport. | Define all properties over the full expected temperature/pressure range. | Material/property formulation |
| Material Type: Solid | Creates/edits a solid thermal material with density, heat capacity and conductivity. | Physics Determines solid thermal inertia and heat conduction in CHT/solid-energy zones. | Use measured temperature-dependent data for wide thermal ranges. | Material/property formulation |
| Material Type: Particle | Creates/edits dispersed-particle/droplet material properties. | Physics Affects drag/thermal response, particle inertia, IATE/breakup/coalescence scales. | Use properties consistent with the dispersed model and expected phase state. | Material/property formulation |
| Add / New / Remove material | Creates, adds or removes material entries in the user/material libraries shown by the GUI. | Initialization Changes available case definitions; removing an assigned material can invalidate a zone setup. | Create materials before assigning zones/phases and avoid deleting materials in use. | Material/property formulation |
| Apply Changes | Commits edited material properties. | InitializationPhysics Subsequent thermodynamic/transport calculations use the new data. | After changing a material in an existing case, re-check initialization and convergence. | Material/property formulation |
Fluid equation of state and basic properties
The selected EOS automatically determines whether CMPS uses compressible or constant-density carrier behavior.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| EOS: Ideal Gas | Uses gas density from the ideal-gas relation, approximately \(\rho=p/(RT)\), with caloric properties supplied by the material model. | PhysicsAccuracy Density responds to pressure and temperature; enables compressible carrier behavior. | Use for gases in ranges where ideal-gas behavior is adequate. | Ideal-gas EOS |
| Molecular Weight | Sets mixture/material gas constant through \(R=R_u/M\) for ideal-gas use. | PhysicsAccuracy Directly changes density, sound/thermal scales and mixture thermodynamics. | Use consistent units (GUI uses g/mol) and composition basis. | Thermodynamic state |
| EOS: Stiffened Gas | Uses a pressure-shifted compressible closure with thermodynamic pressure based on \(p+p_\infty\). | PhysicsAccuracy Represents liquids/dense fluids with finite compressibility more realistically than ideal gas/constant density. | Use only with calibrated \(\gamma\), \(p_\infty\), heat capacity and reference data. | Stiffened-gas EOS |
| Specific Heat Ratio γ | Stiffened-gas caloric/acoustic parameter. | PhysicsAccuracy Changes compressibility, sound speed and energy-pressure coupling. | Must be greater than one and consistent with the selected stiffened-fluid model. | Caloric model |
| Stiffened Pressure p∞ | Pressure shift in the stiffened-gas EOS. | PhysicsAccuracy Strongly controls liquid compressibility and acoustic speed. | Use fluid-specific calibrated values; do not infer from operating pressure. | Stiffened-gas EOS |
| EOS: Incompressible / Constant Density | Uses a prescribed density rather than pressure-dependent density; pressure is obtained through artificial compressibility/coupling. | PhysicsAccuracy Removes physical acoustic compressibility and makes density independent of pressure. | Use for effectively constant-density liquids/flows where compressibility is negligible. | Constant-density closure |
| Density | For constant-density fluids/solids/particles, sets mass per unit volume. | PhysicsAccuracy Controls inertia, mass flow, Reynolds number, buoyancy/source response and thermal inertia where relevant. | Use operating-temperature density consistent with the model. | Constant-density closure |
| Specific Heat Cp | Defines sensible enthalpy/energy variation; for simple caloric behavior \(dh\approx C_p dT\). | PhysicsAccuracy Controls thermal inertia and temperature change for a given heat input. | Use temperature-dependent data when the range is wide. | Caloric model |
| Thermal Conductivity k | Defines Fourier heat conduction \(\mathbf q=-k\nabla T\) for isotropic media. | PhysicsAccuracy Higher conductivity smooths temperature gradients and increases conductive heat transfer. | Use appropriate phase/material data and temperature dependence. | Thermal conductivity |
| Dynamic Viscosity μ | Defines molecular viscous stress scale; Reynolds number varies inversely with \(\mu\). | PhysicsAccuracy Changes boundary-layer thickness, shear, pressure loss, heat transfer and turbulence scales. | Use correct temperature dependence for gas/high-temperature flow. | Dynamic viscosity |
Temperature-dependent property methods
The property-method selector appears only for properties that support the selected method.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Property Method: Constant | Uses one value over the entire temperature range. | PhysicsAccuracy Fast and robust but can be inaccurate when properties vary strongly with temperature. | Use for narrow temperature ranges or genuinely constant properties. | Property methods and admissibility |
| Property Method: Piecewise Polynomial | Uses one or more temperature ranges with polynomial coefficients, conceptually \(f(T)=\sum_m a_mT^m\). | PhysicsAccuracy Captures nonlinear temperature dependence; out-of-range/poor coefficients can strongly affect stability and accuracy. | Cover the entire expected temperature range and verify continuity/range ordering. | Property methods and admissibility |
| Number of temperature ranges | Sets how many polynomial ranges are entered. | Accuracy More ranges allow better fits but increase data-entry complexity and risk of gaps/discontinuities. | Use the minimum number needed to fit validated data. | Property methods and admissibility |
| Polynomial coefficients / temperature range boundaries | Defines coefficients and interval limits for each piecewise polynomial. | PhysicsAccuracy Directly controls the computed material property. | Check units and evaluate the curve at representative temperatures before solving. | Property methods and admissibility |
| Property Method: Kinetic Theory | Uses the kinetic-theory property relation where enabled for the selected property/material. | PhysicsAccuracy Makes transport/property response depend on molecular/thermodynamic quantities rather than a fixed fit. | Use only when the required molecular inputs and validity range are appropriate. | Property methods and admissibility |
| High-temperature coefficient correlation | Uses the GUI high-temperature coefficient correlation available for conductivity or viscosity over its stated high-temperature range. | PhysicsAccuracy Can represent high-temperature gas transport where simple low-temperature laws fail. | Use only inside the published/entered valid range and with consistent species/material coefficients. | Property methods and admissibility |
| Sutherland’s Law | For gas viscosity, \(\mu(T)=\mu_0(T/T_0)^{3/2}(T_0+S)/(T+S)\). | PhysicsAccuracy Viscosity rises with temperature in the characteristic gas-law form, affecting Reynolds number and wall shear/heat transfer. | Use for gases in the temperature range where Sutherland parameters are valid. | Viscosity laws |
| Sutherland μ0 | Reference dynamic viscosity in the Sutherland relation. | PhysicsAccuracy Sets the absolute viscosity level and therefore Reynolds number, wall shear and viscous heating. | Use the value paired with the selected reference temperature and Sutherland constant. | Viscosity laws |
| Sutherland T0 | Reference temperature associated with μ0 in the Sutherland relation. | PhysicsAccuracy Shifts/scales the temperature dependence of viscosity. | Use the same parameter set as μ0 and S. | Viscosity laws |
| Sutherland S | Sutherland temperature constant in \(\mu=\mu_0(T/T_0)^{3/2}(T_0+S)/(T+S)\). | PhysicsAccuracy Controls the curvature of the viscosity-versus-temperature relation and therefore high/low-temperature viscous behavior. | Use a calibrated value for the selected gas and temperature range. | Viscosity laws |
| Anisotropic Thermal ConductivityDefault: Off unless selected | For solids, uses a conductivity tensor \(\mathbf q=-\mathbf K\nabla T\) instead of a scalar. | PhysicsAccuracy Heat flows preferentially along directions with larger tensor conductivity. | Use for composites/crystals/laminates where conductivity is direction dependent; ensure tensor axes match mesh/global coordinates. | Conductivity laws |
| Conductivity tensor components | Entries define \(\mathbf K\). | PhysicsAccuracyStability / convergence Changing off-diagonal/diagonal terms changes direction and magnitude of heat flow. | Use a physically symmetric positive-definite tensor unless the material model specifically requires otherwise. | Conductivity laws |
Particle and species material properties
These properties become active when dispersed phase or species transport is enabled.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Particle Density | Particle/droplet material density. | PhysicsAccuracy Controls particle inertia, relaxation time, slip response and mass loading. | Use actual phase density at the relevant conditions. | Dispersed material properties |
| Particle Specific Heat | Particle thermal capacity. | PhysicsAccuracy Controls particle temperature response to convective heat transfer. | Use temperature dependence if heating/cooling range is wide. | Dispersed material properties |
| Particle Diameter | Characteristic diameter used when a fixed/material diameter is required. | PhysicsAccuracy Drag and heat-transfer time scales depend strongly on diameter; surface area per mass also changes. | Use the representative size or IATE-consistent initial size. | Dispersed material properties |
| Surface Tension | Interfacial surface tension for droplet/breakup/coalescence closures. | PhysicsAccuracy Changes Weber/Eötvös-type breakup thresholds and interfacial response. | Use phase-pair data at the relevant temperature/composition. | Dispersed material properties |
| Species Molecular Weight | Defines each species molar mass. | PhysicsAccuracy Controls mixture molecular weight, gas constant, diffusion/thermodynamic quantities. | Use consistent species data. | Species thermochemical properties |
| Species Heat Capacity | Temperature-dependent species caloric property. | PhysicsAccuracy Controls mixture Cp, enthalpy and reacting temperature. | Use data consistent with the thermodynamic mechanism. | Species thermochemical properties |
| Species Enthalpy | Species enthalpy/reference thermochemistry data. | PhysicsAccuracy Controls reaction heat release and mixture energy. | Use consistent reference states for all species. | Species thermochemical properties |
Cell zones and rotating reference frames
Cell-zone settings map material/physics models onto mesh volumes.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Zone Type: Fluid | Assigns the selected cell zone to the fluid equation set. | Physics Activates carrier-flow equations and optional fluid physics in the zone. | Use only for flow-containing volume regions. | Zone/material coupling |
| Zone Type: Solid | Assigns the cell zone to solid energy conduction. | Physics Replaces fluid momentum/pressure equations with solid thermal behavior for the zone. | Use for solid regions participating in heat conduction/CHT. | Solid energy equation |
| Assigned Material | Selects the fluid or solid material used in the zone. | PhysicsInitialization Directly changes EOS, density, heat capacity and transport coefficients. | Verify material before initialization; changing material can require a fresh initial state. | Zone/material coupling |
| Assigned Particle Material | Selects the dispersed material associated with the fluid zone when particle equations are active. | PhysicsInitialization Changes particle density, Cp, diameter/surface properties and coupling. | Assign the intended dispersed phase material. | Zone/material coupling |
| Enable MRFDefault: Off | Activates a rotating-reference-frame/grid velocity for the cell zone. CMPS uses absolute flow variables with a grid/frame velocity \(\mathbf v_g=\boldsymbol\Omega\times(\mathbf r-\mathbf r_0)\) in relative convection. | Physics Changes convective fluxes and rotating-frame source/energy behavior without physically moving the mesh. | Use for steady rotating machinery approximations when an MRF model is appropriate. | Rotating-reference-frame kinematics |
| Rotation Axis X | X component of the MRF rotation-axis direction used to construct \(\boldsymbol\Omega\). | Physics Changes the direction of frame velocity and rotating-frame effects. | Enter the physical rotor-axis direction together with Y and Z components. | Rotating-reference-frame kinematics |
| Rotation Axis Y | Y component of the MRF rotation-axis direction. | Physics Changes the orientation of the rotating reference frame. | Use coordinates consistent with the mesh. | Rotating-reference-frame kinematics |
| Rotation Axis Z | Z component of the MRF rotation-axis direction. | Physics Changes the orientation of the rotating reference frame. | For a planar 2D rotating case this is typically the out-of-plane axis; verify the actual geometry. | Rotating-reference-frame kinematics |
| Center of Rotation X | X coordinate of \(\mathbf r_0\) in \(\mathbf v_g=\boldsymbol\Omega\times(\mathbf r-\mathbf r_0)\). | Physics Moves the rotation axis location and changes frame velocity throughout the zone. | Use the physical rotor-axis center in mesh coordinates. | Rotating-reference-frame kinematics |
| Center of Rotation Y | Y coordinate of the MRF rotation center. | Physics Moves the rotation axis and changes local frame velocity. | Use the physical rotor-axis center in mesh coordinates. | Rotating-reference-frame kinematics |
| Center of Rotation Z | Z coordinate of the MRF rotation center. | Physics Moves the rotation axis and changes local frame velocity. | Use the physical rotor-axis center in mesh coordinates. | Rotating-reference-frame kinematics |
| Angular Velocity [rad/s] | Magnitude/sign of rotational speed. | PhysicsAccuracy Directly scales frame velocity and rotational effects; sign sets rotation direction. | Convert RPM correctly: \(\Omega=2\pi\,RPM/60\). | Rotating-reference-frame kinematics |
| OK / Cancel | Commits or discards cell-zone edits. | Initialization OK changes the active case definition. | Review zone material and MRF values before committing. | Zone/material coupling |