Physics Models
The Physics panel selects the physical equations and closures that CMPS solves. These are among the most consequential GUI controls: they can change the governing equations, turbulence closure, thermodynamic regime, phase equations and wall treatment.
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.
Compressible / incompressible status is determined automatically. The current GUI displays the resulting regime from the material/EOS and VOF composition. It should not be treated as an independent physics switch.
Flow regime and carrier model
Select the model appropriate to the physical Reynolds/Mach regime and required fidelity.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Flow Regime: Compressible / IncompressibleDefault: Automatic | The regime follows the selected material equations of state. Ideal/stiffened-gas constituents use the compressible carrier formulation; constant-density material uses artificial-compressibility pressure coupling. In VOF, a compressible constituent makes the mixture compressible. | Physics Changes density-pressure coupling, acoustic characteristics and energy/thermodynamic behavior. | Select materials/EOS correctly; use the displayed regime as a check of the case definition. | Automatic flow-regime selection |
| Artificial speed / velocity ratioDefault: 5 | For constant-density flow, sets the velocity-proportional part of the artificial acoustic speed: \(c_{ac}=\max(U_{min},R_{ac}|\mathbf u|)\). | Stability / convergenceCost Larger \(R_{ac}\) strengthens pressure-velocity coupling but increases spectral stiffness and may reduce pseudo-time step. | Increase cautiously if pressure propagation is too weak; avoid unnecessarily large values. | Artificial-compressibility pressure equation |
| Minimum artificial speedDefault: 1 m/s | The floor \(U_{min}\) in \(c_{ac}=\max(U_{min},R_{ac}|\mathbf u|)\). | Stability / convergenceCost Prevents the artificial pressure wave speed from collapsing near stagnation/initially quiescent regions. Too large a floor makes the system stiffer. | Keep the floor modest relative to characteristic flow velocity. | Artificial-compressibility pressure equation |
| Inviscid | Solves carrier conservation without molecular viscous stresses/heat conduction. | PhysicsCost Removes boundary layers and viscous losses. Usually cheaper but unsuitable where skin friction or viscous heating matters. | Use for genuinely inviscid studies or preliminary external-flow estimates. | Carrier governing equations |
| Laminar | Includes molecular viscous stress and heat conduction without turbulence closure. | PhysicsAccuracyCost Resolves laminar boundary layers and viscous losses. | Use when Reynolds number/flow state supports laminar assumptions or for controlled laminar validation cases. | Carrier governing equations |
| GE-RANS | Adds two-equation generalized eddy-viscosity turbulence transport for \(k\) and \(\omega\), with turbulent viscosity and turbulent heat/species diffusion. | PhysicsCost Introduces turbulence transport, production/dissipation and additional stiffness/cost. | General default for statistically steady turbulent engineering flows. | GE k-ω transport equations |
| SAS | Extends GE-RANS with the scale-adaptive source \(Q_{SAS}\) in the \(\omega\) equation so resolved unsteadiness can be activated where grid/time resolution permits. | PhysicsAccuracyCost Can resolve more unsteady turbulent structures than steady RANS and therefore needs suitable mesh/time resolution and greater cost. | Use only for transient simulations intended to resolve unsteady turbulent content. | SAS source term |
| Viscous DissipationDefault: On | Includes conversion of mechanical work into internal energy through \(\Phi=\boldsymbol\tau:\nabla\mathbf u\). | PhysicsAccuracy Raises temperature where viscous work is important, especially high-speed/high-shear flows. | Keep enabled for compressible/high-speed/aerothermal cases. | Total-energy equation |
GE-RANS turbulence options
These controls modify the turbulence closure and therefore can affect separation, mixing, pressure loss and heat transfer.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Realizable GE-RANS Scale OptionDefault: On | Uses the realizability-aware turbulent time/viscosity scale in the GE-RANS closure rather than an unrestricted scale. | PhysicsStability / convergenceAccuracy Limits excessive turbulent viscosity in strong strain/rotation and generally improves robustness/physicality. | Keep enabled unless reproducing a specific comparison that requires the alternative scale. | Turbulent time scale and eddy viscosity |
| Low Reynolds Number ModificationDefault: Off | Activates low-Reynolds-number modifications of turbulence coefficients/near-wall behavior. | PhysicsAccuracy Makes turbulence closure sensitive to viscous Reynolds number and may improve low-y+ resolved-wall behavior; can also increase sensitivity to near-wall resolution. | Use with wall-resolved meshes and appropriate first-cell spacing. | Low-Re modification |
| Turbulent Production LimiterDefault: On | Bounds turbulence production so excessive local strain does not create unphysical \(k\) growth. | Stability / convergenceAccuracy Usually improves robustness in stagnation/strong-shear regions, but can reduce turbulence production if too restrictive. | Recommended for general RANS use. | Turbulence production |
| Kato-Launder LimiterDefault: Off | Uses a vorticity/strain-aware production treatment designed to reduce excessive production near stagnation points. | PhysicsAccuracy Can improve stagnation-region predictions and change separation/heat-transfer behavior. | Enable when stagnation-point overproduction is a known issue and compare against baseline. | Turbulence production |
| SSTm ModelDefault: Off | Selects the modified SST-related turbulence treatment available in CMPS, including the associated compressibility/dilatation handling. | PhysicsAccuracy Changes turbulent production/dissipation response in compressible regions. | Use when the intended turbulence calibration requires this variant; do not switch casually between calibrated variants. | Turbulent time scale and eddy viscosity |
| Curvature Correction: OffDefault: Off | No curvature/rotation correction is applied to turbulence production. | Physics Baseline turbulence response. | Use as reference unless strong streamline curvature/rotation is important. | Curvature corrections |
| Curvature Correction: Hellsten | Applies the Hellsten-style curvature/rotation correction to the turbulence closure. | PhysicsAccuracy Can change turbulent viscosity and separation in curved/rotating shear layers. | Use for flows where curvature/rotation materially affects turbulence; compare sensitivity. | Curvature corrections |
| Curvature Correction: Smirnov & Menter | Applies the alternative rotation/curvature correction exposed in the GUI. | PhysicsAccuracy Changes local turbulence production through strain/rotation invariants. | Use for validated use cases where curvature correction is required. | Curvature corrections |
| Cr1Default: 1 | First calibration constant of the curvature/rotation correction. It multiplies the principal correction response before final limiting. | PhysicsAccuracy Changing Cr1 changes how strongly curvature/rotation modifies turbulence production. | Keep the calibrated default unless carrying out a documented turbulence-model sensitivity study. | Curvature corrections |
| Cr2Default: 12 | Second curvature/rotation calibration constant controlling sensitivity of the correction to the local strain/rotation indicator. | PhysicsAccuracy Changing Cr2 can make the correction react more or less strongly to curved/rotating shear. | Keep the calibrated default for normal use. | Curvature corrections |
| Cr3Default: 1 | Third curvature/rotation calibration constant used in the correction response. | PhysicsAccuracy Changes the balance of the local curvature/rotation contribution and can alter separation and turbulent viscosity. | Keep the calibrated default unless validated data support a change. | Curvature corrections |
| CmaxDefault: 1.25 | Upper bound applied to the curvature/rotation correction factor. | PhysicsAccuracyStability / convergence A lower value limits model authority; a higher value permits stronger turbulence-production modification and can increase sensitivity. | Treat this as a model-calibration bound, not a convergence control. | Curvature corrections |
| Turbulent Prandtl NumberDefault: 0.85 | Controls turbulent thermal conductivity: \(k_t=\mu_t C_p/Pr_t\). | PhysicsAccuracy Lower \(Pr_t\) increases turbulent heat diffusion; higher values reduce it, changing wall/thermal-field predictions. | Use the default for general turbulent heat transfer; adjust only with justified data/model calibration. | Turbulent heat/species transport |
Wall treatment and wall distance
Wall treatment needs to be consistent with mesh resolution and the wall quantities of interest.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| All y+ Wall Functions (Kader blending)Default: Selected | Uses an all-\(y^+\) wall treatment that blends viscous-sublayer and logarithmic behavior; the thermal treatment uses Kader-type blending. | PhysicsAccuracyStability / convergence Allows a wider range of first-cell \(y^+\) than a pure log-law approach and changes wall shear/heat transfer. | General-purpose choice when mesh \(y^+\) varies across the wall. | Wall-function formulation |
| y+ Insensitive Wall Treatment | Uses the alternate wall treatment designed to reduce sensitivity to first-cell \(y^+\). | PhysicsAccuracy Changes near-wall closure and may improve robustness on meshes with nonuniform wall spacing. | Use when wall resolution varies strongly and compare wall quantities against the all-y+ treatment. | Wall-function formulation |
| Aero-thermal Heating Boundary Layer SolutionDefault: On | Enables the aerothermal boundary-layer heating treatment associated with wall heat-transfer prediction. | PhysicsAccuracy Can materially affect wall heat flux/temperature in high-speed boundary layers. | Keep enabled for aerothermal heating analyses unless a specific validation requires otherwise. | Thermal wall law |
| Cw+Default: 1/3 | Viscous-layer calibration constant in the wall treatment. | PhysicsAccuracy Changes viscous-layer blending and therefore wall shear/thermal transfer near the wall. | Keep the calibrated value unless performing model calibration. | Wall-function formulation |
| CexpDefault: 1.3 | Turbulent-layer blending exponent/calibration parameter. | PhysicsAccuracy Changes transition between viscous and turbulent wall-layer behavior. | Keep default for general use. | Wall-function formulation |
| Pr_twDefault: 0.85 | Wall turbulent Prandtl number used by the wall thermal treatment. | PhysicsAccuracy Controls turbulent heat transport in the near-wall closure. | Use default unless wall-heat-transfer calibration supports a different value. | Thermal wall law |
| Wall Distance: Direct SearchDefault: Alternative | Computes the shortest geometric distance from each cell to the relevant wall faces. | AccuracyCost Provides a direct geometric reference but can require more search work on very large meshes. | Use as a reference method when wall distance is especially critical or when comparing methods. | Wall-distance formulations |
| Wall Distance: Poisson Equation BasedDefault: Alternative | Obtains a smooth approximate wall-distance field from a Poisson-type auxiliary solve. Its iteration error is controlled by the convergence criterion and maximum-iteration fields. | AccuracyCostStability / convergence Can be efficient and smooth, but wall-function/turbulence results depend on convergence of the auxiliary distance solve. | Use when a PDE-based distance field is preferred; verify near corners and complex wall topology. | Wall-distance formulations |
| Poisson Convergence CriteriaDefault: 1e-5 | Relative or normalized stopping tolerance for the Poisson wall-distance solve. | AccuracyCost A smaller value performs a more complete distance solve and costs more iterations. If too loose, wall-distance error can propagate into y+, wall functions and turbulence terms. | The default is already tight for general use; change only after checking wall-distance sensitivity. | Wall-distance formulations |
| Poisson Maximum IterationDefault: 500 | Maximum number of Poisson wall-distance iterations. | AccuracyCostStability / convergence Limits auxiliary-solve cost. If the tolerance is not reached before this limit, the wall-distance field may be less converged than requested. | Increase only when the distance solve is still converging usefully at the cap. | Wall-distance formulations |
| Wall Distance: Fast MarchingDefault: Default | Propagates distance outward from wall-adjacent cells using the fast-marching procedure. | AccuracyCost Usually gives a low-cost wall-distance field suitable for large meshes. Complex topology should still be checked with y+ and wall-distance visualization. | This is the normal starting method. | Wall-distance formulations |
| Fast Marching Number of SweepsDefault: 1000 | Maximum propagation-sweep allowance for the fast-marching wall-distance calculation. | AccuracyCost More allowed sweeps increase worst-case work and give the propagation more opportunity to complete on difficult topology. | Keep the large default unless profiling shows it is unnecessary. | Wall-distance formulations |
Time physics and low-speed preconditioning
These physics-level controls work together with the Solution Control panel.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Time Physics: Steady-state | Targets a time-independent solution through pseudo-time/nonlinear iterations. | PhysicsCost Removes physical time evolution from the desired solution; convergence controls determine how accurately the steady state is reached. | Use when the physical solution is expected to be steady or a steady mean field is sufficient. | Steady/transient time formulation |
| Time Physics: Transient | Retains physical-time terms and advances the solution in time. | PhysicsAccuracyCost Captures unsteady physics; accuracy now depends on time step and temporal scheme as well as spatial discretization. | Use for inherently unsteady flow, SAS, transients, moving operating conditions or time-resolved loads. | Steady/transient time formulation |
| PreconditioningDefault: On | Modifies the pseudo-time/acoustic scaling at low Mach number to reduce stiffness while preserving the steady physical solution. | Stability / convergenceCost Can substantially accelerate convergence for low-Mach compressible flow. Incorrectly aggressive scaling can reduce robustness. | Normally keep enabled for low-Mach steady compressible cases. | Low-speed/pseudo-time preconditioning |
| Global Turkel FormulationDefault: On | Uses a global/average reference-Mach contribution in the low-speed preconditioning scale. | Stability / convergenceCost Changes preconditioning uniformity across the domain and may improve robustness when local Mach varies strongly. | Keep enabled unless local-only scaling is specifically desired for a validated case. | Low-speed/pseudo-time preconditioning |
| Unsteady PreconditioningDefault: On | Extends low-speed preconditioning so the physical time scale limits the amount of acoustic rescaling in transient dual-time calculations. | Stability / convergenceAccuracyCost Improves efficiency at low Mach while protecting physical-time accuracy. | Use for low-Mach transient compressible simulations with dual time stepping. | Low-speed/pseudo-time preconditioning |
| Ref Mach coefficient KPDefault: 1 | Scales the reference-Mach contribution used by preconditioning. | Stability / convergenceCost Larger values reduce the aggressiveness of low-speed acoustic scaling; smaller values can accelerate but make the system more sensitive. | Keep near the default unless a convergence study justifies adjustment. | Low-speed/pseudo-time preconditioning |
Species and volumetric reactions
Species options add composition transport and optional finite-rate chemistry.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Species TransportDefault: Off unless selected | Adds transport equations for independent species mass fractions, with the last fraction obtained from \(Y_{N_s}=1-\sum_{k=1}^{N_s-1}Y_k\). | PhysicsCost Adds equations, mixture-property coupling and diffusion; increases memory and CPU cost. | Enable only when composition changes are required. Define thermodynamic/transport data for every species. | Species conservation |
| Read mechanism file | Loads the reaction/species mechanism used for finite-rate chemistry. | PhysicsInitialization Defines reaction paths and kinetic rates; can strongly change heat release and composition. | Use a mechanism validated for the fuel/oxidizer, pressure and temperature range. | Chemistry/thermochemical input |
| Read thermodynamic data | Loads species thermodynamic property data used for caloric/chemical calculations. | PhysicsInitialization Changes mixture enthalpy, heat capacity, equilibrium/reverse-rate quantities and temperature coupling. | Use data consistent with the reaction mechanism. | Chemistry/thermochemical input |
| Print mixture / thermo / mechanism data | Reports the loaded mixture, thermodynamic or reaction data for verification. | Reporting / display No solution effect. | Use after import to verify species order, coefficients and reactions before a long run. | Chemistry/thermochemical input |
| No ReactionDefault: Selected when chemistry is not required | Transports species without homogeneous reaction source terms. | Physics Composition changes only by transport/diffusion/boundaries. | Use for mixing, nonreacting species transport or frozen chemistry. | Finite-rate chemistry |
| Turbulent Finite Rate | Combines Arrhenius finite-rate chemistry with turbulent mixing-rate limitation. | PhysicsCost Can limit reaction by either chemical kinetics or turbulence/mixing, affecting flame position and heat release. | Use for turbulent reacting flows when the model assumptions are appropriate. | Turbulent finite-rate closure |
| Laminar Finite Rate | Uses finite-rate Arrhenius chemistry without turbulent mixing-rate limitation. | PhysicsCostStability / convergence Reaction rate follows local kinetic state; can be stiff and expensive at high temperatures. | Use for laminar reacting flow or when turbulence-chemistry interaction is intentionally omitted. | Finite-rate chemistry |
Dispersed phase and IATE
These settings govern the separate dilute dispersed-phase model, not the homogeneous VOF model.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Dispersed Phase solutionDefault: Off | Enables the separate Eulerian dilute dispersed-phase equation set. | PhysicsCost Adds dispersed mass/momentum/thermal variables and interphase coupling. Cost and stiffness increase as IATE, breakup or coalescence closures are enabled. | Use for dilute particles or droplets that can slip relative to the carrier. It is distinct from homogeneous VOF. | Dispersed-phase model |
| Dispersed Flux: StandardDefault: Alternative | Uses the pressureless/standard dispersed convective flux without the regularized particle-pressure wave. | PhysicsStability / convergence Has the least artificial pressure support and therefore can be less robust where the dilute phase develops strong gradients or near-degenerate states. | Use only when the pressureless formulation is appropriate and stable for the case. | Dispersed-phase flux family |
| Dispersed Flux: RusanovDefault: Default | Uses a local Lax-Friedrichs/Rusanov-type flux based on the largest regularized dispersed wave speed. | Stability / convergenceAccuracy Adds dissipation but is normally the most robust starting flux for the dispersed equations. Sharp particle fronts can be more smeared than with less-dissipative alternatives. | Robust baseline for a dispersed-phase case; sharper fluxes are alternatives when front resolution matters. | Dispersed-phase flux family |
| Dispersed Flux: AUSMDefault: Alternative | Uses an AUSM-family advection/pressure split for the regularized dispersed system. | Stability / convergenceAccuracy Can reduce numerical diffusion relative to Rusanov while retaining pressure-like regularization. It can be more sensitive to state quality. | Use after the dispersed solution is robust and compare particle-front/diameter predictions. | Dispersed-phase flux family |
| Dispersed Flux: HLLCDefault: Alternative | Uses a contact-resolving HLLC-family approximate Riemann flux for the regularized dispersed system. | Stability / convergenceAccuracy Can sharpen contact-like structures but may be more sensitive to strongly dilute or poorly initialized regions. | Use as a flux-sensitivity option when sharper dispersed structures are required. | Dispersed-phase flux family |
| Particle pressure coefficient εpDefault: 1.0 | Upper coefficient of the regularized particle-pressure law. With face volume fraction \(\alpha_f\), the regularization is inactive for \(\alpha_f<\alpha_{fr}\). Otherwise each side uses \( arepsilon_{eff}=\min[ arepsilon_p,\,|\mathbf u_d|^2/(\gamma_p\rho_d^{\gamma_p-1}M_{min}^2)]\) and \(p_{fr}= arepsilon_{eff}\rho_d^{\gamma_p}\). | PhysicsStability / convergenceAccuracy Larger εp permits stronger pressure-like regularization and a larger artificial wave speed, often improving robustness but increasing numerical stiffness/dissipation. | Keep the calibrated default unless you are intentionally studying the dispersed regularization. | Packing/particle-pressure regularization |
| Particle pressure exponent γpDefault: 2.0 | Exponent in \(p_{fr}= arepsilon_{eff}\rho_d^{\gamma_p}\); the corresponding wave speed is \(c_d=\sqrt{ arepsilon_{eff}\gamma_p\rho_d^{\gamma_p-1}}\). | PhysicsStability / convergenceAccuracy Changes how rapidly regularized pressure/wave speed grows with dispersed density and therefore affects robustness and wave propagation. | Treat as a model parameter rather than a general convergence knob. | Packing/particle-pressure regularization |
| Minimum particle MachDefault: 2.0 | The regularization limits its artificial pressure so the dispersed wave speed is consistent with the configured minimum Mach scale \(M_{min}\). | Stability / convergenceAccuracy A larger value weakens the regularized wave speed for a given particle velocity; a smaller value permits stronger pressure support and can make the equations stiffer. | Keep the default unless a dedicated sensitivity study supports a change. | Dispersed-phase model |
| Minimum dispersed volume fraction αfrDefault: 0.0 | Threshold below which the regularized particle pressure and wave speed are switched off. | PhysicsStability / convergenceAccuracy A nonzero threshold confines pressure regularization to regions containing enough dispersed material. Too large a value can create an abrupt change in the dilute phase treatment. | The default leaves the regularization available down to vanishingly small positive loading; change only for a justified dilute-phase treatment. | Dispersed-phase model |
| Particle Packing LimitDefault: 0.63 | Maximum packing fraction used by dense-particle protection/closure logic. | PhysicsStability / convergence Limits the admissible concentration and affects closure protection as the dispersed phase approaches dense packing. | Set from the particle system/packing model and keep consistent with the numerical packing limit. | Packing/particle-pressure regularization |
| Minimum DiameterDefault: 1e-6 m | Lower admissible representative particle/droplet diameter. | PhysicsStability / convergenceAccuracy Prevents singular or extremely stiff drag/heat-transfer/area terms as diameter approaches zero. A larger floor can artificially suppress very small particles. | Choose a physical lower bound below the diameter range of interest but above numerically pathological values. | Dispersed-phase model |
| Minimum Particle DensityDefault: 1e-12 kg/m³ | Floor used when the transported dispersed density/loading becomes extremely small. | Stability / convergenceAccuracy Protects source terms and divisions in nearly empty regions. A large floor can add artificial dispersed material. | Keep the very small default unless a model-specific minimum is required. | Dispersed-phase model |
| High Order SolutionDefault: Off | Enables higher-order reconstruction for dispersed variables. | AccuracyStability / convergence Reduces numerical diffusion but increases sensitivity to sharp gradients, limiters and state admissibility. | Establish a stable first-order solution first, then enable for final accuracy and perform a mesh/order sensitivity check. | Dispersed-phase model |
| Interfacial Area TransportDefault: Off | Adds transport of interfacial area and characteristic-size evolution. | PhysicsCost Adds an equation and enables breakup/coalescence closures that change area and representative diameter. | Enable only when size evolution is required. Coalescence and turbulence-driven breakup need the corresponding prerequisites. | Interfacial-area transport |
| Particle CoalescenceDefault: On when available | Enables the IATE coalescence closure when its required physics is available. | PhysicsAccuracy Coalescence decreases interfacial area and increases representative particle/droplet size where the closure is active. | Requires dispersed phase + IATE + GE-RANS. The stored option is On by default, but has no effect until those prerequisites are active. | Coalescence model |
| Coalescence constant C1Default: 0.188 | First calibration coefficient of the turbulence-driven coalescence closure. | PhysicsAccuracy Changes collision/coalescence source strength and therefore predicted interfacial area/diameter. | Retain the calibrated default unless experimental size data justify a change. | Coalescence model |
| Coalescence constant C2Default: 1.29 | Second calibration coefficient of the turbulence-driven coalescence closure. | PhysicsAccuracy Changes the coalescence efficiency/rate response and therefore characteristic size. | Retain the calibrated default unless calibrating the closure. | Coalescence model |
| Particle BreakupDefault: On when available | Enables the primary breakup contribution to the IATE source. | PhysicsAccuracy Breakup increases interfacial area and reduces representative size where the breakup criterion/source is active. | Requires IATE. The stored option is On by default but is inactive without IATE. | Acceleration-driven breakup |
| Breakup time constant CτDefault: 0.5 | Calibration coefficient controlling the characteristic breakup time scale. | PhysicsAccuracyStability / convergence Changing it changes how rapidly breakup alters interfacial area and size, and can also change source-term stiffness. | Keep the default unless closure calibration is supported by data. | Acceleration-driven breakup |
| Breakup radius constant CRTDefault: 0.1 | Calibration coefficient controlling the size/radius relation used by the breakup model. | PhysicsAccuracy Changes the resulting characteristic-size response of breakup. | Keep the default unless calibrating against diameter data. | Acceleration-driven breakup |
| Self BreakupDefault: On when available | Enables the self/acceleration breakup mechanism when IATE is active. | PhysicsAccuracy Adds breakup driven by body-force/surface-tension competition and can increase interfacial area even without the turbulence-impact mechanism. | Requires IATE. Use only when the physical mechanism is applicable. The stored option is On by default. | Gravity/Eötvös breakup |
| Critical Eötvös number EoCRTDefault: 1.0 | Threshold parameter used by the self-breakup criterion. | PhysicsAccuracy Changes when acceleration/surface-tension conditions are strong enough to activate self-breakup. | Use a value appropriate to the breakup model calibration. | Gravity/Eötvös breakup |
| Reference gravity gCRTDefault: 9.81 m/s² | Gravity/acceleration scale used with the self-breakup criterion. | PhysicsAccuracy Changes the acceleration scale entering the critical breakup condition. | Use the physical reference acceleration expected by the calibrated model. | Gravity/Eötvös breakup |
| Turbulent Impact BreakupDefault: On when available | Enables turbulence-driven breakup when the required turbulence and IATE variables are available. | PhysicsAccuracy Can strongly increase interfacial area and reduce characteristic diameter in energetic turbulent regions. | Requires dispersed phase + IATE + GE-RANS. The stored option is On by default, but is inactive without those prerequisites. | Turbulent-impact breakup |
| Turbulent breakup constant ΓBDefault: 0.264 | Calibration coefficient in the turbulence-impact breakup source. | PhysicsAccuracy Directly changes breakup source magnitude and therefore predicted area/diameter. | Retain the calibrated default unless experimental data support adjustment. | Turbulent-impact breakup |
| Turbulent breakup constant KBDefault: 1.37 | Second calibration coefficient in the turbulence-impact breakup model. | PhysicsAccuracy Changes the turbulence-breakup response and can alter the threshold/rate of size reduction. | Retain the calibrated default unless performing a validated closure calibration. | Turbulent-impact breakup |
Homogeneous VOF
VOF controls the homogeneous multiphase formulation and interface-capturing method.
| GUI option | Meaning / formulation | Effect on the simulation | Practical guidance | Theory reference |
|---|---|---|---|---|
| Enable homogeneous VOFDefault: Off unless selected | Enables a homogeneous one-fluid mixture with phase fractions. For \(N\) phases CMPS solves \(N-1\) independent fractions and computes \(\alpha_N=1-\sum_{k=1}^{N-1}\alpha_k\). | PhysicsCost Adds composition-dependent mixture properties and interface transport. All VOF constituents share the same velocity, pressure and temperature. | Use for immiscible phases represented by one homogeneous momentum/energy field. | Homogeneous VOF model |
| VOF Interface: UpwindDefault: Legacy/unconfigured fallback | Uses first-order upwind transport for phase fractions. | AccuracyStability / convergence Most robust and most diffusive; interfaces broaden as they are convected. | Use for difficult initialization or as a fallback when interface-compressive methods are unstable. | VOF interface/phase flux |
| VOF Interface: HRICDefault: Default for a new VOF setup | Uses a bounded high-resolution interface-compressive transport method. | AccuracyStability / convergence Maintains a sharper interface than Upwind, with greater sensitivity to mesh quality and Courant number. | This is the normal new-case starting choice; verify interface sharpness and boundedness. | VOF interface/phase flux |
| VOF Interface: CICSAMDefault: Transient only | Uses the CICSAM interface-capturing method. | AccuracyStability / convergence Can give sharp transient interface transport but is more sensitive to time step/Courant number and mesh quality. | Available for transient VOF only. Perform time-step and mesh sensitivity checks. | VOF interface/phase flux |
| Phase Count | Sets the total number \(N\) of homogeneous VOF phases. | PhysicsCost Adds \(N-1\) independent fraction unknowns and increases mixture-property coupling/cost. | Use only the phases physically required. | VOF variables and phase definition |
| Reference Phase | Selects the dependent phase fraction \(\alpha_N\), reconstructed from the simplex constraint. | Stability / convergenceAccuracy Does not change the continuum physics, but changes which fraction is not solved independently and can affect numerical conditioning near vanishing phases. | Choose a convenient reference phase and keep all BC/IC fractions consistent. | VOF variables and phase definition |
| Phase Identifier / Material | Assigns a material/EOS/property model to each VOF phase. | PhysicsInitialization Directly changes mixture density, energy, sound speed, viscosity, conductivity and compressibility regime. | Verify every phase material and EOS before initialization. | VOF variables and phase definition |
| Apply VOF setup | Commits the displayed VOF phase definition and interface method. | InitializationPhysics Changes the active equation set/mixture definition used by subsequent initialization and solution. | Apply only after all phase assignments and the reference phase are correct. | Homogeneous VOF model |
| Reload VOF setup | Restores/reloads the currently committed VOF configuration and discards uncommitted edits. | No physical change if used only to discard edits. | Use when you want to undo unsaved VOF-panel changes. | Homogeneous VOF model |