The High Mach Number Reacting Flow Coupling Feature
Use the High Mach Number Reacting Flow () multiphysics coupling to simulate mass transport and reactions in a gas mixture where the fluid flow can be dependent on the mixture composition.
The coupling automatically accounts for the heat of reaction, enthalpy diffusion and contributing mass fluxes.
Select a Fluid Flow interface and a Species transport interface to couple fluid flow with mass transport. Chemistry is optional, and if it is selected, the fluid properties are taken from the Chemistry interface.
The pressure, velocity, and temperature variables of the High Mach Number Reacting Flow coupling node are set to the Common Model Input values of the Default Model Inputs node on the complementary selection, that is, all domains except those from the Selection list. It allows to couple multiple fluid flow or transport of species interfaces with a single heat transfer interface. See Default Model Inputs in the COMSOL Multiphysics Reference Manual for details.
Domain Level Synchronization
The High Mach Number Reacting Flow coupling synchronizes the features from a High Mach Number Flow interface, a Transport of Concentrated Species interface and, optionally, a Chemistry interface. When the Chemistry interface is not selected, the density in the High Mach Number Flow interface is automatically synchronized to the one defined by the Transport of Concentrated Species interface.
The velocity field used by the Transport of Concentrated Species interface is synchronized to the one computed in the High Mach Number Flow interface.
When a Chemistry interface is selected, the High Mach Number Reacting Flow coupling synchronizes the definition of the thermal conductivity, density, heat capacity, enthalpy, molar mass and dynamic viscosity with the other coupled physics interfaces. The reference temperature is taken from the High Mach Number Flow interface.
The Stefan Velocity
The High Mach Number Reacting Flow coupling feature automatically couples mass transfer on boundaries and applies a corresponding velocity contribution for the flow. Prescribing a net mass boundary flux in the Transport of Concentrated Species interface, either using a Flux or Mass Fraction feature, the High Mach Number Reacting Flow feature computes The Stefan Velocity and applies this in Wall features using the same selection.
Turbulent Mass Transfer
When a turbulence model is used, the High Mach Number Reacting Flow coupling applies turbulence modeling for the mass transport in the following manners:
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Turbulent mass transport is added, defined from the turbulent viscosity and a turbulent Schmidt number (for more information, see Turbulent Mass Transport Models).
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Mass transport wall functions. When a turbulence model using wall functions is used for the fluid flow, the High Mach Number Reacting Flow coupling automatically adds wall functions for the mass transport on the same boundaries (for more information, see Mass Transport Wall Functions).
Settings
The Label is the default multiphysics coupling feature name.
The Name is used primarily as a scope prefix for variables defined by the coupling node. Refer to such variables in expressions using the pattern <name>.<variable_name>. In order to distinguish between variables belonging to different coupling nodes or physics interfaces, the name string must be unique. Only letters, numbers, and underscores (_) are permitted in the Name field. The first character must be a letter.
The default Name (for the first multiphysics coupling feature in the model) is hmnrf1.
Domain Selection
The High Mach Number Reacting Flow coupling is automatically defined on the intersection of the selections for the coupled interfaces.
The Selection list displays the domains where the coupling feature is active.
Coupled Interfaces
This section defines the physics involved in the multiphysics coupling. The Fluid flow, Species transport, and Chemistry lists include all applicable physics interfaces.
The default values depend on how this coupling node is created.
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If it is added from the Physics ribbon (Windows users), Physics contextual toolbar (Mac and Linux users), or context menu (all users), then the first physics interface of each type in the component is selected as the default.
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If it is added automatically when a multiphysics interface is chosen in the Model Wizard or Add Physics window, then the participating physics interfaces are selected.
You can also select None from a list to uncouple the node from a physics interface.
Click the Go to Source buttons () to move to the main physics interface node for the selected physics interface.
Click the Show or Hide Physics Properties Settings button () to toggle the display of physics properties settings affecting the coupling feature. When a turbulence model is used, turbulent mass transfer is automatically accounted for (see the settings in the Turbulence section below). Using High Mach Number Reacting Flow coupling, the mass transfer treatment at walls follows that applied for the fluid flow. Therefore the Wall treatment setting is also displayed when using a turbulence model. For more information on turbulent mass transfer at walls, see the section Mass Transport Wall Functions in the CFD Module User’s Guide.
If a physics interface is deleted and then added to the model again, then in order to reestablish the coupling, you need to choose the physics interface again from the Fluid flow, Species transport and Chemistry lists. This is applicable to all multiphysics coupling nodes that would normally default to the once present interface. See Multiphysics Modeling Workflow in the COMSOL Multiphysics Reference Manual.
Mass transport Turbulence model
When the fluid flow interface uses a turbulence model, select an option from the Mass transport turbulence model list — Kays-Crawford or User-defined turbulent Schmidt number.
For User-defined turbulent Schmidt number, enter a Turbulent Schmidt number ScT (dimensionless).
The turbulent mass transfer added to the mass fraction equations is defined as, , where, μT is the turbulent viscosity defined by the flow interface, and the turbulent Schmidt number, ScT, depends on the Mass transport turbulence model used.
The Turbulence model type used by the fluid flow interface can be displayed by selecting the Show or Hide Physics Property Settings button at the right of the Fluid flow list.