4.10.3. Wall

A wall boundary is a boundary through which no advective mass flux is allowed. The wall itself can be stationary, or have a specified velocity tangential to the flow. It can be isothermal, or have a specified wall_temperature, for simulations including an enthalpy equation.

begin wall boundary condition on surface surface_4
    wall_temperature = 400
end

If you specify a value on the wall for a mass fraction, mixture fraction, or progress variable there will be a dirichlet boundary condition applied on the wall nodes for that scalar, which means that there will be diffusion of that scalar through the wall. If this is not desired, do not specify a value on the wall boundary condition.

The complete list of available commands for the wall boundary condition and the syntax for the different options can be found in Wall Boundary Condition On Surface.

4.10.3.1. Turbulent Wall Modeling

Wall-modeled (as opposed to “wall-resolved”) turbulent simulations use a boundary layer model at the wall. The choice of whether a wall model is used is defined in the Turbulence Model block in Solution Options. There are two wall-model related options one can specify per boundary. They are Use equilibrium production model, which sets the rule that turbulent production and dissipation are equal at the wall, and law_of_wall_roughness_parameter, which sets a dimensionless roughness parameter used in the wall models ( $E$ , default is 9.8). For more details, see the wall modeling section in the theory chapter.

begin wall boundary condition on surface surface_4
    # ...
    Use equilibrium production model
    law_of_wall_roughness_parameter = 9.8
end

4.10.3.2. Conjugate Heat Transfer

When a wall provides a conjugate heat transfer interface to Sierra/Aria, you can indicate this with the interface boundary command. This signals to Fuego that wall_temperature will be supplied via a transfer from an external region.

begin wall boundary condition on surface surface_4
    # ...
    Interface boundary
end

4.10.3.3. Convection Coefficients

By default Fuego calculates linearized flux terms (flux_linearization_coefficient and flux_linearization_temperature) on the wall in a form that resemble a convection equation, but using a near-wall temperature instead of a far-field reference temperature. This means that the coefficient $C$ here will be mesh-dependent, and will not correspond to an expected convection coefficient from a correlation.

(4.29) $q = C (T_{\rm{near,wall}} - T_{\rm{wall}})$

For comparison with a conventional correlation for $h$ one would want something of the form

(4.30) $q = h ( T_{\rm{ref}} - T_{\rm{wall}})$

Fuego has a special post-processor for calculating $h$ in this manner on the wall boundaries, with a user=specified $T_{\rm{ref}}$ . This will produce a wall_convection_coefficient nodal field that can be output to Exodus or used in other post-processors.

begin wall boundary condition on surface surface_4
    # ...
    Calculate Convection Coefficient using Tref = 350
end