The model inputs for mixing planes are presented in this section. Only those steps relevant specifically to the setup of a mixing plane problem are listed here. Note that the use of wall and periodic boundaries in a mixing plane model is consistent with their use when the model is not active.
| When the density-based solver is enabled, only the
Absolute Velocity Formulation can be used with the mixing plane model.
Define Models Solver...
Define Boundary Conditions...
Details about these inputs are presented in Section 7.17.1 for fluid zones, and in Section 7.18.1 for solid zones.
| It is important to define the axis of rotation for the cell zones on
both sides of the mixing plane interface, including the stationary zone.
Details about these inputs are presented in Sections 7.3.1, 7.4.1, and 7.5.1.
| Note that the outlet boundary zone at the mixing plane interface must be defined as a pressure outlet, and the inlet boundary zone at the mixing plane interface must be defined as a velocity inlet (incompressible flow only), a pressure inlet, or a mass flow inlet. The overall inlet and exit boundary conditions can be any suitable combination permitted by the solver (e.g., velocity inlet, pressure inlet, or mass flow inlet; pressure outlet). Keep in mind, however, that if mass conservation across the mixing plane is important, you need to use a mass flow inlet as the downstream boundary; mass conservation is
not maintained across the mixing plane when you use a velocity inlet or pressure inlet.
Define Mixing Planes...
A Radial geometry signifies that information at the mixing plane interface is to be circumferentially averaged into profiles that vary in the radial direction, e.g., , . This is the case for axial-flow machines, for example.
An Axial geometry signifies that circumferentially averaged profiles are to be constructed that vary in the axial direction, e.g., , . This is the situation for a radial-flow device.
| Note that the radial direction is normal to the rotation axis for the fluid zone and the axial direction is parallel to the rotation axis.
In 2D the flow data is averaged over the entire interface to create a profile consisting of a single data point. For this reason you do not need to set the number of Interpolation Points or select a Mixing Plane Geometry in 2D.
where is the under-relaxation factor. Once the flow field is established, the value of can be increased.
If you create an incorrect mixing plane, you can select it in the Mixing Plane list and click the Delete button to delete it.
There are two options available for use with the mixing plane model: a fixed pressure level for incompressible flows, and the swirl conservation described in Section 10.3.2.
Fixing the Pressure Level for an Incompressible Flow
For certain turbomachinery configurations, such as a torque converter, there is no fixed-pressure boundary when the mixing plane model is used. The mixing plane model is usually used to model the three interfaces that connect the components of the torque converter. In this configuration, the pressure is no longer fixed. As a result, the pressure may float unbounded, making it difficult to obtain a converged solution.
To resolve this problem, FLUENT offers an option for fixing the pressure level. When this option is enabled, FLUENT will adjust the gauge pressure field after each iteration by subtracting from it the pressure value in the cell closest to the Reference Pressure Location in the Operating Conditions panel.
| This option is available only for incompressible flows calculated using the pressure-based solver.
To enable the fixed pressure option, use the fix-pressure-level text command:
define mixing-planes set fix-pressure-level
Conserving Swirl Across the Mixing Plane
As discussed in Section 10.3.2, conservation of swirl is important for applications such as torque converters. If you want to enable swirl conservation across the mixing plane, you can use the commands in the conserve-swirl text menu:
define mixing-planes set conserve-swirl
To turn on swirl conservation, use the enable? text command. Once the option is turned on, you can ask the solver to report information about the swirl conservation during the calculation. If you turn on verbosity?, FLUENT will report for every iteration the zone ID for the zone on which the swirl conservation is active, the upstream and downstream swirl integration per zone area, and the ratio of upstream to downstream swirl integration before and after the correction.
To obtain a report of the swirl integration at every pressure inlet, pressure outlet, velocity inlet, and mass flow inlet in the domain, use the report-swirl-integration command. You can use this information to determine the torque acting on each component of the turbomachinery according to Equation 10.3-4.
Conserving Total Enthalpy Across the Mixing Plane
One of the options available in the mixing plane model is to conserve total enthalpy across the mixing plane. This is a desirable feature because global parameters such as efficiency are directly related to the change in total enthalpy across a blade row or stage.
The procedure for ensuring conservation of total enthalpy simply involves adjusting the downstream total temperature profile such that the integrated total enthalpy matches the upstream integrated total enthalpy.
If you want to enable total enthalpy conservation, you can use the commands in the conserve-total-enthalpy text menu:
define mixing-planes set conserve-total-enthalpy
To turn on total enthalpy conservation, use the enable? text command. Once the option is turned on, you can ask the solver to report information about the total enthalpy conservation during the calculation. If you turn on verbosity?, FLUENT will report at every iteration the zone ID for the zone on which the total enthalpy conservation is active, the upstream and downstream heat flux, and the ratio of upstream to downstream heat flux.