Hybrid Initialization is a collection of recipes and boundary interpolation methods. It solves the Laplace equation to produce a velocity field that conforms to complex domain geometries, and a pressure field which smoothly connects high and low pressure values in the computational domain. All other variables (that is temperature, turbulence, VOF, species, and so on) will be patched based on domain averaged values or a predetermined recipe. These recipes are detailed below.
Velocity Field: Laplace's equation is solved with appropriate boundary conditions to produce the velocity field in the domain.
(23–149)
where
is the velocity potential. The velocity
components are given by the gradient potential:
(23–150)
Velocity potential is expressed as follows for the various boundary conditions:
Wall Boundaries: The velocity normal to the wall is zero.
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Inlet Boundaries: The velocity normal to the inlet boundaries are computed from the user-specified boundary values.
(23–152)
Far Field Boundaries: At the far-field boundaries the velocity normal to the boundaries is computed from the user-specified free stream conditions.
(23–153)
Far away from the body the flow approaches the free stream conditions:
(23–154)
(23–155)
(23–156)
Outlet Boundaries: They are specified as zero potential.
(23–157)
A uniform initial velocity magnitude with the direction taken from the solution of the velocity potential solution can be specified by selecting the Maintain Constant Velocity Magnitude option under the General Setting tab.
Pressure Field: An additional Laplace equation is solved with the appropriate boundary condition to produce the smooth pressure field in the domain, only if the pressure information is available in at least one inlet and one outlet in the domain. Otherwise, the pressure field will be initialized with the averaged constant value from all the boundaries.
(23–158)
where
is expressed as follows for the
various boundary conditions:Pressure inlet boundaries: by default, first an approximate check is made to determine whether the boundary flow is supersonic or subsonic, where a large difference between the specified Gauge Total Pressure and Supersonic/Initial Gauge Pressure corresponds to supersonic flow, and a moderate / small (or zero) pressure difference corresponds to subsonic flow. When a boundary is determined to be supersonic, then
uses the value of the specified Supersonic/Initial Gauge
Pressure; when the boundary is determined to be subsonic, then uses the value of the specified Gauge Total Pressure.
If you enabled the Use Specified Pressure on Inlets option in the
General Settings tab of the Hybrid Initialization
dialog box, then always uses the specified Supersonic/Initial Gauge
Pressure.Pressure outlet and Pressure Far-Field boundaries:
is computed as the specified Gauge Pressure at this
boundary.Velocity/Mass-flow inlet boundaries:
uses the value of the specified Supersonic/Initial Gauge
Pressure only if you have selected the Use specified pressure on the
inlet option under the General Settings tab. Wall Boundaries: the normal gradient of
is set
to zero.
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Temperature Field: Temperature will be initialized with a constant value (domain averaged).
Turbulent Parameters: By default, turbulent parameters are initialized with constant values (domain averaged). However, if you want to initialize the flow with variable turbulence parameters, then you will need to select the appropriate option in the Hybrid Initialization dialog box, described in Steps in Using Hybrid Initialization.
Species Fractions: By default, secondary species mass/mole fractions are initialized with a 0.0 value. However, if you want to specify the initialization values, then you will need to select the appropriate option in the Hybrid Initialization dialog box, described in Steps in Using Hybrid Initialization.
Volume Fractions: For a two-phase case, the secondary VOF phase will be initialized with the minimum VOF from all inlets. If the case has more than two phases, then the secondary phases will be initialized with a zero VOF.
For information about using hybrid initialization in Ansys Fluent, see Hybrid Initialization in the User's Guide.