FREE.HTM

FREE-SURFACE-FLOW simulation in PHOENICS

FREE-Surface Flows (ie flows that involve the presence and interaction of two or more fluids, separated by sharply defined interfaces) can be simulated by PHOENICS. Two different methodss are provided, namely:

the Scalar Equation Method (SEM);
the Height of Liquid (HOL)technique.

Both HOL and SEM employ a one-velocity-set solution procedure, and the different fluids separated by the distinct interface have only one value of each velocity component, temperature, concentration, etc for each computational cell. The relevant governing equations are solved in the conventional single-phase manner and the two fluids are accounted for through the specification of the physical properties (density, viscosity, etc).

The applicability and limitations of these options can be summarized as follows:

The SEM technique deduces the interface position from the solution of a conservation equation for a scalar "fluid-marker" variable, and in this respect can suffer from numerical diffusion in coarse grids. The SEM is applicable to unsteady incompressible flows only, in one-, two- or three- dimensions. It can simulate convoluted and overturning surfaces. Since the SEM employs a fully explicit formulation it is constrained by the Courant criterion for time-step increment for the stability of the solution. The SEM generally works well for highly non- orthogonal grids with NONORT set to TRUE. It can also cope with heat transfer between the fluids, and with conjugate heat transfer between the fluids and surrounding and immersed solids.
See the entry on S-E-M (Scalar Equation Method) for instructions on how to activate it.
The HOL method determines the location of the interface from the solution of the liquid-balance equations. The HOL method is applicable to both steady and unsteady incompressible isothermal flows, in one-, two- or three-dimensions. It is restricted to flows that are not convoluted (in interconnected blocked regions for example) and exhibit no "overturning" of the interface. The HOL method is fully implicit and therefore suffers no restrictions, for unsteady cases, on the time-step increments. The HOL method does not generate numerical diffusion which implies less emphasis on grid-size constraints. However, for highly non-orthogonal grids convergence problems may occur with the HOL method.

See the entry for H-O-L for instructions on how to activate it in PHOENICS.

FREE-Surface Flows

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>>> See the Encyclopaedia entry 'Free-surface flows'.

FREEE

----- PIL real flag; value=9.0; group 13 - -

FREEE....is a PATCH type used for setting sources per unit FREE East area by way of COVAL in group 13.

Note that 'FREE' here signifies the cell-face area available for flow, (i.e. the geometrical area multiplied by the cell-face porosity). The types FREEE, FREEN, FREEH and FREEVL should be used only for cell faces internal to the domain, i.e. east faces of cells at IX=1 to NX-1, for north faces of cells at IY=1 to NY-1 and high faces of cells at IZ=1 to NZ-1. Cell faces at boundaries should be specified by use of the EAST, NORTH, and HIGH types, as appropriate.

FREEH

----- PIL real flag; value=11.0; group 13 -

FREEH....is a PATCH type used for setting sources per unit FREE High area by way of COVAL in group 13. See FREEE for further information.

FREEN

----- PIL real flag; value=10.0; group 13 -

FREEN....is a PATCH type used for setting sources per unit FREE North area by way of COVAL in group 13. See FREEE for further information.

FREEVL

---- PIL real flag; value=12.0; group 13 -

FREEVL....is a PATCH type used for setting sources per unit FREE VoLume by way of COVAL in group 13. See FREEE for further information.

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