1. The general idea
It is frequently desired to represent the influence on the flow of a thin
surface which is inclined to the computational grid; and often this
surface is plane. Common examples are:
- a partly-open door;
- a horizontally-hinged window or trap-door;
- a pitched roof; and
- an obliquely-placed wind-screen.
Many such requirements can be met by:
- placing within the flow a three-dimensional wedge-shaped object;
- moving and re-sizing it so that its inclined surface coincides
with the position of the desired thin plate;
- arranging that its other
surfaces coincide with the surfaces of cells of the grid;
- assigning to the wedge-shaped object a material-identification
index (in PHOENICS terms, a PRPS value) of 299; and
- setting PARSOL = T (which is in any case its default value) in the
data-input file, Q1.
The effect of these actions is as follows:
- PHOENICS at first treats the object as solid, and so computes the
geometry of the obliquely-cut cells.
- It sets to zero, or otherwise shrinks, the cut-cell areas and
volumes, thus in effect treating the cell-cutting surface as impervious
- Having done so, it notes that the PRPS value is 299 and resets it
to -1, which indicates 'domain material'. If the open cells of the object are to
be filled with some material other than the current domain material, then the
material index should be set to 300+imat. Note that the
PROPS file must then contain
this material number. Earth will then reset PRPS by subtracting 300 to recover
the desired material number.
- Cells in both side of the cut surface are then treated as containing
domain fluid; but the cut surface acts as an obstacle.
2. An Example
Input-File Library Case
v206 provides an example, some results of which are shown here.
Case 1: The flow is aligned with the plate; therefore the pressure drop
which it causes is very small, the effect on the flow direction likewise.
Case 2: The upstream flow is horizontal and the plate inclined.
pressure increases on the upstream side of the plate and falls on the
The fluid is strongly deflected; and a recirculation region appears on
its downstream side.
Case 3: The upstream flow is horizontal and the plate inclined at a
The pressure increases and decreases are smaller, as is the size of
the recirculation region.
Case 4: The upstream flow is horizontal and the plate inclined so that
the stream impinges on its lower side.
The pressure and velocity fields mirror those of case 3.
Case 5: The upstream flow is horizontal; and there are now two plates
positioned so as to simulate a pitched roof.
There are two recirculation regions; and the lowest pressure is on
the space below the plates.
2. Further developments
The angled-plate feature can be developed further in the following
- Curved plates can be simulated by the use of shapes already present
in the d_object directory and its sub-folders, for example the
- Shapemaker can be employed so as to create a 'generalised wedge'
shape, formed by intersection of a grid-fitting hexagon with an
- The display of the flow can be improved, both in PHOTON and the VR
- Greater attention to the equations solved for the near-cut-cell
pressures and velocities will bring increased conformity with physical
- The angled plate object needs to be endowed with further attributes,
- partial permeability,
- finite thermal conductivity (at present it is impervious to heat).
- sources of heat, mass and momentum.
These developments will form part of the NewParsol project.