ANGLED-PLATE objects

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 to flow.
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.
pressures velocities

Case 2: The upstream flow is horizontal and the plate inclined.
The pressure increases on the upstream side of the plate and falls on the downstream side.
The fluid is strongly deflected; and a recirculation region appears on its downstream side.
pressures velocities

Case 3: The upstream flow is horizontal and the plate inclined at a smaller angle.
The pressure increases and decreases are smaller, as is the size of the recirculation region.
pressures velocities

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.
pressures velocities

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.
pressures velocities

2. Further developments

The angled-plate feature can be developed further in the following respects:

Curved plates can be simulated by the use of shapes already present in the d_object directory and its sub-folders, for example the 'half-cylinder'.
Shapemaker can be employed so as to create a 'generalised wedge' shape, formed by intersection of a grid-fitting hexagon with an arbitrarily-inclined plane.
The display of the flow can be improved, both in PHOTON and the VR Viewer.
Greater attention to the equations solved for the near-cut-cell pressures and velocities will bring increased conformity with physical reality.
The angled plate object needs to be endowed with further attributes, such as:
- 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.