Encyclopaedia Index

## Cylindrical-polar coordinates

### Activation

Cylindrical-polar coordinates are activated by setting CARTES=F in the Q1 file.

To switch between the co-ordinate systems in the VR-Editor, click on **Menu /
Geometry**, then on Co-ordinate system. The Cartesian grid is the default.

Image: Grid Mesh Settings Dialog

The change between Cartesian and Cylindrical-polar can be made at will in either
direction.

- The X-direction is now the circumference, q, measured in
radians.
- The Y-direction is the radius, r, measured in metres.
- The Z-direction is the axis, z, measured in metres.

The inner radius of the domain is set via RINNER. This sets the distance from
the axis of symmetry to the cylinder y=0.

The origin of the polar system is at the origin of the cartesian system. The Z axis is
common to both. When the polar X=0, the Y axis aligns with the cartesian Y. When looking
along Z towards the origin with Y pointing up, X increases in the clock-wise direction, as
shown below:

### VR Objects in Polar Coordinates

The treatment of object size is described here, and object
position here.

To summarise, the position of the bounding box origin is **always** set in
polar coordinates. The size can be in polar coordinates (whenever a default geometry is
used), **or** in cartesian coordinates (whenever a non-default geometry is
used). This allows objects to either follow the grid when they change size, or to keep
their proper shapes.

The image below shows two objects, both with their X and Y sizes set to 0.5.

Image: Object geometries for Polar

### PARSOL and Polar Coordinates

PARSOL works correctly in polar coordinates.

Image: Flow past a wedge in Polar coordinates

Please bear in mind that the grids get progressively bigger with increasing radius so
the chance of finding multiply-cut (and hence illegal) cells also increases.