# Post-processing in CFD is really fun!

In this blog, common types of post-processing tools are discussed briefly:

**X-Y plots**

These are simple, two-dimensional graphs. They can be drawn by hand or by many plotting packages. They are the most precise and quantitative way to present numerical data and, since laboratory data is often gathered by straight-line traverses, they are a popular way of making a direct comparison between experimental and numerical data.

One way of visualising the development of the flow is to use several successive profiles.

**Contours**

A ‘Shaded Contours’ is an excellent tool for conveying information and good for on-screen and presentational analysis of data. Simple packages flood the region between iso-lines with a fixed colour for that interval. The most advanced packages allow a pixel-by-pixel gradation of colour between values specified at the cell vertices, together with lighting and other special effects such as translucency.

A ‘Line Contour’ is a line along which some property is constant. The equivalent in 3 dimensions is an “isosurface”. Any field variable may be contoured. In contrast to X-Y plots, contour plots give a global view of the flow field, but are less useful for reading off precise numerical values. If the domain is linearly scaled then detail occurring in small regions is often obscured.

**Vector plots**

Vector plots display vector quantities (usually velocity; occasionally stress) with arrows whose orientation indicates direction and whose size (and sometimes colour) indicates magnitude. They are a popular and informative means of illustrating the flow field in two dimensions, although if grid densities are high then either interpolation to a uniform grid or a reduced set of output positions are necessary to prevent the number density of arrows blackening the plot.

**Streamlines**

Streamlines are parallel to the mean velocity vector and are very useful in showing the direction of any fluid particle within the domain.