Post-processing

When the calculations are finished, the message Process '…', started on … has finished. is displayed. Then we can proceed to visualising the results by pressing Postprocess (therefore the problem must still be loaded; should this not be the case we first have to open the problem files again).

As the post-processing options to be used are the same as in the previous examples, they will not be described in detail here again. For further information please refer to the Post-processing chapter of example 1 and to the Pre/postprocessor user manual or online help.

The results given below correspond to the last time step of t = 100s.

Figure 61 Velocity module distribution

Figure 62 Velocity contour lines, detail

Figure 63 Velocity vectors

Figure 64 Velocity vectors, detail

Figure 65 Pressure distribution

We can verify the numerical results by comparing them with experimental and other numerical results. At this low Reynolds number for which the example is calculated, only the first vortex of Figure 66 will develop, so the parameter that can be verified easily is x1. At Re = 250, the experimental values available for x1 lie between x1 = 5 - 6.s [1], while other numerical results available report x1 = 5.0 s [[6],[7]].

Figure 66 Characteristic lengths for the
backward-facing step problem

Figure 67 shows the computed characteristic length x1 in GiD length units (m). We obtain x1 = 5.8 s, which is a reasonably good result for the coarse mesh used.

Figure 67 Characteristic length obtained in the analysis