# Spectral analysis

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In this part we will analysis the Strouhal number and the kelvin Helmholtz instability by the frequency. We have defined 8 monitor points in order to calculate the evolution of the physical parameters on the defined points ( especially the pressure).

Here we have chosen a horizontal line, since the wake moves periodically and alternatively, so the horizontal line is the average position of the wake.

Figure 3.4 – Position of the monitor points

In the TABLE 3.1. are the coordinates of the eight monitor points. The block and the coordinate (k, i and j) are defined in the mesh reference of the NSMB.

 monitor point block k i j 1 13 1 83 12 2 13 1 64 26 3 13 1 55 30 4 13 1 45 36 5 13 1 39 41 6 5 1 6 22 7 5 1 11 24 8 5 1 20 28

Table 3.1 – Coordinates of the monitor points

Then we will use the FFT approach to observe the variation of the PSD as a function of the St ( dimensionless value of the frequency ).