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You can also plot axial velocity profiles at x = 1 m, 2 m, 3 m, 4 m, 5 m and 6 m as shown below. The numbers of the lines also indicate the distances from the expansion entrance to these lines.

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As you can see from the velocity profiles, the end of the recirculation region is at x = 5 m. In other words, the recirculation length for Re = 55.4 is about 5 times of the inlet radius, which agree well with the experimental data (Hammad et al., Experiments in Fluids, 1999, 26:266-271) shown below.

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