**6. Experiments**

For the experiments, the magnetic valve for the forced air flow was connected to the projecting sequence of the measurement system using a software trigger. To ensure a fully developed air flow field and account for triggering delays, the projection of the first image was delayed by *td*,<sup>0</sup> = 0.3 s compared to the opening of the magnetic valve. The measurement sequence started with a measurement without the air flow and was followed by a measurement with an active flow system to reduce the effect of cooling on the analysis and ensure a fully developed refractive index field during the measurement without forced air flow.
