Parameter space tested by the experiments. The roman numerals give the different drag regimes explained in Sect. 2. The red line shows the drag regime of the characteristic radius of the aggregates of ≈ 13 mm (see Table 1). The colored lines show the drag regime of the substructures used, as indicated in the figure legend. Here Kn and Re are calculated with different characteristic sizes L. The aggregates are associated with two different sizes and can therefore be affected by different flow regimes.