Author(s): J.-L. Boillat; W. H. Graf

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Abstract: To study the influence of turbulence on settling velocities an experimental set-up was developed, creating a homogeneous and isotropic turbulence. The principal elements of the installation are given; see Figures 1 to 3. Subsequently is presented the measuring technique; hot-film anemometry is used to measure the turbulence and a videoequipment to study the settling characteristics. The results of the turbulence study are given in Figure 4, where the parameters, u1, L and λ are given as a function of the distance of the grid, x; these findings are compared with other experimental and theoretical data. The results of the settling study for different spherical particles settling in different turbulent media are given in form of a CT vs RE relationship; see Figure 6. It is to be noted that the drag coefficient is in some cases superior and in others inferior when compared with the non-turbulent data. For all RE studied, it was found that drag coefficients diminish if the turbulent velocity, u1, increases and simultaneously the macroscale, L, decreases. Around a RE = 2000, drag coefficients show a distinguishable "hump", whereby they may fall above the non-turbulent data. The study's conclusion is that the present experimental data are best represented with the dimensional parameter, u1/L, given in Fig. 9.

DOI: https://doi.org/10.1080/00221688209499469

Year: 1982