| Mon September 19th 2016 16:30 – 17:00 ZH286 | Seminar | Columnar structure formation of a dilute suspension of settling spherical particles in a quiescent fluid Sander Huisman |
Details:In the present work the settling of heavy spherical particles in a column of quiescent fluid is investigated. The performed experiments cover a range of Galileo numbers 100 <= Ga <= 300 for a fixed density ratio of ρ_p/ρ_f = 2.4, where Ga = u_g D/ν can be thought of as a Reynolds number based on the gravitational velocity. In this regime the particles are known to show a variety of motions. Simulations have shown that the wake undergoes several transitions for increasing Ga resulting in particle motions that are: vertical, oblique, oblique oscillating, and finally chaotic. Not only does this change the trajectory of single, isolated, settling particles, but it also changes the dynamics of a swarm of particles as collective effects become important even for dilute suspensions, with volume fraction Φ_V = Ο(10^-3) (M. Uhlmann and T. Doychev, J. Fluid Mech. 752, 310 (2014)), which are investigated in this work. Multi-camera recordings of settling particles are recorded and tracked over time in 3 dimensions. A variety of analysis are performed and show a strong clustering behavior. The distribution of the cell areas of the Voronoï tessellation in the horizontal plane are compared to that of a random distribution of particles and shows clear clustering. Moreover, a negative correlation was found between the Voronoï area and the particle velocity; clustered particles fall faster. In addition, the angle between two adjacent particles and the vertical is calculated and compared to a homogeneous distribution of particles, clear evidence of vertical alignment of particles is found. The experimental findings are compared to simulations. | ||
