应航天航空学院Marie-Jean Thoraval教授邀请，荷兰屯特大学Sander Huisman教授将来访我校并作学术报告。

报告人：Sander Huisman教授

时间：2017年10月10日上午9:00-11:30

地点：航天航空学院教一楼第三会议室

报告题目：Settling of spherical particles in a quiescent fluid

报告摘要：

In this talk we discuss the settling of heavy spherical particles in a column of quiescent fluid. 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 u_g=(|ρ_p/ρ_f - 1| Dg)^(1/2). In this regime the particles are known (M. Jenny, J. Dusek and G. Bouchet, J. Fluid Mech. 508, 201 (2004)) 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.

报告人简介：

Dr. Sander Huisman obtained his PhD in 2014 in the Physics of Fluids group at the University of Twente in the Netherlands under supervision of Chao Sun and Detlef Lohse. Huisman did his postdoctoral research at the École Normale Supérieure in Lyon on particles tracking in quiescent and turbulent flows. He is currently an assistant professor at the University of Twente on turbulent flows with heat and mass transfer. He has published in journals such as Nature Communications, PRL, PRE, PRF, JFM, and Rev. Sci. Instruments. He is interested in turbulent flows: Rayleigh-Bénard, Taylor-Couette, von Kármán, channel, pipe flows, et cetera. Furthermore, he has a keen interest in applying measurements techniques, like laser Doppler anemometry, particle tracking velocimetry, and high-speed particle image velocimetry, to the aforementioned geometries. At the University of Twente and the École Normale Supérieure he acquired a broad knowledge in fluid dynamics; ranging from turbulent flows to granular flows, both theoretically and experimentally. Also two-phase flows are of his interest; at the Institut de Méchanique des Fluides de Toulouse he looked at the coalescence of bubbles in a 2D confinement.