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Particle and particle-fluid flows are ubiquitous in nature and in industrial processes, yet theirmechanics are not well understood. Several factors contribute to the lack of understanding, such asthe complex nature of particle interactions (e.g., friction in dry systems, hydrodynamic interactionsin suspensions), the complexity of the microstructure, and the dependence of the macroscopicbehavior on the nature of forcing. Though considerable progress has been made in the recentdecades, many open questions remain. When the forces exerted by the fluid on the grains are muchsmaller than the contact forces, the systems are referred to as dry granular flows. Many instancesof particulate flows fall in this category, and historically dry granular flows have been studied inthe two extreme regimes of slow (quasistatic) flow and rapid flow, which are discussed at greaterlength in Sec. III. Only recently have researchers begun to investigate the vast “intermediate”regime that lies between slow and rapid flows. The fluid exerts large enough forces on the particleseither when its velocity relative to the particles is large (typically in gas-particle flows such asin fluidized beds and pneumatic conveying), or when its viscosity is sufficiently high (typicallyin liquid-particle systems, as in slurries, paints, and inks) – these two regimes are conceptuallyimportant and have been well studied, but situations intermediate between them are also foundin nature and industry. The description of gas-particle flows has been largely phenomenological,wherein reasonable forms are chosen for the constitutive models for gas-phase turbulence, inter-particle and particle-gas interactions; nevertheless, these models have proved quite useful in derivingqualitative, and sometimes quantitative, information on problems such as bubble dynamics, mixingand convection currents in fluidized beds.Yet, a clearer understanding of the interaction of suspendedparticles with large and small turbulent structures in the carrier fluid is of great importance in manyindustrial and environmental processes. In the opposite regime of liquid-particle flows, a large bodyof literature over the past five decades has concentrated on the regime where particle and fluid inertiaare either precisely zero, or small. Despite its apparent simplicity, a suspension of rigid particlesin a Newtonian fluid exhibits several interesting complexities, such as non-Newtonian rheology,spontaneous segregation of particles, etc. Though much progress has been made on understanding these problems through experimental, analytical and computational tools, much still remains to bedone to understand suspension rheology and dynamics.Aproposalwasmade to the InternationalUnion of Theoretical andAppliedMechanics (IUTAM)for organizing a symposium to bring together experts in this broad area, to make an assessment ofthe state of current research and suggest directions for future work. A second and equally importantmotivation was to bring young scholars and graduate students in contact with the experts in thefield, in an atmosphere that is conducive to informal interaction and exchange of ideas. The IUTAMapproved the proposal, and nominated a scientific committee.1This symposium follows a seriesof conferences on particle and particle-fluid flows, several held under the aegis of the IUTAM.Funding for the symposium was provided by the IUTAM, the National Science Foundation, USA,the Department of Science and Technology, India, Tata Consultancy Services, Anton Paar GmbH,and Accurion GmbH.The symposium focused on three distinct but complementary topics:Flow of granular materials,Dynamics and rheology of fluid-particle suspensions,Kinematics and statistics of living suspensions.Forty four presentations were made in all, which were divided thematically over the five daysof the symposium. The first speaker for each theme gave an overview of recent developments inthe field and summarized the open questions, before proceeding to deliver his or her presentation.Sections II–IV describe the topics that were discussed, and describe briefly the presentations of theparticipants (not necessarily in the order of presentation). Some of the presentations appear as papersfollowing this report in this Special Topic section of Physics of Fluids. This report and the papers inthe Special Topic section constitute the proceedings of the symposium. The complete program andbook of abstracts for the symposium has been deposited as supplementary information.2
Author(s): Nott PR, Davis RH, Reeks M, Saintillan D, Sundaresan S
Publication type: Article
Publication status: Published
Journal: Physics of Fluids
Year: 2013
Volume: 25
Issue: 7
Print publication date: 18/07/2013
ISSN (print): 1070-6631
ISSN (electronic): 1089-7666
Publisher: American Institute of Physics
URL: http://dx.doi.org/10.1063/1.4812639
DOI: 10.1063/1.4812639
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