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Über dieses Buch

This book studies the dynamics of 2D objects moving through turbulent fluids. It examines the decay of turbulence over extended time scales, and compares the dynamics of non-spherical particles moving through still and turbulent fluids.

The book begins with an introduction to the project, its aims, and its relevance for industrial applications. It then discusses the movement of planar particles in quiescent fluid, and presents the numerous methodologies used to measure it. The book also presents a detailed analysis of the falling style of irregular particles, which makes it possible to estimate particle trajectory and wake morphology based on frontal geometry. In turn, the book provides the results of an analysis of physically constrained decaying turbulence in a laboratory setting. These results suggest that large-scale cut-off in numerical simulations can result in severe bias in the computed turbulent kinetic energy for long waiting times.

Combining the main text with a wealth of figures and sketches throughout, the book offers an accessible guide for all engineering students with a basic grasp of fluid mechanics, while the key findings will also be of interest to senior researchers.



Chapter 1. Introduction

The industrial aim associated to this project is to improve the efficiency of a novel device that separates glass and plastic particles from a co-mingled waste product coming from Material Recovery Facilities (MRF). This waste product is mainly composed of glass, plastic, paper-based materials and metals. However, most of the metals are removed from the raw product before this enters the separator, whereas paper and other cellulose-based materials are suspended in water. Thus, the main task of this device is to separate plastics that are lighter and heavier than water from glass; and the later water treatment that permits to filter the pulp suspended in it.
Luis Blay Esteban

Chapter 2. Planar Particles in Quiescent Fluid

The aim of this chapter is to investigate experimentally the effect of the frontal geometry on the settling dynamics of planar particles in quiescent flow. The question “What if the disc has a wavy edge?” formulated in Moffat (J Fluid Mech 720:1–4, 2013) is extended here not only to sinusoidal edge particles but to sharp edge polygons and three studies are combined to tackle this question. First, particle tracking experiments of disk-like particles with the perimeter described by sinusoidal functions are performed. We differentiate trajectories according to the degree of out of plane motion and obtain a drag correlation function that depends on the particle geometry. Second, trajectories of N-sided polygons with the same material properties and frontal area but different number of sides are also investigated by particle tracking experiments and a simple pendulum model is found to represent accurately the descent motion of these particles once the mean descent velocity is known. Finally, we perform measurements of the instantaneous three-dimensional velocity field on the wake of several of these polygons. We observe severe differences in the shedding mechanisms and these are related to the descent style of the particles.
Luis Blay Esteban

Chapter 3. Facility for Turbulence Generation

This chapter presents an experimental facility designed to generate and control turbulence in a laboratory. This consists of a modified version of the random jet array (RJA) proposed in Bellani and Variano (Exp Fluids 55:1646–1666, 2013, [1]) that allows us to generate homogeneous and anisotropic turbulence. Moreover, this zero-mean flow facility can be used to investigate the temporal decay of turbulence without invoking Taylor’s hypothesis. Thus, the aim of this chapter is twofold: first present the facility designed and second investigate the evolution of anisotropic turbulence over time and evaluate the spatial confinement effect. Once these two questions are answered we will have the tools to examine how different turbulent flows modify the descent style of large inertial particles; and this, at the same time will give us some insight into the particle behaviour inside Aquavitrum’s tank. This chapter is structured as follows; in Sect. 3.1 we introduce zero-mean flow facilities used to generate turbulence and we detail experimental and numerical results on the decay of turbulence with and without confinement effects, in Sect. 3.2 we present the experimental setup and the measurement technique, Sects. 3.3 and 3.4 show the results for stationary and decay turbulence, respectively, and we conclude in Sect. 3.5.
Luis Blay Esteban

Chapter 4. Disks Falling Under Background Turbulence

Despite the ubiquity of turbulent flows with non-spherical particles, it has been only relatively recently that experiments have been developed to measure the motion and orientation of individual particles in a turbulent environment. Early experimental work was focused on particle motion in complex cases relevant to specific applications; Bernstein and Shapiro [1] measured the orientation of glass fibre cylindrical particles suspended in a laminar and turbulent shear flow in a water tunnel and Noel and Sassen [2] among others focused on ice crystals in clouds. Fibre-like particles have been extensively investigated during the last decades due to their direct application to several industrial sectors such as the papermaking industry, as reviewed in Voth and Soldati [3]. However, most of the research done on these flows is focused on the orientation, preferential concentration and alignment of the fibres with the turbulent flow while these are suspended and not on the turbulence effect on the particle settling rate. Also, the severe differences in the dynamics of the fibres compared with the finite-size inertial disks investigated here represents a clear differentiator between these systems.
Luis Blay Esteban

Chapter 5. Conclusions

In this study, the descent motion of planar particles in quiescent flow and under turbulence effects has been investigated. Experiments were conducted to explore the motion of irregular planar particles in quiescent flow always with a equivalent disk (same frontal area) as a baseline. Then, a zero-mean flow turbulence facility was designed and built; and the flow in the central region of the facility was characterized non only for the statistically stationary case but for free decaying turbulence. Last, the descent of inertial disks under zero-mean flow turbulence was investigated. The study was conducted as an experimental work using particle tracking, volumetric velocimetry (V3V) and planar PIV. The outcomes of the study will be summarised below.
Luis Blay Esteban


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