Numerical investigation of quasi-static bubble growth and detachment from submerged orifices in isothermal liquid pools: The effect of varying fluid properties and gravity levels

The present investigation, identifies the exact quantitative effects of fundamental parameters, on the detachment characteristics of isolated bubbles, emanating quasi-statically from submerged orifices into isothermal liquid pools. For this purpose, a Volume of Fluid (VOF) based interface capturing approach is further improved, for the conduction of axisymmetric and 3D numerical experiments on adiabatic bubble growth dynamics. The predictions of the model, are quantitatively validated against literature available experimental data, showing excellent agreement. Two series of numerical experiments are performed, quantitatively exploring the parametric effects of the liquid phase properties in five different gravity levels, and the effect of the gravity vector direction inclination angle, respectively. It is found that the bubble detachment characteristics, are more sensitive in the variation of the surface tension, liquid phase density and gravity, while the effect of liquid phase dynamic viscosity is generally minimal. From dimensionless analysis, two correlations are derived, which for the examined range of Eötvos numbers, are able to predict the equivalent bubble detachment diameter and the bubble detachment time, respectively. It is also found that the bubble detachment characteristics, reduce significantly as the gravity vector direction gradually deviates from being parallel to the bubble injection orifice, following a non-linear decrease

Effet de l'angle de flèche sur le bruit à large bande de ventilateur

Cette étude vise à comprendre la mécanique de réduction de bruit afin de mitiger le bruit large bande en utilisant l’angle de flèche tout en préservant le rendement aérodynamique. Nous avons choisi des modèles et outils de calculs afin de comprendre le comportement aérodynamique ainsi que le bruit généré par l’angle de flèche. En premier lieu, une simulation Reynolds Averaged Navier Stokes (RANS) est utilisée afin d’évaluer le champ d’écoulement. Ensuite, une méthode Lattice Boltzmann (LBM) haute-fidélité est utilisée afin de prédire la radiation sonore. LBM nous permet de déterminer la source des bruits combinés. Finalement, afin de séparer le bruit large bande généré par les turbulences, nous avons adapté le modèle d’Amiet's leading-edge afin de représenter l’angle de flèche d’un ventilateur axial. Nos résultats indiquent que le dévers de pale avant surpasse le dévers de pale arrière pour la région décrochage, la radiation sonore et la consommation énergétique lorsque les performances aérodynamique est restaurée.Le bruit produit par le ventilateur de radiateur devient une préoccupation croissante. En effet, les véhicules électriques modernes ne produisent pas le bruit engendré par les groupes motopropulseurs et moteurs traditionnels. Fondé sur une revue de littérature, nous avons classé les différentes sources de bruit ainsi que leur contribution sur le spectre acoustique. Les concepts de dévers de pale avant et arrière ont démontré un potentiel avantage de réduction de bruit large bande aux détriments du rendement aérodynamique. Par conséquent, cette approche est très peu utilisée dans l'industrie. Cette étude vise à comprendre la mécanique de réduction de bruit afin de mitiger le bruit large bande en utilisant l'angle de flèche tout en préservant le rendement aérodynamique. Nous avons choisi des modèles et outils de calculs afin de comprendre le comportement aérodynamique ainsi que le bruit généré par l'angle de flèche. En premier lieu, une simulation Reynolds Averaged Navier Stokes (RANS) est utilisée afin d'évaluer le champ d'écoulement. Ensuite, une méthode Lattice Boltzmann (LBM) haute-fidélité est utilisée afin de prédire la radiation sonore. LBM nous permet de déterminer la source des bruits combinés. Finalement, afin de séparer le bruit large bande généré par les turbulences, nous avons adapté le modèle d'Amiet's leading edge afin de représenter l'angle de flèche d'un ventilateur axial. Nos résultats indiquent que le dévers de pale avant surpasse le dévers de pale arrière pour la région décrochage, la radiation sonore et la consommation énergétique lorsque les performances aérodynamique est restaurée. Nous recommandons le dévers de pale avant afin de réduire le bruit de large bande émis par le ventilateur du radiateur. Cependant, des recherches additionnelles seront nécessaires afin d'évaluer le bruit tonal. Ces recherches pourront renforcer l'utilisation de l'angle de flèche dans la conception de pales.Abstract : The radiator fan noise is becoming a growing concern since other noise sources radiated from traditional powertrains and combustion engines are omitted in modern electric vehicles. Based on a literature review, we classified the noise sources and their contribution in noise spectra. The forward sweep and backward sweep showed a strong potential in broadband noise reduction but at the cost of loss in aerodynamic efficiency. Hence, this skepticism restrained from its wide usage in fan design. Therefore, this study aims at understanding the noise reduction mechanism so that to mitigate broadband noise using blade sweep by preserving its aerodynamic performance. The various computational tools are used to investigate the aerodynamic behavior and its associated noise in swept blades. First, an industry-friendly steady Reynolds Averaged Navier Stokes (RANS) simulation technique is assessed to investigate the flow field and later a high-fidelity, unsteady Lattice Boltzmann method (LBM) is evaluated to predict the noise radiation. LBM provides the combined knowledge of all noise sources. So, finally, to segregate broadband noise generated due to turbulence interaction, we adapted Amiet's leading-edge noise prediction tool to the swept blade of an axial fan. The results indicate that forward sweep has improved pressure rise by almost 25% than backward sweep and unswept blade when designed for similar loadings. In addition, the forward sweep has reduced noise levels by 12 dB than unswept blade. We recommend using a forward sweep to reduce broadband noise emitted by the radiator fan based on our findings. However, further research is needed to investigate tonal noise that could strengthen the usage of sweep in blade design

Microfluidics and Nanofluidics Handbook

The Microfluidics and Nanofluidics Handbook: Two-Volume Set comprehensively captures the cross-disciplinary breadth of the fields of micro- and nanofluidics, which encompass the biological sciences, chemistry, physics and engineering applications. To fill the knowledge gap between engineering and the basic sciences, the editors pulled together key individuals, well known in their respective areas, to author chapters that help graduate students, scientists, and practicing engineers understand the overall area of microfluidics and nanofluidics. Topics covered include Finite Volume Method for Numerical Simulation Lattice Boltzmann Method and Its Applications in Microfluidics Microparticle and Nanoparticle Manipulation Methane Solubility Enhancement in Water Confined to Nanoscale Pores Volume Two: Fabrication, Implementation, and Applications focuses on topics related to experimental and numerical methods. It also covers fabrication and applications in a variety of areas, from aerospace to biological systems. Reflecting the inherent nature of microfluidics and nanofluidics, the book includes as much interdisciplinary knowledge as possible. It provides the fundamental science background for newcomers and advanced techniques and concepts for experienced researchers and professionals

Theory of charge-spin conversion phenomena in two-dimensional electronic systems: from graphene heterostructures to Rashba-coupled interfaces

Using the electron’s spin in addition to its charge represents a promising avenue for future solid-state devices. The potential of this field of research, called spintronics, has been propelled by the advent of graphene and related atomically-thin materials, which have enabled unprecedented electric control over spin dynamics and spin-charge conversion effects in layer-by-layer systems. This thesis aims to contribute towards a broader understanding of spin-dependent phenomena in two spintronic platforms of much current interest; honeycomb layers and interfaces hosting two-dimensional electron gases and topologically protected states. These systems are characterized by rich symmetry-breaking spin-orbit coupling effects, which render theoretical descriptions of electronic structure and spin transport highly nontrivial. Therefore, this work aims to develop a unified microscopic treatment that captures, on equal footing, disorder-limited spin dynamics and disorder-enhanced spin- charge conversion effects, two complementary phenomena at the heart of modern spin- tronics. On the first front, we put forward a diagrammatic method that allows the derivation of space and time-dependent kinetic equations for generic 2D electronic systems. Ap- plied to adatom-decorated graphene, it uncovers the interband spin-orbit scattering at the origin of sizable current-induced spin currents. Secondly, we study the possibility of acquiring twist-angle control over spin-charge conversion effects in novel graphene-based heterostructures, where a rotation angle between adjacent layers strongly modifies the spin texture of electronic bands, thus opening the possibility of realizing unconven- tional spin galvanic effects. Our formulation is also applied to studying spin-orbit torques in ferromagnet bilayers. We find that skew scattering from ubiquitous short- range impurities can produce significant damping-like torques, allowing for all-electrical magnetization switching of a nearby micromagnet. Our work highlights the crucial role played by electronic structure modifications at interfaces in the generation of spin-dependent forces experienced by transport electrons and the necessity for an adequate treatment of impurity scattering for describing the behaviour of realistic spintronic materials

Immersed boundary simulations and tools for studying insect flight and other applications

All organisms must deal with fluid transport and interaction, whether it be internal, such as lungs moving air for the extraction of oxygen, or external, such as the expansion and contraction of a jellyfish bell for locomotion. Most organisms are highly deformable and their elastic deformations can be used to move fluid, move through fluid, and resist fluid forces. A particularly effective numerical method for biological fluid-structure interaction simulations is the immersed boundary (IB) method. An important feature of this method is that the fluid is discretized separately from the boundary interface, meaning that the two meshes do not need to conform with each other. This thesis covers the development of a new software tool for the semi-automated creation of finite difference meshes of complex 2D geometries for use with immersed boundary solvers IB2d and IBAMR, alongside two examples of locomotion - the flight of tiny insects and the metachronal paddling of brine shrimp. As mentioned, an advantage of the IB method is that complex geometries, e.g., internal or external morphology, can easily be handled without the need to generate matching grids for both the fluid and the structure. Consequently, the difficulty of modeling the structure lies often in discretizing the boundary of the complex geometry (morphology). Both commercial and open source mesh generators for finite element methods have long been established; however, the traditional immersed boundary method is based on a finite difference discretization of the structure. In chapter \ref{chap:meshmerizeme}, I present a software library called MeshmerizeMe for obtaining finite difference discretizations of boundaries for direct use in the 2D immersed boundary method. This library provides tools for extracting such boundaries as discrete mesh points from digital images. Several examples of how the method can be applied are given to demonstrate the effectiveness of the software, including passing flow through the veins of insect wings, within lymphatic capillaries, and around starfish using open-source immersed boundary software. As an example of insect flight, I present a 3D model of clap and fling. Of the smallest insects filmed in flight, most if not all clap their wings together at the end of the upstroke and fling them apart at the beginning of the downstroke. This motion increases the strength of the leading edge vortices generated during the downstroke and augments the lift. At the Reynolds numbers ($Re$) relevant to flight in these insects (roughly $4<Re<40$), the drag produced during the fling is substantial, although this can be reduced through the presence of wing bristles, chordwise wing flexibility, and more complex wingbeat kinematics. It is not clear how flexibility in the spanwise direction of the wings can alter the lift and drag generated. In chapter \ref{chap:clapfling}, a hybrid version of the immersed boundary method with finite elements is used to simulate a 3D idealized clap and fling motion across a range of wing flexibilities. I find that spanwise flexibility, in addition to three-dimensional spanwise flow, can reduce the drag forces produced during the fling while maintaining lift, especially at lower $Re$. While the drag required to fling 2D wings apart may be more than an order of magnitude higher than the force required to translate the wings, this effect is significantly reduced in 3D. Similar to previous studies, dimensionless drag increases dramatically for $Re<20$, and only moderate increases in lift are observed. Both lift and drag decrease with increasing wing flexibility, but below some threshold, lift decreases much faster. This study highlights the importance of flexibility in both the chordwise and spanwise directions for low $Re$ insect flight. The results also suggest that there is a large aerodynamic cost if insect wings are too flexible. My second application of locomotion pertains to a 2D model of swimming, specifically the method known as metachronal paddling. This method is used by a variety of organisms to propel themselves through a fluid. This mode of swimming is characterized by an array of appendages that beat out of phase, such as the swimmerets used by long-tailed crustaceans like crayfish and lobster. This form of locomotion is typically observed over a range of Reynolds numbers greater than 1 where the flow is dominated by inertia. The majority of experimental, modeling, and numerical work on metachronal paddling has been conducted on the higher Reynolds number regime (order 100). In this chapter, a simplified numerical model of one of the smaller metachronal swimmers, the brine shrimp, is constructed. Brine shrimp are particularly interesting since they swim at Reynolds numbers on the order of 10 and sprout additional paddling appendages as they grow. The immersed boundary method is used to numerically solve the fluid-structure interaction problem of multiple rigid paddles undergoing cycles of power and return strokes with a constant phase difference and spacing that are based on brine shrimp parameters. Using a phase difference of 8\%, the volumetric flux and efficiency per paddle as a function of the Reynolds number and the spacing between legs is quantified. I find that the time to reach periodic steady state for adult brine shrimp is large ($\approx 150$ stroke cycles) and decreases with decreasing Reynolds number. Both efficiency and average flux increase with Reynolds number. In terms of leg spacing, the average flux decreases with increased spacing while the efficiency is maximized for intermediate leg spacing.Doctor of Philosoph

A study of the dynamics and rheology of passive and active suspensions of particles with various geometries

Suspensions of particles in fluids are everywhere in our life, such as paints, pharmacies, food, etc. Suspensions can exhibit properties that common fluids do not possess. For example, the paint needs to flow well when brushing so that it can be smeared on the wall, which is aided by the shear-thinning of the fluid. However, when brushing stops, paint needs to stay still on the wall, which is aided by the yield-stress of the paint. These types of behavior depend on the dynamics and microstructures of the suspensions. Suspensions of particles can serve as precursors of composite materials, for example, a composite can be created by curing a suspension of particles in a monomer solution. In such case, the properties of the composite can be affected by the dynamics of the fluid. Investigating the dynamics of suspensions of particles can be crucial to the manufacture of composite materials. This study covers theoretical, computational, and experimental studies of suspensions of particles in various aspects, such as suspensions of spherical and aspherical particles, suspensions with or without external fields, and suspensions in Newtonian and non-Newtonian fluids. The theoretical and computational study focuses on a fundamental investigation of the dynamics of the suspending particles. Under a magnetic field, magnetic disks can be aligned by a magnetic field. An analytic solution that describes the motion of a single magnetic disk under a rotating field is derived in this study, and it has shown good comparison with experimental data. When multiple particles are present in the fluid, the particles interact with each other hydrodynamically and magnetically if a magnetic field is applied. Under the influence of the magnetic field, the microstructures of the material can be altered. The dynamic behavior depends on hydrodynamic interactions. I discuss the hydrodynamic and magnetic interactions from a fundamental point of view, and I implement a computational method called Stokesian dynamics to simulate such systems. Furthermore, I also discuss a way of simulating aspherical suspensions that is based on the spherical suspensions. The experimental study focuses on the characterization of complex fluids by suspending microparticles as the probes that can measure the local properties of fluids, and the method is called microrheology. The complex fluids that are characterized in this study serve as an inexpensive substitute of the sputum of cystic fibrosis (CF) patients. The goal of this part of the study is to explore an efficient drug-delivery vehicle that can transport through the mucus of CF patients. The formula of the substituting fluids that are proposed by our lab has shown similar rheological properties with the sputum from CF patients in the macroscopic lengthscale. I also characterized the fluids in the microscopic lengthscale and I have seen differences between the macroscopic and microscopic properties. I deduce that the differences arise from the heterogeneity of the fluids, which cannot be well detected in the macroscopic method. Finally, I combine the knowledge that we obtain from the theoretical study with the technique that we utilize in the experimental study to obtain a proof-of-concept study. We have successfully suspended microdisks in a yield-stress fluid so that the microdisks can be aligned while constrained in the elastic cages of the fluid. The yield-stress is characterized by a microrheological technique, and we apply the scalings that we have derived previously to control the parameters to achieve the goal of aligning microdisks while suppressing the translations of microdisks

Proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress

Published proceedings of the 2018 Canadian Society for Mechanical Engineering (CSME) International Congress, hosted by York University, 27-30 May 2018

New Directions for Contact Integrators

Contact integrators are a family of geometric numerical schemes which guarantee the conservation of the contact structure. In this work we review the construction of both the variational and Hamiltonian versions of these methods. We illustrate some of the advantages of geometric integration in the dissipative setting by focusing on models inspired by recent studies in celestial mechanics and cosmology.Comment: To appear as Chapter 24 in GSI 2021, Springer LNCS 1282