10 research outputs found
Nonlinear JOREK simulations of the Greenwald density limit with a thermo-resistive radiation model
Get PDFData underlying the publication: Numerical study of a pair of spheres in an oscillating box filled with viscous fluid
No full textThis data set contains all the data to reproduce the results presented in van Overveld, T. J., Shajahan, M. T., Breugem, W. P., Clercx, H. J., & Duran-Matute, M. (2022). Numerical study of a pair of spheres in an oscillating box filled with viscous fluid. Physical Review Fluids, 7(1), 014308. All data processing is done in Jupyter-Lab. FigureX.ipynb is used the preprocessed data and functions to generate Figure X from the original paper
Numerical study of a pair of spheres in an oscillating box filled with viscous fluid
Get PDFWhen two spherical particles submerged in a viscous fluid are subjected to an oscillatory flow, they align themselves perpendicular to the direction of the flow leaving a small gap between them. The formation of this compact structure is attributed to a nonzero residual flow known as steady streaming. We have performed direct numerical simulations of a fully resolved, oscillating flow in which the pair of particles is modeled using an immersed boundary method. Our simulations show that the particles oscillate both parallel and perpendicular to the oscillating flow in elongated figure-8 trajectories. In absence of bottom friction, the mean gap between the particles depends only on the normalized Stokes boundary layer thickness δ∗, and on the normalized, streamwise excursion length of the particles relative to the fluid Ar∗ (equivalent to the Keulegan-Carpenter number). For Ar∗≲1, viscous effects dominate and the mean particle separation only depends on δ∗. For larger Ar∗ values, advection becomes important and the gap widens. Overall, the normalized mean gap between the particles scales as L∗≈3.0δ∗1.5+0.03Ar∗3, which also agrees well with previous experimental results. The two regimes are also observed in the magnitude of the oscillations of the gap perpendicular to the flow, which increases in the viscous regime and decreases in the advective regime. When bottom friction is considered, particle rotation increases and the gap widens. Our results stress the importance of simulating the particle motion with all its degrees of freedom to accurately model the system and reproduce experimental results. The insights of the particle pairs provide an important step towards understanding denser and more complex systems. Multi Phase System
Effect of the Stokes boundary layer on the dynamics of particle pairs in an oscillatory flow
Get PDFThe alignment of a pair of spherical particles perpendicular to a horizontally oscillating flow is attributed to a non-zero residual flow, known as steady streaming. This phenomenon is the basis of complex patterns in denser systems, such as particle chains and the initial stages of rolling-grain ripples. Previous studies on such self-organization processes used two distinct systems: an oscillating box filled with viscous fluid and an oscillating channel flow, where the fluid oscillates relative to the bottom boundary. In this paper, we show that particle pair dynamics in these two systems are fundamentally different, due to the presence of a Stokes boundary layer above the bottom in the oscillating channel flow. The results are obtained from direct numerical simulations in which the dynamics of a pair of particles are simulated using an immersed boundary method. The oscillating box and the oscillating channel flow are only equivalent in a limited region of the parameter space, where both the normalized Stokes boundary layer thickness and the normalized relative particle excursion length are small. Overall, the particle dynamics in the oscillating channel flow, compared to the oscillating box, are governed by an additional dimensionless parameter, that is, the particle–fluid density ratio
Data underlying the publication: Pattern formation of spherical particles in an oscillating flow
No full textThis data set contains all the data to reproduce the results presented in the manuscript titled 'Pattern formation of spherical particles in an oscillating flow'. All data processing is done in Jupyter-Lab and Paraview. FigureX.ipynb uses the preprocessed data and functions to generate Figure X from the original manuscript. See the file README.txt for more information about data structure and processing
Incipient motion of a single particle on a regular substrate in an oscillatory flow
No full textWe investigate and model the initiation of motion of a single particle on a structured substrate within an oscillatory boundary layer flow, following a mechanistic approach. By deterministically relating forces and torques acting on the particle to the instantaneous ambient flow, the effects of flow unsteadiness are captured, revealing rich particle dynamics. Laboratory experiments in an oscillatory flow tunnel characterise the initiation and early stages of motion, with particle imaging velocimetry measurements yielding the flow conditions at the motion threshold. The experiments validate and complement results from particle-resolved direct numerical simulations, combining an immersed boundary method with a discrete element method that incorporates a static friction contact model. Within the parameter range just above the motion threshold, the mobile particle rolls without sliding over the substrate, indicating that motion initiation is governed by an unbalanced torque rather than a force. Both experimental and numerical results show excellent agreement with an analytical torque balance including hydrodynamic torque derived from the theoretical Stokes velocity profile, and contributions of lift, added mass and externally imposed pressure gradient. In addition to static and rolling particle states, we identify a wiggling regime where the particle moves but does not leave its original pocket. Our deterministic approach enables prediction of the phase within the oscillation cycle at which the particle starts moving, without relying on empirical threshold estimates, and can be extended to a wide range of flow and substrate conditions, as long as turbulence is absent and interactions with other mobile particles are negligible
Pattern formation of spherical particles in an oscillating flow
Get PDFWe study the self-organization of spherical particles in an oscillating flow through experiments inside an oscillating box. The interactions between the particles and the time-averaged (steady streaming) flow lead to the formation of either one-particle-thick chains or multiple-particle-wide bands, depending on the oscillatory conditions. Both the chains and the bands are oriented perpendicular to the direction of oscillation with a regular spacing between them. For all our experiments, this spacing is only a function of the relative particle-fluid excursion length normalized by the particle diameter, Ar/D, implying that it is an intrinsic quantity that is established only by the hydrodynamics. In contrast, the width of the bands depends on both Ar/D and the confinement, characterized by the particle coverage fraction ϕ. Using the relation for the chain spacing, we accurately predict the transition from one-particle-thick chains to wider bands as a function of ϕ and Ar/D. Our experimental results are complemented with numerical simulations in which the flow around the particles is fully resolved. These simulations show that the regular chain spacing arises from the balance between long-range attractive and short-range repulsive hydrodynamic interactions, caused by the vortices in the steady streaming flow. We further show that these vortices induce an additional attractive interaction at very short range when Ar/D≳0.7, which stabilizes the multiple-particle-wide bands. Finally, we give a comprehensive overview of the parameter space where we illustrate the different regions using our experimental data
From hydrodynamics to dipolar colloids: Modeling complex interactions and self-organization with generalized particles
Get PDFThe self-organization of clusters of particles is a fundamental phenomenon across various physical systems, including hydrodynamic and colloidal systems. One example is that of dense spherical particles submerged in a viscous fluid and subjected to horizontal oscillations. The interaction of the particles with the oscillating flow leads to the formation of one-particle-thick chains or multiple-particle-wide bands, both oriented perpendicular to the oscillation direction. In this study, we model the hydrodynamic interactions between such particles and parallel chains using simplified potentials. We first focus on the hydrodynamic interactions between chains, which we characterize using data from fully resolved numerical simulations. Based on these interactions, we propose a simplified model potential, called the potential, which combines the representative hydrodynamic interactions: short-range attraction, mid-range repulsion, and long-range attraction. Through one-dimensional Monte Carlo simulations, we successfully replicate the characteristic patterns observed in hydrodynamic experiments and draw the phase diagram for the model potential. We further extend our analysis to two-dimensional systems, introducing a model potential that accounts for both chain formation and -like chain interactions. This potential is based on a system with colloidal particles at an interface, where chain formation is driven by an external electric field that induces a dipole moment parallel to the interface in each particle. The capillary force contributes the long-range attraction. Starting with parallel chains, the patterns in the two-dimensional Monte Carlo simulations of this colloidal system are similar to those observed in the hydrodynamic experiments. However, we identify that nonlinear interactions are important for some distinct steps in the chain formation. Still, the model potentials help clarify the dynamic behavior of the particles and chains due to the complex interactions encountered in both hydrodynamic and colloidal systems, drawing parallels between them
Data underlying the manuscript: The effect of the Stokes boundary layer on the dynamics of particle pairs in an oscillatory flow
No full textThis data set contains all the data to reproduce the results presented in the manuscript titled 'The effect of the Stokes boundary layer on the dynamics of particle pairs in an oscillatory flow'. All data processing is done in Jupyter-Lab. FigureX.ipynb uses the preprocessed data and functions to generate Figure X from the original manuscript. See the file README.txt for more information about data structure and processing
Dataset underlying the publication: From hydrodynamics to dipolar colloids: modeling complex interactions and self-organization with generalized potentials
No full textThis data set contains all the data to reproduce the results presented in the manuscript titled 'From hydrodynamics to dipolar colloids: modeling complex interactions and self-organization with generalized potentials'. All data processing is done in Jupyter-Lab. FigureX.ipynb uses the preprocessed data and functions to generate Figure X from the original manuscript. See the file README.txt for more information about data structure and processing
