AuthorsThoroddsen, Sigurdur T
KAUST DepartmentHigh-Speed Fluids Imaging Laboratory
Mechanical Engineering Program
Physical Science and Engineering (PSE) Division
Online Publication Date2020-01-28
Print Publication Date2020-01-01
Embargo End Date2021-01-28
Permanent link to this recordhttp://hdl.handle.net/10754/661331
MetadataShow full item record
AbstractWe investigate the dynamics of a drop containing a single solid particle impacting on a solid surface. The particle rebounds through the drop during impact and can separate from the deposited liquid above an impact velocity threshold. We show that this threshold can be predicted by a simple energy balance. Moreover, we discover a new type of liquid jetting ejected above the particle faster than the impact velocity. We demonstrate that this jetting is due to the focusing effect of the liquid on the solid substrate below the rebounding particle. Although the wetting properties of the particle have a minor effect on the separation threshold, they play a key role in the liquid jetting by affecting the immersion depth of the particle at the time of impact.
CitationThoroddsen, S. T., & Thoraval, M.-J. (2020). Jetting from an impacting drop containing a particle. Physics of Fluids, 32(1), 011704. doi:10.1063/1.5139534
JournalPhysics of Fluids
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Showing items related by title, author, creator and subject.
Drop impact into a deep pool: Vortex shedding and jet formationAgbaglah, Gilou; Thoraval, Marie-Jean; Thoroddsen, Sigurdur T; Zhang, Li V.; Fezzaa, Kamel; Deegan, Robert D. (Journal of Fluid Mechanics, Cambridge University Press (CUP), 2015-01-02) [Article]One of the simplest splashing scenarios results from the impact of a single drop on a deep pool. The traditional understanding of this process is that the impact generates an axisymmetric sheet-like jet that later breaks up into secondary droplets. Recently it was shown that even this simplest of scenarios is more complicated than expected because multiple jets can be generated from a single impact event and there are transitions in the multiplicity of jets as the experimental parameters are varied. Here, we use experiments and numerical simulations of a single drop impacting on a deep pool to examine the transition from impacts that produce a single jet to those that produce two jets. Using high-speed X-ray imaging methods we show that vortex separation within the drop leads to the formation of a second jet long after the formation of the ejecta sheet. Using numerical simulations we develop a phase diagram for this transition and show that the capillary number is the most appropriate order parameter for the transition. © 2014 Cambridge University Press.
To Split or Not to Split: Dynamics of an Air Disk Formed under a Drop Impacting on a PoolJian, Zhen; Channa, Murad Ali; Kherbeche, Abderrahmane; Chizari, Hossain; Thoroddsen, Sigurdur T; Thoraval, M.-J. (Physical Review Letters, American Physical Society (APS), 2020-05-04) [Article]When a drop falls and impacts on a liquid pool, it entraps an air disk below the drop, which then contracts into a central bubble. Here, we use high-speed imaging and high-resolution numerical simulations to characterize the air-disk contraction dynamics for different liquid properties. We show that the air disk can contract into a single central bubble, form a toroidal bubble, or split vertically into two smaller bubbles. We demonstrate that the transitions between the different regimes can be separated by an Ohnesorge number, Ohe, based on the air-disk thickness. For the lowest Ohe, we find a new regime, where vortex shedding from the rim of the contracting air disk breaks the vertical symmetry and prevents the bubble from splitting in two.
Partial coalescence from bubbles to dropsZhang, F. H.; Thoraval, Marie-Jean; Thoroddsen, Sigurdur T; Taborek, P. (Journal of Fluid Mechanics, Cambridge University Press (CUP), 2015-10-07) [Article]The coalescence of drops is a fundamental process in the coarsening of emulsions. However, counter-intuitively, this coalescence process can produce a satellite, approximately half the size of the original drop, which is detrimental to the overall coarsening. This also occurs during the coalescence of bubbles, while the resulting satellite is much smaller, approximately 10 %. To understand this difference, we have conducted a set of coalescence experiments using xenon bubbles inside a pressure chamber, where we can continuously raise the pressure from 1 up to 85 atm and thereby vary the density ratio between the inner and outer fluid, from 0.005 up to unity. Using high-speed video imaging, we observe a continuous increase in satellite size as the inner density is varied from the bubble to emulsion-droplet conditions, with the most rapid changes occurring as the bubble density grows up to 15 % of that of the surrounding liquid. We propose a model that successfully relates the satellite size to the capillary wave mode responsible for its pinch-off and the overall deformations from the drainage. The wavelength of the primary wave changes during its travel to the apex, with the instantaneous speed adjusting to the local wavelength. By estimating the travel time of this wave mode on the bubble surface, we also show that the model is consistent with the experiments. This wavenumber is determined by both the global drainage as well as the interface shapes during the rapid coalescence in the neck connecting the two drops or bubbles. The rate of drainage is shown to scale with the density of the inner fluid. Empirically, we find that the pinch-off occurs when 60 % of the bubble fluid has drained from it. Numerical simulations using the volume-of-fluid method with dynamic adaptive grid refinement can reproduce these dynamics, as well as show the associated vortical structure and stirring of the coalescing fluid masses. Enhanced stirring is observed for cases with second-stage pinch-offs. Numerous sub-satellites are observed when the length of the top protrusion of the drop exceeds the Rayleigh instability wavelength. We also find a parameter regime where the focusing of more than one capillary wave can pinch-off satellites. One realization shows a sequence of three pinch-offs, where the middle one pinches off a toroidal bubble.