Special Issue "Hydrodynamics of a Drop"

Submission Deadline: 20 September 2019 (closed)
Guest Editors
Yuli D. Chashechkin, Russian Academy of Sciences, Moscow, Russia.

Summary

Although the hydrodynamics and acoustics of a drop impact have been intensively studied for more than a century and a half, a number of questions posed in the pioneer works by Rogers, Worthington, Thomson still remain unanswered. The nature of the formation of thin filaments in a pattern of the substance of falling drop distribution in target fluid, which retains its discrete properties for quite a long time despite the smoothing effect of molecular diffusion; the fine structure of the velocity field, including fast and slow jetlets, the sound emission mechanism, and a number of other issues, requires study. The implementation of new tools such as high-speed video-cameras, controlled intensive sources of light, highly sensitive hydrophones and microphones, contact sensors allows obtaining large amounts of data necessary for a more detailed description of the properties of flows, the relationship of hydrodynamic and hydroacoustic processes. The purpose of this issue is to present the results of current research of processes accompanying the immersion of freely falling drop in a wide range of pairs of contacting fluids, both miscible and immiscible, pure single-component and multi-component solutions or suspensions, as well as new theoretical approaches to the description of the waves, dynamics and the structure of the cascade of complex phenomena, including those studied as the basis for practical applications.


Keywords
drop water impact sound, immersion, flows, pattern of flows, experiment

Published Papers
  • Spreading of a Multicomponent Drop in Water: Solutions and Suspensions
  • Abstract The distribution of material resulting from the impact of a freely falling drop with a target liquid has been studied by photo and video registration methods. Different cases have been investigated by considering drops made of aqueous solutions (ink, salt, acid) and including fine solid particles (i.e., suspensions). New features have been observed in terms of flow dynamics and thin components produced as a result of the impact (such as banded elements, ligaments, and vortices at the surface of the liquid). In particular, the characteristics of emerging netlike structures have been found to depend on the size of the suspension… More
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  • Acoustic Shock Emission in a Collision of a Drop with Water Surface
  • Abstract The collision of droplets with a water surface is being actively developed in the interests of many applied problems—transfer of matter through the ocean-atmosphere boundary, underwater acoustic noise of the marine environment, measurement of precipitation intensity, various technologies, and much more. One of the research priorities is acoustic radiation, in particular, shock sound arising at the moment a drop contacts the surface. The impact of the drop is preceded by processes that affect the shape of the drop, because of which it noticeably deviates from the spherical one. As a result, the final (contact) velocity changes–one of the most important… More
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  • Oscillations of an Inviscid Encapsulated Drop
  • Abstract The problem relating to the small-amplitude free capillary oscillations of an encapsulated spherical drop is solved theoretically in the framework of asymptotic methods. Liquids are supposed to be inviscid and immiscible. The formulas derived are presented for different parameters of the inner and outer liquids, including densities, thickness of the outer liquid layer, and the surface and interfacial tension coefficients. The frequencies of oscillation of the encapsulated drop are studied in relation to several “modes” which can effectively be determined in experiments by photo and video analysis. The results are presented in terms of oscillation frequencies reported as a function… More
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  • Fast Superfine Components and Sound Packets in Phenomena Induced by the Impact of a Drop on a Target Fluid in Quiescent Conditions
  • Abstract The structure of the flow and the acoustic signals generated by the impact of a freely falling drop of water with an underlying quiescent fluid have been investigated for droplets having diameter 0.5 cm and a contact velocity in the range 1.5 < U < 5 m/s. The experimental study has been supported by high-resolution videos of the flow (as seen from above and from the side). The evolution of ejecta, spikes, droplets spray, cavity, splash, secondary cavity, streamer, secondary droplets and sequence of capillary waves is reported accordingly. In particular, perturbations of the smoothed free surface with transverse dimensions… More
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  • Complete Coalescence, Partial Bounce and Rebound: Different Regimes Resulting from the Interaction of a Free Falling Drop with a Target Fluid
  • Abstract The interaction of a falling drop (diluted aqueous solution of ink in various concentrations) with a target fluid (partially degassed tap water) has been tracked by means of high-resolution video recording and photography. The experimental setup has carefully been prepared in order to preserve the axial symmetry of initial conditions. Three regimes of interaction have been identified accordingly (depending on the drop velocity as controlled by the distance of fall): rapid droplet coalescence, rebound with the conservation of the drop volume and shape, and partial coalescence. Previous findings are recovered and confirmed, and enriched with heretofore unseen observations of complex… More
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