Droplet impact and penetration on series of parallel tubes

Impact and penetration of a liquid droplet on a substrate having a line of parallel capillary openings drilled along its thickness is experimentally studies. Different regimes of droplet penetration are identified. At low impact velocities, the droplet impacts on the substrate, spreads, and penetrates into the substrate mainly due to the capillary action in each tubular hole. At higher impact velocities, the droplet impacts on the substrate, spreads and penetrates due to the droplet inertia, and then penetrates further due to the capillary action. Threshold velocities for liquid penetration into capillary tubes are identified. Two penetration regimes, capillary and inertia driven regimes, have been studied extensively for a range of parameters related to droplet impact on a line of parallel capillary openings. Index Terms—Droplet impact, parallel capillary tubes, penetration, liquid spread

Nonlinear Bubble Interactions in Acoustic Pressure Fields

The systems consisting of a two-phase mixture, as clouds of bubbles or drops, have shown many common features in their responses to different external force fields. One of particular interest is the effect of an unsteady pressure field applied to these systems, case in which the coupling of the vibrations induced in two neighboring components (two drops or two bubbles) may result in an interaction force between them. This behavior was explained by Bjerknes by postulating that every body that is moving in an accelerating fluid is subjected to a 'kinetic buoyancy' equal with the product of the acceleration of the fluid multiplied by the mass of the fluid displaced by the body. The external sound wave applied to a system of drops/bubbles triggers secondary sound waves from each component of the system. These secondary pressure fields integrated over the surface of the neighboring drop/bubble may result in a force additional to the effect of the primary sound wave on each component of the system. In certain conditions, the magnitude of these secondary forces may result in significant changes in the dynamics of each component, thus in the behavior of the entire system. In a system containing bubbles, the sound wave radiated by one bubble at the location of a neighboring one is dominated by the volume oscillation mode and its effects can be important for a large range of frequencies. The interaction forces in a system consisting of drops are much smaller than those consisting of bubbles. Therefore, as a first step towards the understanding of the drop-drop interaction subject to external pressure fluctuations, it is more convenient to study the bubble interactions. This paper presents experimental results and theoretical predictions concerning the interaction and the motion of two levitated air bubbles in water in the presence of an acoustic field at high frequencies (22-23 KHz)

IMECE2005-81757 FLOW INDUCED DYNAMICS OF A PINNED DROPLET ON THE SURFACE OF CHANNEL

ABSTRACT Dynamic behavior of a droplet adhering to the surface of a channel has been modeled under the influence of surrounding fluid. The numerical solution is based on solving Navier-Stokes equations for Newtonian liquids. The study includes the effect of interfacial forces with constant surface tension, also effect of adhesion between the wall and droplet accounted by implementing contact angle at the wall. The Volume-Of-Fluid method is used to numerically determine the deformation of free surface. Droplet deformation and final shapes have been predicted. A reduction in the surface tension allows the droplet to deform much easier. However, an increase in the fluid viscosity, although increases the shear force on the droplet, may not result in the deformation at high surface tension. It is shown that deformation of droplet significantly influences structure of channel flow. Effects of liquid droplet and channel fluid properties, namely density and viscosity, inlet velocity, surface tension and channel geometry on dynamics of the problem have been studied. Two different outcomes have been considered: the first one droplet with equilibrium shape and the other one when breakup of the droplet occurs. The border line between the disintegration region and equilibrium region is determined for different droplet surface tensions

A Droplet Deformation And Fragmentation In A High Speed Air Jet

Paper presented at 2018 Canadian Society of Mechanical Enginees International Congress, 27-30 May 2018.Impingement of a gas jet on a suspended water droplet is modeled numerically. The jet velocity and jet diameter effects on the penetration length and the shape of the gas tunnel inside the droplet are studied. The gas tunnel inside the droplet is smaller on the windward and larger on the leeward of the droplet. Different types of breakup processes are identified and categorized according to jet to droplet diameter ratio, as well as the droplet Weber number

Numerical Investigation of Head-on Binary Drop Collisions in a Dynamically Inert Environment

The results of three-dimensional numerical simulations of drop collisions without the effect of a surrounding environment are presented. The numerical model is based on an Eulerian, finite-difference, Volume-of-Fluid method. Surface tension is included using the Continuum Surface Force method. Head-on collisions using equal size drops with three different fluid properties of water, mercury and tetradecane are presented. Various drop diameters ranging from 200 μm to 5 mm are considered. A separation criterion based upon deformation data is found. The lower critical Weber numbers are found for mercury and water drops while tetradecane drops did not result in separation for the range of Weber numbers considered. The effect of Reynolds number is investigated and regions of permanent coalescence and separation are plotted in the Weber-Reynolds number plane. The role of viscosity and its effect on dissipation is also investigated. Finally, the validity of the assumptions made in some of the collision models is assessed

The influence of acoustic field induced by HRT on oscillation behavior of a single droplet

This paper presents an experimental and theoretical study on the effects of an acoustic field induced by Hartmann Resonance Tube (HRT) on droplet deformation behavior. The characteristics of the acoustic field generated by HRT are investigated. Results show that the acoustic frequency decreases with the increase of the resonator length, the sound pressure level (SPL) increases with the increase of nozzle pressure ratio (NPR), and it is also noted that increasing resonator length can cause SPL to decrease, which has rarely been reported in published literature. Further theoretical analysis reveals that the resonance frequency of a droplet has several modes, and when the acoustic frequency equals the droplet's frequency, heightened droplet responses are observed with the maximum amplitude of the shape oscillation. The experimental results for different resonator cavity lengths, nozzle pressure ratios and droplet diameters confirm the non-linear nature of this problem, and this conclusion is in good agreement with theoretical analysis. Measurements by high speed camera have shown that the introduction of an acoustic field can greatly enhance droplet oscillation, which means with the use of an ultrasonic atomizer based on HRT, the quality of atomization and combustion can be highly improved

Numerical investigation of the aerodynamic breakup of a parallel moving droplet cluster

The present work examines numerically the aerodynamic breakup of a cluster of Diesel droplets moving in parallel with respect to the gas flow. Two- and three-dimensional simulations of the incompressible Navier-Stokes equations together with the VOF method are performed for Weber (We) numbers in the range of 5 up to 60 and non-dimensional distance between the droplets (H/D0) ranging from 1.25 to 20. The numerical results indicate that the proximity of droplets affects their breakup for distances H/D0≤5. For low droplet proximity distances (H/D0≤2.5), the droplets experience the so-called shuttlecock breakup mode, which has been also identified for droplets in tandem formations in a previous authors’ work and is characterized by an oblique peripheral stretching of the droplet. With decreasing H/D0 the breakup initiation time decreases, while the drag coefficient increases relative to that of isolated droplets. When the distance between the droplets is low enough (H/D0<1.5), this can result in critical We number, i.e. minimum We number leading to breakup, lower than that of an isolated droplet at the same conditions

Mapping outcomes of liquid marble collisions

© 2019 The Royal Society of Chemistry. Liquid marbles (LMs) have many promising roles in the ongoing development of microfluidics, microreactors, bioreactors, and unconventional computing. In many of these applications, the coalescence of two LMs is either required or actively discouraged, therefore it is important to study liquid marble collisions and establish parameters which enable the desired collision outcome. Recent reports on LM coalescence have focused on either two mobile LMs colliding, or an accelerating LM hitting a sessile LM with a backstop. A further possible scenario is the impact of a mobile LM against a non-supported static LM. This paper investigates such a collision, using high-speed videography for single-frame analysis. Multiple collisions were undertaken whilst varying the modified Weber number (We∗) and offset ratios (X∗). Parameter ranges of 1.0 0.25, and We∗ 1.55 resulted in 100% non-coalescence. Additionally, observations of LMs moving above a threshold velocity of 0.6 m s -1 have revealed a new and unusual deformation. Comparisons of the outcome of collisions whilst varying both the LM volume and the powder grain size have also been made, revealing a strong link. The results of this work provide a deeper understanding of LM coalescence, allowing improved control when designing future collision experiments

Numerical analysis of hydraulic jumps using OpenFOAM

[EN] The present paper deals with a hydraulic jump study, characterization and numerical modeling. Hydraulic jumps constitute a common phenomenon in the hydraulics of open channels that increases the shear stress on streambeds, so promoting their erosion. A three-dimensional computational fluid dynamics model is proposed to analyze hydraulic jumps in horizontal smooth rectangular prismatic open-air channels (i.e., the so-called classical hydraulic jump). Turbulence is modeled using three widely used Reynolds-averaged Navier Stokes (RANS) models, namely: Standard k &#949;, RNG k &#949;, and SST k &#969;. The coexistence of two fluids and the definition of an interface between them are treated using a volume method in Cartesian grids of several element sizes. An innovative way to deal with the outlet boundary condition that allows the size of the simulated domain to be reduced is presented. A case study is conducted for validation purposes (FR1 &#8764; 6.10, Re1 &#8764; 3.5·105): several variables of interest are computed (sequent depths, efficiency, roller length, free surface profile, etc.) and compared to previous studies, achieving accuracies above 98% in all cases. In the light of the results, the model can be applied to real-life cases of design of hydraulic structures.This research was conducted thanks to the funding provided by the VALi + D R&D Program of the Generalitat Valenciana (Spain). It would not have been possible without the contribution of Daniel Valero and Beatriz Nacher of the Hydraulics Laboratory of the School of Civil Engineering (Universitat Politecnica de Valencia).Bayón Barrachina, A.; López Jiménez, PA. (2015). Numerical analysis of hydraulic jumps using OpenFOAM. Journal of Hydroinformatics. 17(4):662-678. https://doi.org/10.2166/hydro.2015.041S66267817