AJK2011-09012 INFLUENCE OF WATER-SPLASH FORMATION BY A HYDROPHILIC BODY PLUNGING INTO WATER

ABSTRACT The objective of this study is to understand the relationship between water-splash formation and the surface conditions of bodies plunging into the water's surface by considering hydrophilicity strength. A hydrophilic body (constructed with hydrogel), as well as an acrylic resin body, was created to understand the influence of hydrophilicity on splash formation. The strength of hydrophilicity was determined by investigating degrees of swelling. We obtained consecutive images of splash formation by using a high-speed CMOS camera. We show that water-splash formation is related to water-film formation by studying: 1) droplets formed at the film edge, 2) mushroomor dome-type splashes caused by film impinging, and 3) crowntype splash caused by film separation. The strength of hydrophilicity affects the splash-formation process of the mushroom-and crown-type splashes. The difference in formation process is caused when the film velocity increases with hydrophilicity. As the film velocity increases with strong hydrophilicity, the film flow separates from the body surface and an air cavity forms. Crown-type splashes form with hydrophilic bodies because such film separation occurs. Moreover, the relationship between the strength of hydrophilicity and film velocity was examined empirically. These results indicate that the hydrophilic body does not alter the splash-formation process. INTRODUCTION This study experimentally investigates the splash formed when a solid body plunges into water focusing on the influence of a hydrophilic body on subsequent splash events. The body impact on the water surface during a seaplane landing was studied by vo

AJK2011-03076 EFFECTS OF WALL CONDITION OF A PLUNGING BODY ON SPLASH

ABSTRACT Splashes generated by hydrogel sphere were simulated numerically and experimentally for investigating the effects of slip like mucus of living things. Numerical simulation using MPS (Moving Particle Semi-implicit) method was carried out. We defined the slip ratio as the swelling degree of hydrogel and installed the slip ratio into the MPS method. The swelling degree is the ratio of the weight of water against that of hydrogel. We simulated the splashes generated by the hydrogel spheres which had the different swelling degree plunging into water. As the evaluation of swelling degree on the surface of actual hydrogel spheres we also tested by using the hydrogel spheres plunging into water experimentally. The height of splash as a result of reaction of the air cavity became higher according to the increase of the swelling degree. The speed of hydrogel sphere sinking in water tank was also quicker in the numerical simulation. The reason of these results was that the velocity of water around the hydrogel sphere became quicker due to the slip on the surface

Acid mist formation in the electrowinning of copper

The formation of acid mist in the electrowinning of copper can result in a health hazard if the concentrations of the acid mist is too high. A study was carried out in a model electrowinning bath where the gas generation in an electrowinning bath was simulated by controlled gas injection. The breakup of the bubbles at the free surface controlled the mechanism for acid mist formation. The results showed that the bubble size and concentration played an important part in determining the droplet size and density that formed the acid mist. The amount of acid mist formed for different bubble concentration showed that the acid mist concentration above a model of the electrowinning bath decreases exponentially with distance from the bath surface. However, fine bubbles resulted in fine acid mist gives rise to droplets that can be carried away by the gas generated. The study identified means of reducing the acid mist concentration without the need to install complex gas cleaning and isolation equipment

Experimental Study on Kinematics and Dynamics of Breaking Waves in Deep Water

A new measurement technique called fiber optic reflectometer (FOR) was developed to investigate multiphase flows. The principle and setup of the FOR technique were introduced and applied to various experiments. Based on the coherently mixed signal between the Fresnel reflection off the fiber-liquid interface and the scattered signal off the object, such as a gas bubble, and a solid particle, this single probe technique is capable of simultaneously measuring the velocity of the object with a high accuracy and the phase of the fluid. In addition, bubble diameter, velocity, and void fraction were measured directly. By means of a simple modification of the FOR technique, solute concentration and refractive index change were measured with a greatly improved accuracy. This modified technique was used for measuring of a NaCl concentration in deionized water to validate a new normalization technique. In the second part of this thesis, a plunging breaking wave in deep water has been studied. Using the wave focusing method, a strong plunging breaker was generated with accuracy in the deep water condition in a two-dimensional wave tank. It was possible to describe the breaking process in detail using a high speed camera with a frame rate of 500 or 1000 fps. Four kinds of experimental techniques were employed or developed to investigate the plunging breaker. Bubble image velocimetry (BIV) and particle image velocimetry (PIV) were used to measure the velocity fields. The velocity fields of the highly aerated region were obtained from the BIV measurements. In addition, the modified PIV technique is capable of measuring the velocities in the entire flow field including the aerated region. Mean and turbulent properties were obtained by the ensemble average. The mean velocity, mean vorticity, and mean kinetic energy were examined over the entire flow field. In addition, the Reynolds stresses and turbulent kinetic energy were calculated with high temporal and spatial resolutions. Free surface elevation was obtained from wave gauge measurements. BIV and PIV images were also used to obtain the free surface elevation and the boundary of the aerated region for more accurate results. The FOR technique was used to obtain the void ratio at each splash-up region. Compressibility of the plunging breaker was considered. Mass flux, momentum flux, kinetic energy, and Reynolds stresses at each FOR station were recalculated using the void ratio obtained from the FOR measurements. All terms at the first splash-up region were highly overestimated more than 100 percent unless the void ratio was applied to the calculation of fluxes and energies. Compared with the fully developed first splash-up region, the overestimation at the second and third splash-up was less significant. However, most terms were overestimated by 20~30 percent when the void ratio was not considered

Sound emission on bubble coalescence: imaging, acoustic and numerical experim

Laboratory and numerical experiments are presented on the emission of sound on bubble coalescence. The aim was to better understand the fluid-dynamical mechanisms leading to sound emission. Bubbles were formed from a needle. Coordinated high-speed video and acoustic measurements demonstrated that the emission of high-amplitude sound coincided with the coalescence of a primary bubble with a smaller secondary. A numerical simulation was performed using a compressible level-set front-capturing code, in which a compressible gas and nearly compressible liquid are modelled by a single set of the Navier-Stokes equations with a generic equation of state for both phases. In the simulations, the spherical primary and secondary bubbles initially at acoustic equilibrium were brought into contact. The numerical calculations predicted the frequency of emitted sound and the bubble coalescence dynamics very well. The results suggest that the equalization of Laplace pressures could be the mechanism leading to sound emission

Numerical method to impose free-surface boundary conditions for local free-surface flows

Proceedings of the Seventh International Conference on Hydroscience and Engineering, Philadelphia, PA, September 2006. http://hdl.handle.net/1860/732This paper proposes a simple numerical technique to impose free-surface boundary conditions (FSBC) for free-surface flows governed by surface-vortex interactions. Accuracy and efficiency of this technique are examined through the analytical and experimental comparisons. The deformations of a free-surface and evolution of vortices at droplet impacts onto a water pool is reasonably reproduced by properly prescribing FSBC via the proposing method. Typical vortex rings are found to be initiated at the contacts between the droplet and receiving water-surface and to threedimensionally develop through a splashing process for interacting with a free-surface. The dependencies of flow field on an impact angle of the droplet are also discussed in this study

High-Fidelity Simulation and Novel Data Analysis of the Bubble Creation and Sound Generation Processes in Breaking Waves

Recent increases in computing power have enabled the numerical simulation of many complex flow problems that are of practical and strategic interest for naval applications. A noticeable area of advancement is the computation of turbulent, two-phase flows resulting from wave breaking and other multiphase flow processes such as cavitation that can generate underwater sound and entrain bubbles in ship wakes, among other effects. Although advanced flow solvers are sophisticated and are capable of simulating high Reynolds number flows on large numbers of grid points, challenges in data analysis remain. Specifically, there is a critical need to transform highly resolved flow fields described on fine grids at discrete time steps into physically resolved features for which the flow dynamics can be understood and utilized in naval applications. This paper presents our recent efforts in this field. In previous works, we developed a novel algorithm to track bubbles in breaking wave simulations and to interpret their dynamical behavior over time (Gao et al., 2021a). We also discovered a new physical mechanism driving bubble production within breaking wave crests (Gao et al., 2021b) and developed a model to relate bubble behaviors to underwater sound generation (Gao et al., 2021c). In this work, we applied our bubble tracking algorithm to the breaking waves simulations and investigated the bubble trajectories, bubble creation mechanisms, and bubble acoustics based on our previous works.Comment: conferenc