arXiv subjects

Patricia Vega-Martínez

Publications and source records attributed to Patricia Vega-Martínez.

5 recordsLinked to original sources

arXiv2021

Air Entrapment and its effect on Pressure Impulses in the slamming of a Flat Disc on Water

The presence of ambient air in liquid-slamming events plays a crucial role in influencing the shape of the liquid surface prior to the impact, and the distribution of loads created upon impact. We study the effect of trapped air on impact loads in a simplified geometry, by slamming a horizontal flat disc onto a stationary water bath at a well-controlled velocity. We show how air trapping influences pressure peaks at different radial locations on the disc, how the pressure impulses are affected, and how local pressure impulses differ from those obtained from area-integrated (force) impulses at impact. More specifically, we find that the air layer causes a gradual buildup of the load before the peak value is reached, and show that this buildup follows inertial scaling. Further, the same localised pressure impulse at the disc centre are found to be lower than the corresponding (area-integrated) force impulse on the entire disc. While the (area-integrated) force impulses are close to the classical result of Batchelor (1967, section 6.10) and Glasheen & McMahon (1996), the localised pressure impulses at disc center, where the trapped air layer is at its thickest, are found to lie closer to the theoretical estimation by Peters et al. (2013) for an air-cushioned impact.

physics.flu-dyn↗

arXiv2020

Growth of a bubble cloud in CO2-saturated water in microgravity

The diffusion-driven growth of a dense cloud of bubbles immersed in a gas-supersaturated liquid is a problem that finds applications in several modern technologies such as solvent-exchange micro-reactors, nanotechnology or the manufacturing of foamy materials. However, under Earth's gravity conditions, these dynamics can only be observed for a very limited time if the cloud is not attached to a surface, due to the action of buoyancy, i.e. of gravity effects. Here, we present experimental observations of the time evolution of dense bubble clouds growing in CO$_2$-supersaturated water in microgravity conditions. We report the existence of three regimes where the bubble cloud exhibits different growth rates. At short times, each bubble grows independently following the Epstein--Plesset equation. Later on, bubbles start to interact with each other and their growth rate diminishes as they compete for the available CO$_2$. When this happens, the growth rate slows down. This occurs earlier the deeper the bubble is in the cloud. Finally, at long times, only those bubbles on the husk continue growing. These regimes may be qualitatively described by a mathematical model where each individual bubble grows in the presence of a constellation of point mass sinks. Despite the model being only valid for dilute bubble clouds, its predictions are consistent with the experimental observations, even though the bubble clouds we observe are rather dense.

cond-mat.soft↗

arXiv2019

Hydroelastic effects during the fast lifting of a disc from a water surface

Here we report the results of an experimental study where we measure the hydrodynamic force acting on a plate which is lifted from a water surface, suddently starting to move upwards with an acceleration much larger than gravity. Our work focuses on the early stage of the plate motion, when the hydrodynamic suction forces due to the liquid inertia are the most relevant ones. Besides the force, we measure as well the acceleration at the center of the plate and the time evolution of the wetted area. The results of this study show that, at very early stages, the hydrodynamic force can be estimated by a simple extension to the linear exit theory by Korobkin (2013), which incorporates an added mass to the body dynamics. However, at longer times, the measured acceleration decays even though the applied external force continues to increase. Moreover, high-speed recordings of the disc displacement and the radius of the wetted area reveal that the latter does not change before the disc acceleration reaches its maximum value. We show in this paper that these phenomena are caused by the elastic deflection of the disc during the initial transient stage of water exit. We present a linearised model of water exit that accounts for the elastic behaviour of the lifted body. The results obtained with this new model agree fairly well with the experimental results.

physics.flu-dyn↗

arXiv2017

Transient effects in the translation of bubbles insonated with acoustic pulses of finite duration

The translation of a bubble under the action of an acoustic forcing finds applications in fields ranging from drug delivery to sonoluminesce. This phenomenon has been widely studied for cases where the amplitude of the forcing remains constant over time. However, in many practical applications, the duration of the forcing is not long enough for the bubble to attain a constant translational velocity, mainly due to the effect of the history force. Here, we develop a formulation, valid in the limit of very viscous flow and small-amplitude acoustic forcing, that allows us to describe the transient dynamics of bubbles driven by acoustic pulses consisting of a finite number of cycles. We also present an asymptotic solution to this theory for the case of a finite-duration sinusoidal pressure pulse. This solution takes into account both the history integral term and the transient period that the bubble needs to achieve steady radial oscillations, being the former dominant during most of the acceleration process. Moreover, by introducing some additional assumptions, we derive a simplified formula that describes fairly well the time evolution of the bubble velocity. Using this solution we show that the convergence to the steady translational velocity, given by the so-called Bjerknes force, occurs rather slowly, namely as $τ^{-1/2}$, which explains the slow convergence of the bubble velocity and stresses the importance of taking into account the history force.

physics.flu-dyn↗

arXiv2017

Drop tower setup to study the diffusion-driven growth of a foam ball in supersaturated liquids in microgravity conditions

The diffusion-driven growth of a foam ball is a phenomenon that appears in many manufacturing process as well as in a variety of geological phenomena. Usually these processes are greatly affected by gravity, as foam is much lighter than the surrounding liquid. However, the growth of the foam free of gravity effects is still very relevant, as it is connected to manufacturing in space and to the forma- tion of rocks in meteorites and other small celestial bodies. The aim of this research is to investigate experimentally the growth of a bubble cloud growing in a gas-supersaturated liquid in microgravity conditions. Here, we describe the ex- periments carried out in the drop tower of the Center of Ap- plied Space Technology and Microgravity (ZARM). In few words, a foam seed is formed with spark-induced cavitation in carbonated water, whose time evolution is recorded with two high-speed cameras. Our preliminary results shed some light on how the size of the foam ball scales with time, in particular at times much longer than what could be studied in normal conditions, i.e. on the surface of the Earth, where the dynamics of the foam is already dominated by gravity after several milliseconds.

physics.flu-dyn↗