High-fidelity simulations of bubble, droplet and spray formation in breaking waves

Abstract

High-fidelity simulations of wave breaking processes are performed with a focus on the small-scale structures of breaking waves, such as bubble/droplet size distributions. Very large grids (up to 12 billion grid points) are used in order to resolve the bubbles/droplets in breaking waves at the scale of hundreds of micrometres. Wave breaking processes and spanwise three-dimensional interface structures are identified. It is speculated that the Görtler type centrifugal instability is likely more relevant to the plunging wave breaking instabilities. Detailed air entrainment and spray formation processes are shown. The bubble size distribution shows power-law scaling with two different slopes which are separated by the Hinze scale. The droplet size distribution also shows power-law scaling. The computational results compare well with the available experimental and computational data in the literature. Computational difficulties and challenges for large grid simulations are addressed.

Scale separation and dependence of entrainment bubble-size distribution in free-surface turbulence

“…and hence not related to the Hinze scale r H as is often assumed (Deane & Stokes 2002;Wang et al 2016). Inspired by the diagram of the (L, q)-plane in Brocchini & Peregrine (2001), we derive a (r, )-plane prediction of when air entrainment occurs in free-surface turbulence (FST).…”

A mechanistic model of bubble entrainment in turbulent free surface flows

“…The direct numerical simulation of laboratory scale experiments however, has been achieved with today's supercomputing power (Wang et al, 2014;Dommermuth et al, 2014;Lubin and Glockner, 2015). For a simulation using 9 10 grid points on a small scale tank of about cm 20 L  the grid size would be 200 m  and the smallest bubble size that can be resolved would be 1 mm when considering only about 5 grid points per bubble diameter.…”

Biological fluid dynamics of airborne COVID-19 infection

“…a contaminated handkerchief). Infection takes place if the susceptible individual touches his/her mouth, nose or eyes after picking up the virus by touching an infected surface (Wang et al 2020).…”

“…This is not an easy task, as fragmentation is associated with changes of the interface topology and the development of cusps when two interfaces reconnect (see the review of Scardovelli and Zaleski 1999). This is an actively investigated area of research due to its relevance for many engineering applications, which will likely take advantage of the continuous increase of the computational power (Wang et al 2016).…”