Shock-induced aerobreakup of a polymeric droplet

Abstract

Droplet atomization through aerobreakup is omnipresent in various natural and industrial processes. Atomization of Newtonian droplets is a well-studied area; however, non-Newtonian droplets have received less attention despite their being frequently encountered. By subjecting polymeric droplets of different concentrations to the induced airflow behind a moving shock wave, we explore the role of elasticity in modulating the aerobreakup of viscoelastic droplets. Three distinct modes of aerobreakup are identified for a wide range of Weber number $({\sim }10^2\unicode{x2013}10^4)$ and elasticity number $({\sim }10^{-4}\unicode{x2013}10^2)$ variation: these modes are vibrational, shear-induced entrainment and catastrophic breakup modes. Each mode is described as a three-stage process. Stage I is droplet deformation, stage II is the appearance and growth of hydrodynamic instabilities and stage III is the evolution of liquid mass morphology. It is observed that elasticity plays an insignificant role in the first two stages but a dominant role in the final stage. The results are described with the support of adequate mathematical analysis.

Shock-induced atomisation of a liquid metal droplet

“…The above definition of We is consistent for both incompressible and compressible flows. Several references provide a detailed overview of the exploding-wire technique and its application in shock-wave generation (Liverts et al 2015;Sembian et al 2016;Sharma et al 2021c;Chandra et al 2023). Compared with conventional diaphragm-based shock tubes, the exploding-wire technique offers advantages such as smaller test facilities, easier operation, a wide range of shock Mach numbers (from 1 to 6 Sembian et al 2016) and high repeatability between tests.…”

“…Although several recent experimental studies have attempted to investigate some of these aspects (Theofanous et al 2004;Theofanous & Li 2008;Biasiori-Poulanges & El-Rabii 2019;Liang et al 2020;Wang et al 2020;Jackiw & Ashgriz 2021), a comprehensive study providing benchmark measurement data for numerical simulation, which covers a wide parametric range and the complete evolution dynamics of the interaction phenomenon, is still lacking. In our previous works we attempted to fill this gap by investigating the high Weber number atomisation of Newtonian and viscoelastic droplets using high-quality experimentation (Sharma et al 2021c;Chandra et al 2023). In this study we extend our efforts to explore the atomisation dynamics of a liquid metal droplet.…”

“…The present work uses the same description for the two modes. Notably, the absence of Rayleigh-Taylor surface instability at high We ∼ O( 1000) is debatable in literature (Joseph, Belanger & Beavers 1999;Chandra et al 2023;Mansoor & George 2023).…”

“…The aerodynamic breakup of a liquid droplet is a high-speed phenomenon where the droplet disintegration is completed within the time scales of O(100) μs, particularly at higher Weber numbers. Previous studies in this regime focused on breakup and deformation characteristics of the droplet and morphology of the atomizing droplet (Theofanous, Li & Dinh 2004;Theofanous & Li 2008;Meng & Colonius 2015;Poplavski et al 2020;Wang et al 2020;Sharma et al 2021c;Chandra et al 2023). Liang et al (2020) investigated the influence of the vapour cavity on the droplet's atomisation behaviour and found the dynamics to be dependent on the size and eccentricity of the vapour cavity.…”

“…Liang et al (2020) investigated the influence of the vapour cavity on the droplet's atomisation behaviour and found the dynamics to be dependent on the size and eccentricity of the vapour cavity. Chandra et al (2023) investigated the role of polymer elasticity in controlling the breakup morphology of secondary droplets. It should be noted that the high-speed interaction dynamics is difficult to perceive through numerical and experimental means due to the short time and length scales of the breakup phenomenon.…”