Comparison of simulation and experiments for multimode aerodynamic breakup of a liquid metal column in a shock-induced cross-flow

Abstract

While the mechanisms that drive breakup and aerodynamic dispersion of traditional liquids such as water have been extensively studied, it is not yet clear if models for traditional liquids can be used to accurately describe the behavior of molten metals. In this paper, multiphase simulations with the interface-capturing combined level-set volume-of-fluid approach are used to provide time-resolved morphology and breakup data for a liquid column subject to a shock-induced cross-flow. For the first time, numerical simulation of the behavior of a liquid metal (Galinstan alloy composed of gallium, indium, and tin) is compared to the well-documented behavior of water. Simulations consider a gas cross-flow Weber number between 10 and 12, which produces a multimode breakup morphology consisting of multiple baglike structures. Up to bag breakup, we confirm that the deformation rate of Galinstan follows the same dependence on the gas cross-flow Weber number as ordinary liquids when time is nondimensionalized by including the liquid-gas density ratio. Moreover, we determine that the appearance of a central stem along the column upstream surface in multimode bag breakup is consistent with the occurrence of Rayleigh-Taylor instability. We also resolve bag stretching and fragmentation, to the full extent allowed by our computational resources, and carry out a direct comparison with the measurements of size and velocity of secondary droplets from high-speed digital inline holography. For Galinstan, we illustrate the differences between simulation and experiment that emerge because of the modification of the surface properties of the metal exposed to air.

Shock-induced atomisation of a liquid metal droplet

“…Variation can arise due to experimental uncertainties. As observed in the literature (Chen et al 2018;Arienti et al 2019;Hopfes et al 2021b), the uncertainty in droplet deformation increases with an increase in the Weber number values. Here, deformation is measured at much higher Weber number values, and higher uncertainty is expected.…”

“…Within the experimental uncertainty, a similar behaviour of droplet deformation is observed till the first instance of droplet breakup (t * ∼ 0.6, in all cases). Previous studies (Chen et al 2018;Arienti et al 2019;Hopfes et al 2021a) have also shown a similar behaviour of early stage droplet deformation between Galinstan and DI water test cases. After t * > 0.6, droplet atomisation begins, making it difficult to measure the cross-stream diameter accurately.…”

“…However, differences were observed in the shape of fragments, with irregular-shaped daughter droplets formed in the case of the Galinstan column due to the oxide layer formed on the exposed surface of droplets. Similar observations were made through numerical simulation (Arienti et al 2019). Hopfes et al (2021a,b) studied the atomisation of Galinstan droplets for moderate Weber numbers (We = 10-104) and found similar breakup modes and critical Weber number values for regime transition for Galinstan and conventional fluids with Oh < 0.1.…”

“…2014; Arienti et al. 2019; Handschuh-Wang, Stadler & Zhou 2021 b ). This range is primarily due to the presence of oxidizing conditions in which measurements were undertaken.…”

“…The exact values of its fluid properties are debatable in the literature. Surface tension values are reported in the range of 500-700 mN m −1 (Liu et al 2011;Plevachuk et al 2014;Arienti et al 2019;Handschuh-Wang, Stadler & Zhou 2021b). This range is primarily due to the presence of oxidizing conditions in which measurements were undertaken.…”