Rarefaction effects in head-on collision of two near-critical droplets

Chen，Tao1; Wu，Lei1; Wang，Lian Ping1,2,3,4; Chen，Shiyi1,2,3,4,5

2023-07-01

10.1016/j.ijmultiphaseflow.2023.104451

International Journal of Multiphase Flow   Impact Factor & Quartile

0301-9322

1879-3533

The head-on collision of two droplets near the critical point is investigated based on the Boltzmann-BGK equation. Gauss–Hermite quadratures with different degree of precision are used to solve the kinetic equation, so that the solutions truncated at the Navier–Stokes order and non-continuum (i.e., rarefied fluid dynamics) solutions can be compared. When the kinetic equation is solved with adequate accuracy, prominent variations of the vertical velocity (the collision is in the horizontal direction), the viscous stress components, and droplet morphology are observed during the formation of liquid bridge, which demonstrates the importance of the rarefaction effects and the failure of the Navier–Stokes equation. The rarefaction effects change the topology of streamlines near the droplet surface, suppress the high-magnitude vorticity concentration inside the interdroplet region, and promote the vorticity diffusion around outer droplet surface. Two physical mechanisms responsible for the local energy conversion between the free and kinetic energies are identified, namely, the total pressure-dilatation coupling effect and the interaction between the density gradient and strain rate tensor. An energy conversion analysis is performed to show that the rarefaction effects can enhance the conversion from free energy to kinetic energy and facilitate the discharge of the gas interval along the vertical direction, thereby boosting droplet coalescence. Furthermore, the magnitude and the spatial oscillation frequency of the Lamb vector divergence inside the gas interval are shown to be suppressed by the rarefaction effects. It is found that the dynamic process in the gas interval is closely associated with the interaction between the adjacent positive and negative regions of the Lamb vector divergence.

Boltzmann equation Droplet collision Gas interval structure Rarefied fluid dynamics

SCI

English

First ; Corresponding

Guangdong-Hong Kong-Macao Joint Lab-oratory for Data-Driven Fluid Mechanics and Engineering Applications in China[2020B1212030001]

Mechanics

Mechanics

WOS:000965576300001

PERGAMON-ELSEVIER SCIENCE LTD

ENGINEERING

2-s2.0-85151035244

Scopus

1.Department of Mechanics and Aerospace Engineering,Southern University of Science and Technology,Shenzhen,518055,China
2.Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou),Guangzhou,1119 Haibin Road, Nansha District,511458,China
3.Guangdong Provincial Key Laboratory of Turbulence Research and Applications,Center for Complex Flows and Soft Matter Research and Department of Mechanics and Aerospace Engineering,Southern University of Science and Technology,Shenzhen,Guangdong,518055,China
4.Guangdong-Hong Kong-Macao Joint Laboratory for Data-Driven Fluid Mechanics and Engineering Applications,Southern University of Science and Technology,Shenzhen,518055,China
5.Eastern Institute for Advanced Study,Yongriver Institute of Technology,Ningbo,315200,China

Chen，Tao,Wu，Lei,Wang，Lian Ping,et al. Rarefaction effects in head-on collision of two near-critical droplets[J]. International Journal of Multiphase Flow,2023,164.

Chen，Tao,Wu，Lei,Wang，Lian Ping,&Chen，Shiyi.(2023).Rarefaction effects in head-on collision of two near-critical droplets.International Journal of Multiphase Flow,164.

Chen，Tao,et al."Rarefaction effects in head-on collision of two near-critical droplets".International Journal of Multiphase Flow 164(2023).