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Dispersion of finite size droplets and solid particles in isotropic turbulence


Turbulent disperse two-phase flows, of either fluid/fluid or fluid/solid type, are common in natural phenomena and engineering devices. Notable examples are atmospheric clouds, i.e.

dispersed liquid water droplets and ice particles in a complex turbulent flow, and spray of fuel

droplets in the combustion chamber of internal combustion engines. However, the physics of

the interaction between a dispersed phase and turbulence is not yet fully understood. The

objective of this study is to compare the dispersion of deformable finite size droplets with

that of solid particles in a turbulent flow in the absence of gravity, by performing Direct

Numerical Simulation (DNS). The droplets and the particles have the same diameter, of the

order of the Taylor’s microscale of turbulence, and the same density ratio to the carrier flow.

The solid particle-laden turbulence is simulated by coupling a standard projection method

with the Immersed Boundary Method (IBM). The solid particles are fully resolved in space

and time without considering particle/particle collisions (two-way coupling). The liquid

droplet-laden turbulence is simulated by coupling a variable-density projection method with

the Accurate Conservative Level Set Method (ACLSM). The effect of the surface tension

is accounted for by using the Ghost Fluid Method (GFM) in order to avoid any numerical

smearing, while the discontinuities in the viscous term of the Navier-Stokes equation are

smoothed out via the Continuum Surface Force approach. Droplet/droplet interactions are allowed (four-way coupling). The results presented here show that in isotropic turbulence

the dispersion of liquid droplets in a given direction is larger than that of solid particles due

to the reduced decay rate of turbulence kinetic energy via the four-way coupling effects of

the droplets.

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