Clustering and dynamics of finite-size light particles in homogeneous isotropic turbulence

We investigate the effects of particle density and volume fraction on the clustering and dynamics of Taylor-scale light particles in forced homogeneous isotropic turbulence. Particle-resolved direct numerical simulations based on the immersed boundary method are employed to resolve the turbulent flow, particle–fluid interactions and particle–particle collisions. Voronoï analysis reveals that light particles (density ratio rho Subscript r Baseline less than 1 <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content"> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo>&lt;</mml:mo> <mml:mn>1</mml:mn> </mml:math> $\rho _r \lt 1$ ) exhibit stronger spatial clustering than heavy ( rho Subscript r Baseline greater than 1 <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content"> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo>&gt;</mml:mo> <mml:mn>1</mml:mn> </mml:math> $\rho _r \gt 1$ ) or neutrally buoyant ( rho Subscript r Baseline equals 1 <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content"> <mml:msub> <mml:mi>ρ</mml:mi> <mml:mi>r</mml:mi> </mml:msub> <mml:mo>=</mml:mo> <mml:mn>1</mml:mn> </mml:math> $\rho _r = 1$ ) ones, and the tendency of clustering for light particles also increases with volume fraction phi <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content"> <mml:mi>ϕ</mml:mi> </mml:math> $\phi$ . Light particles are found to preferentially accumulate in high-vorticity regions, and form large-scale clustering structures at a higher volume fraction phi equals 5 percent sign <mml:math xmlns:xlink="http://www.w3.org/1999/xlink" xmlns:mnf="http://cambridge.org/core/manifest" xmlns:cup="http://contentservices.cambridge.org" xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:m="http://cambridge.org/core/metadata" xmlns:core="http://cambridge.org/core" xmlns:c="http://cambridge.org/core/content"> <mml:mi>ϕ</mml:mi> <mml:mo>=</mml:mo> <mml:mn>5</mml:mn> <mml:mspace width="thinmathspace"/> <mml:mi mathvariant="normal">%</mml:mi> </mml:math> $\phi =5\,\%$ . Force balance analysis indicates that the pressure-gradient and added-mass effects play important roles in the dynamics of light particles, leading to their entrainment into vortical structures. Within dense clusters, frequent particle–particle collisions accelerate light particles to velocities far exceeding their velocity variance, resulting in a bimodal distribution of the particle velocity magnitudes and Reynolds numbers. Particle-pair statistics further quantify how particle collisions vary with particle inertia and volume fraction. These findings demonstrate that particle inertia, finite-size effects and particle–particle interactions act jointly to determine the clustering, collision dynamics and extreme-velocity events of light particles in turbulence. The results have direct implications for understanding and modelling suspensions of light particles in natural and industrial processes, such as the dispersion of micro-plastics in marine.