Gravity-driven clustering of inertial particles in turbulence
  We report a new kind of particle clustering caused purely by gravity, discovered in our simulation of particle-laden turbulence. Clustering in a vertical strip pattern forms when strong gravity acts on heavy particles. This phenomenon is explained by the skewness of the flow velocity gradient in the gravitational direction experienced by particles, which causes horizontal convergence of particles. 
Yongnam Park and Changhoon Lee
physics.flu-dyn