Particulate mixing in a turbulent serpentine duct
Direct numerical simulations of particles in a serpentine duct were conducted at bulk flow Stokes numbers between 0.125 and 6. The geometrical curvature causes particles to depart direction from the mean flow. Above a Stokes number of about unity, a reflection layer forms along the outer curve of the bend. Reflectional mixing creates regions of nearly uniform particle mean velocity and kinetic energy. Particles leave the inner bend in a plume that separates from the inner wall at low Stokes number. At higher Stokes number, the plume splits in two, adding an upper part consisting of ballistic particles, that do not follow the geometrical curvature. When the Stokes number is low, the instantaneous 3-D distribution of particles visualizes wall streaks. But at higher Stokes number, particles disperse out of the reflection layer and form large scale puffs in the central portion of the duct.