THE EFFECT OF STREAMWISE BRAID VORTICES ON THE PARTICLE DISPERSION INA PLANE MIXING LAYER .2. NONLINEAR PARTICLE DYNAMICS

A computational investigation of the nonlinear dynamics of heavy parti cles in a row of counterrotating strained vortices is presented. By tr acking the particles numerically in the quasi-two-dimensional fluid ve locity field, information is obtained on the nature of their trajector ies, as well as on probability distribution functions and potential ac cumulation regions. The particle behavior is discussed as a function o f the dimensionless strain rate, the particle Stokes number St, and th e dimensionless gravity parameter Fr. Only for very low values of the St can the particles accumulate at the vortex centers. For moderate va lues of St, they remain trapped on closed trajectories around the vort ex centers. Increasing St leads to periodic open trajectories that all ow for spanwise transport of the particles. Further bifurcations lead to the generation of multiple trajectories, as well as to subharmonic solutions. Eventually, intermittent and chaotic particle dynamics are observed. In the chaotic regime, a simplified flow model is employed i n order to derive various scaling laws for the particle concentration field. For strong levels of gravity, the accumulation of large numbers of particles is observed in the upwelling regions predicted in part I of the present investigation [B. Marcu and E. Meiburg, Phys. Fluids 8 , 715 (1996)]. (C) 1996 American Institute of Physics.