Spontaneous diffusion induced suction in stratified fluid: Experiments, computation, and theory for finite time collapse of bodies in strong stratification

We present experiments and computational predictions for a new phenomenon in which particulate suspended in stable stratification are attracted to vertical walls. The mechanism originates from a broken symmetry in the diffusion induced stratified flow exterior to a sphere near a vertical wall which creates an effective force of attraction arising through the viscous stress tensor. Computational simulations for a moving sphere reveal a surprising balance between the pressure and viscous stresses which allows a particle to coast, accelerating towards a vertical wall. The particle effectively screens the tremendous resistive lubrication forces in a low Reynolds number flow by significantly reducing the scale on which viscous drag dominates and slows the approach. Fixed body PIV experiments and simulations demonstrate the underlying diffusion induced flow structure responsible for the collapse. Reduced asymptotic modeling provides an analytical theory to explicitly calculate the pressure and viscous stresses that provides the coasting mechanism.