Phase-resolved two-phase flow experiments have been conducted to predict particle suspension and sedimentation within coupled particle-laden flows relevant to rotorcraft brownout conditions. Single phase and dual-phase PIV experiments have been conducted to study the interaction of a mobile sediment bed with characteristic flow structures similar to those within a rotor wake. Even though sediment transport has been extensively studied in the past, the rapidly evolving transient nature of brownout calls many of the simplifying assumptions that have been made to understand sediment transport mechanisms into question.

Image intensity based phase-separation and a hybrid PIV/PTV techniques have been implemented to identify the gas and solid phases as well as to the resolve multi-valued velocity displacements within a given interrogation region. A calibration technique to identify the measurement volume using size-brightness as well as PIV correlation based criteria has been outlined. Simultaneous velocity measurements of the fluid and dispersed phase in two vertical co-planar planes are analyzed to examine the role of vortex interaction and its subsequent breakdown on sediment transport process. The mobilization conditions and wall-normal flux of particulates by the vortex-wall interaction are reported and are correlated to the local vortex conditions such as proximity to the wall and subsequent decay. The effect of the

changing sediment bed profile on sediment transport rates is also studied. Modulation of mean and stochastic fluid flow properties due to the presence of particles and the effect of turbulent coupling between the particle and fluid momentum, as based on a modified drag law with dependence on particle Reynolds number as well as local volume fraction has been examined. A mesoscopic Eulerian formalism has been implemented to study the effect of particle inertia on the suspension process.