Numerical and wind tunnel studies of particle transport, deposition, and rebound in turbulent flows

Particle transport, deposition, and rebound in turbulent flows were explored through wind tunnel experiments and mathematical modeling. A turbulent boundary layer was generated with a rectangular bar placed in a wind tunnel. Monodisperse particles were generated with a vibrating orifice particle generator. Particle size ranged from about 2 mum to about 4.5 mum while the free stream velocity ranged from 3.3 m/s to 15.3 m/s. Smooth receptor surface stripes (each with a size of 1.27 cm x 12 cm) were placed downstream at intervals of 10.16 cm for particle deposition and rebound measurements. Detailed turbulence characteristics of the boundary layer were measured with a high response frequency hot wire anemometer while particle deposition and rebound were studied under the same aerodynamic conditions.;Results of the wind tunnel experiments show that dry deposition strongly depends on particle and turbulence characteristics in the boundary layer. An improved stochastic model for particle transport and deposition in the turbulent boundary layer has been developed. The model considers the velocity, size and lifetime of eddies as random variables with appropriate distributions. The main features of the model are the inclusion of particle-eddy interactions and eddy decay. Results show the significance of interactions between particles and turbulence as well as eddy decay.;Particle rebound in the turbulent wall region has also been studied in the wind tunnel. Variations of the rebound percentage and the rebound flux with the particle diameter and the dimensionless particle relaxation time have been analyzed. Different particle rebound patterns are found in the developing boundary layer compared with those in the developed boundary layer due to differences in turbulence characteristics in the two regions. To explain the different rebound patterns, an improved energy balance model is proposed by applying the concepts of phase distinction and dynamic yield limit and coupled with the stochastic model for particle transport and deposition in the turbulent wall region. Results from numerical modeling explain the experimental findings.