| Dispersed two-phase flows are abundant in nature and play an important role in a large number of engineering and environmental applications. In a Lagrangian--Eulerian modeling approach, the motion of particles in a carrier fluid is accounted for through force laws. In this thesis, our focus is to extend the current capability in predicting drag and lift forces on a particle, primarily when located near wall vicinity, and to gain a better understanding of the interactions between a particle and wall turbulence around a single particle in the context of finite particle Reynolds number. The investigations are performed through direct numerical simulation (DNS) using a highly accurate spectral element method.; Firstly, we study a finite-sized particle translating parallel to a wall in an otherwise stagnant fluid. This analysis addresses mainly the pure wall effect on the particle motion. The particle location is systematically varied from fairly close to the wall to sufficiently far away from the wall. The results show that lift coefficient follows a down-and-up behavior in contrast to the anticipated monotonically decreasing trend.; Secondly, we investigate a finite-sized particle in a wall-bounded linear shear flow. In addition to varying the particle location as in the previous part, we also present results for the case of a particle nearly sitting on the wall. Correlations for the lift and drag coefficients are proposed.; Thirdly, we investigate the interaction of a finite-sized particle embedded in a turbulent channel flow. Particles of various sizes have been located at two specific wall-normal locations, the buffer region and the channel center. Near-wall region mechanisms are observed consisting of such different events as bursting, sweep, and ejection, whereas channel center can be considered as nearly isotropic turbulence. We compare the computed forces with the standard force formulations and analyze possible mechanisms for their deviations. Further, we analyze the back effects that the particle imposes on the turbulence field---in particular, the wake responses to the ambient turbulence and the turbulence modulation by the particle for the energy and wall shear stress. |
