Large Eddy Simulations of Particle Dispersion and Deposition in a Turbulent Square Duct Flow

In the current dissertation work, the preferential concentration and deposition of heavy solid particles in a downward, fully developed turbulent square duct flow are studied using large eddy simulations. A second-order accurate, finite-volume based fractional step scheme, based on an unstructured Cartesian mesh, is used to integrate the unsteady, incompressible, three-dimensional Navier-Stokes equations. An algebraic multigrid solver is used to solve the Poisson equation resulting from the fractional step method. The subgrid stresses are modeled with a dynamic subgrid kinetic energy model. The particle equation of motion includes drag, lift and gravity forces and is integrated using the fourth-order accurate Runge-Kutta method. The Reynolds number for the square duct is 360, based on average friction velocity and duct width. The grid used is 80×80×128 in the two wall-normal and streamwise directions, respectively. The preferential concentration of particles is studied assuming that the particles do not modify the turbulence and that particle-particle collisions are insignificant. The continuous and the dispersed phases are treated using Eulerian and Lagrangian approaches, respectively. Four cross-sectional locations representative of the time mean secondary flow patterns and six particle response times were chosen to study the effect of location and particle inertia on preferential concentration. Variation of vorticity magnitude, swirling strength, strain-rate, and ∇u:∇u, and their probability distribution functions(PDF), with particle response time and location is shown to demonstrate preferential concentration. Particles are seen to accumulate in regions of high ∇u:∇u and strain-rate and in regions of low swirling strength. In general, particles accumulate in regions of low vorticity magnitude. However, near the wall, large particles accumulate in regions of high vorticity magnitude. In addition, instantaneous contours of the above statistics and scatter plots of particle positions in a near-wall plane are presented to illustrate preferential concentration. Deposition of particles in a square duct is the focus of the second set of simulations. Ten particle response times are studied. Simulations are carried out using one-way coupling as well as select cases using twoand fourway coupling. A particle -particle collision algorithm has been developed. PDFs of deposition location, average streamwise and wall-normal deposition velocities, and deposition rates are presented.