Simulation of particles released near the wall in a turbulent boundary layer |
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Affiliation: | 1. School of Economics and Business Administration, Chongqing University, Chongqing, 400044, China;2. School of Economics, Guizhou University, Guiyang, 550025, China;1. School of Public Policy and Administration, Chongqing University, Chongqing, China;2. College of Economics and Management, Northwest Agriculture and Forestry University, Yangling, China;3. University of Orleans, France;4. Inistute of Business &Management, University of Engineering and Technology, Pakistan;5. Faculty of Agricultural Social Sciences, Sindh Agriculture University Tandojam, Pakistan;1. School of Metallurgical Engineering, Anhui University of Technology, Maanshan 243002, Anhui Province, PR China;2. College of Material Science and Engineering, Chongqing University, Chongqing 400030, PR China;3. School of Metallurgy, Northeastern University, Shengyang 110819, Liaoning Province, PR China;4. College of Metallurgy and Energy, North China University of Science and Technology, Tangshan 063009, PR China |
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Abstract: | A direct numerical simulation was used along with a Lagrangian particle tracking technique to study particle motion in a horizontal, spatially developing turbulent boundary layer along an upper-wall (with terminal velocity directed away from the wall). The objective of the research was to study particle diffusion, dispersion, reflection, and mean velocity in the context of two parametric studies: one investigated the effect of the drift parameter (the ratio of particle terminal velocity to fluid friction velocity) for a fixed and finite particle inertia, and the second varied the drift parameter and particle inertia by the same amount (i.e. for a constant Froude number). A range of drift parameters from 10−4 to 100 were considered for both cases. The particles were injected into the simulation at a height of four wall units for several evenly distributed points across the span and a perfectly elastic wall collision was specified at one wall unit.Statistics collected along the particle trajectories demonstrated a transition in particle movement from one that is dominated by diffusion to one that is dominated by gravity. For small and intermediate sized particles (i.e. ones with outer Stokes numbers and drift parameters much less than unity) transverse diffusion away from the wall dominated particle motion. However, preferential concentration is seen near the wall for intermediate-sized particles due to inhomogeneous turbulence effects (turbophoresis), consistent with previous channel flow studies. Particle–wall collision statistics indicated that impact velocities tended to increase with increasing terminal velocity for small and moderate inertias, after which initial conditions become important. Finally, high relative velocity fluctuations (compared to terminal velocity) were found as particle inertia increased, and were well described with a quasi-one-dimensional fluctuation model. |
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