Euler–Lagrange simulation of gas–solid pipe flow with smooth and rough wall boundary conditions

Numerical simulation of upward turbulent particle-laden pipe flow is performed with the intention to reveal the influence of surface roughness on the velocity statistics of the particle phase. A rough wall collision model, which models the surface as being sinusoidal, is proposed to account for the wall boundary condition ranging for smooth surfaces to very rough surfaces. This model accounts for the entire range of possible surface roughness found in pipes and industrial pneumatic equipment from smooth plastic pipes over machined steel pipes to cast iron surfaces. The model is based on a geometric interpretation of the wall collision process where the particle restitution coefficient is based on the data presented by Sommerfeld and Huber [1]. Simulations are performed using the Eulerian–Lagrangian methodology for the dilute one-way coupling regime. Results are reported for 3 different sizes of glass spheres: 50 μm, 200 μm and 550 μm and evaluated using the data by Mathisen et al. [2]. The results reveal the dependence of the particle concentration, particle mean and particle RMS velocity profiles on the surface roughness. Significant differences can be seen for the particle RMS velocity profiles as the mean motion changes from motion mainly in the axial direction for the smooth surface condition to bouncing motion between the pipe sides for the fully rough surface condition.

Numerical simulations for upward particle laden flow have been performed in order to extract statistical data for the particle phase for different particle sizes and surface roughness. Results show that particle RMS velocities are greatly enhanced and the entrance length is significantly longer if particle statistics is considered.Figure optionsDownload as PowerPoint slideHighlights
► A new model for wall collisions with rough wall boundary conditions is proposed.
► We examine the influence of particle size and wall BC on the entrance length.
► Particle statistics with emphasis on Particle RMS velocity is gathered.
► It is found that rough surfaces greatly increase the particles RMS velocity.
► Also, the mean axial velocity at the centerline was decreased for rough wall BC.