Particle trajectory and deposition in contraction-expansion flow fields using coupled large eddy simulation and discrete phase model

Flow channel contractions and expansions often lead to flow separation and accelerated fouling deposition, particularly around the tube support plate (TSP) in steam generators. This study employed large eddy simulation (LES) coupled with the discrete phase model (DPM) to analyze deposition mechanisms at various locations within these flow configurations. Simulation results were compared with Reynolds-averaged Navier-Stokes (RANS) models, with LES showing superior predictive accuracy, especially when sub-grid-scale turbulence effects were considered. A comprehensive analysis of near-wall flow behavior, particle trajectories, and deposition characteristics was conducted. Results indicate that fouling deposition at the TSP inlet is particularly severe, with a high risk of blockage. A deposition model specific to the TSP inlet was developed, showing that dimensionless deposition velocity initially increases and then decreases with increasing dimensionless relaxation time. For tau(p)*<0.04, V-d(+) increases proportionally to (tau(p)*)(1.18). In contrast, for 0.04 <=tau(p)*<2.1, centrifugal forces reduce deposition, following V-d(+)proportional to(tau(p)*)(-0.77). This study advances the understanding of hard fouling formation and offers strategies for mitigation in steam generators and similar systems.