Computational fluid dynamics (CFD) simulations of aerosol in a u-shaped steam generator tube

摘要

To quantify primary side aerosol retention, an Eulerian/Lagrangian approach wasused to investigate aerosol transport in a compressible, turbulent, adiabatic, internal,wall-bounded flow. The ARTIST experimental project (Phase I) served as the physicalmodel replicated for numerical simulation. Realizable k-? and standard k-? turbulencemodels were selected from the computational fluid dynamics (CFD) code, FLUENT, toprovide the Eulerian description of the gaseous phase.Flow field simulation results exhibited: a) onset of weak secondary flowaccelerated at bend entrance towards the inner wall; b) flow separation zonedevelopment on the convex wall that persisted from the point of onset; c) centrifugalforce concentrated high velocity flow in the direction of the concave wall; d) formationof vortices throughout the flow domain resulted from rotational (Dean-type) flow; e)weakened secondary flow assisted the formation of twin vortices in the outflow crosssection; and f) perturbations induced by the bend influenced flow recovery several pipe diameters upstream of the bend. These observations were consistent with those ofprevious investigators.The Lagrangian discrete random walk model, with and without turbulentdispersion, simulated the dispersed phase behavior, incorrectly. Accurate depositionpredictions in wall-bounded flow require modification of the Eddy Impaction Model(EIM). Thus, to circumvent shortcomings of the EIM, the Lagrangian time scale waschanged to a wall function and the root-mean-square (RMS) fluctuating velocities weremodified to account for the strong anisotropic nature of flow in the immediate vicinity ofthe wall (boundary layer). Subsequent computed trajectories suggest a precision thatranges from 0.1% to 0.7%, statistical sampling error. The aerodynamic mass mediandiameter (AMMD) at the inlet (5.5 ?m) was consistent with the ARTIST experimentalfindings. The geometric standard deviation (GSD) varied depending on the scenarioevaluated but ranged from 1.61 to 3.2. At the outlet, the computed AMMD (1.9 ?m) hadGSD between 1.12 and 2.76. Decontamination factors (DF), computed based ondeposition from trajectory calculations, were just over 3.5 for the bend and 4.4 at theoutlet. Computed DFs were consistent with expert elicitation cited in NUREG-1150 foraerosol retention in steam generators.