Prediction of aerosol deposition in 90 bends using LES and an efficient Lagrangian tracking method

Aiming at the better prediction of pharmaceutical aerosol deposition in extrathoracic airways, a simpler test case, namely a 90 bend flow (tubular cross-section) laden with monodisperse particles, is adopted here and studied numerically. The continuous phase is calculated using a large-eddy simulation technique along with a finite-volume method for block-structured curvilinear grids. The particulate phase is simulated using a Lagrangian approach where hundred thousands of individual monodisperse particles with varying particle diameters are released and tracked throughout the computational domain. To allow such a large number of particles, a highly efficient tracking algorithm is applied, where particle paths are predicted in an orthogonal computational domain, avoiding time-consuming search algorithm, normally required when particles are tracked in the actual physical domain of a curvilinear body-fitted block-structured grid. Both simulation algorithms, for the continuous and particulate phases, are completely parallelized using domain decomposition. Additionally, the in-house code applied supports vector processing allowing efficient usage of nearly all kinds of high-performance architectures. Two different Reynolds numbers ReD are considered where ReD is based on the bend diameter and mean flow velocity. The first case is within the laminar regime at ReD=1000 and serves for the purpose of verification and validation. The second, more challenging case comprises the turbulent regime at ReD=10,000, which is the intrinsic objective of the present study. Depending on the Stokes number of the particles, 0.001 St 1.5, and the releasing locations at the entrance of the bend, the particles will either deposit on the wall or penetrate and exit the computational domain. Simulation results of aerosol deposition efficiency, over the entire range of particle diameters considered here, show an excellent agreement when compared to experimental values obtained by Pui, Romay-Novas, and Liu [(1987). Experimental study of particle deposition in bends of circular cross-section. Aerosol Science and Technology, 7, 301].