Revision as of 10:13, 2 October 2019

Aerosol deposition in the human upper airways

Application Challenge AC7-01 © copyright ERCOFTAC 2019

Description

Introduction

The objective of the current application Challenge is to present a benchmark case that can be used for the validation of computational tools intended for regional deposition studies in the upper airways. In the present application Challenge, in vitro deposition measurements in a complex realistic geometry are provided at various inhalation ﬂow rates. CFD results are then compared against the measured data. Since deposition in the upper airways is determined by the airﬂow features, a second application Challenge will follow where airﬂow measurements using Particle Image Velocimetry (PIV) are reported in the same geometry. These will again be compared against the LES and RANS predictions. In this manner, a complete benchmark case for the validation of computational packages intended for deposition predictions in the upper airways will be established and made available to the wider community. Furthermore, best practice guidelines for numerical predictions of regional deposition in the airways, which can assist in the design and optimization of inhalation therapies, will be provided.

In the current application Challenge, the in vitro deposition measurements have been conducted in a human—based model of the upper airways, shown in ﬁgure 3, using positron emission tomography (PET). The experiments were performed at steady—state inhalation with ﬂow rates of 15, 30 and 60 L/min. The ﬂow conditions at these ﬂowrates are in the transitional to turbulent regime. The CFD simulations were carried out in the same geom— etry and under the same ventilation conditions. Two sets of simulations were performed: Large Eddy Simulations using the dynamic version of the Smagorinsky-Lilly subgrid scale model and RANS simulations using the k-ω-SST model. In both methods, the Lagrangian approach has been adopted to track spherical particles in the airway geometry and determine regional deposition patterns. The methods and results described in the present Application Challenge are mainly adopted from Lizal et al. (2012) (experimental part) and Koullapis et al. (2018) (numerical part)

Relevance to Industrial Sector

Aerosolized delivery of drugs to the lungs is used to treat a number of respiratory diseases. Regional deposition effects play a critical role in applications where targeted drug delivery is needed in order to maximize efﬁcacy and minimize side-effects. Quantifying regional deposition is therefore important in assessing and optimizing treatment. Validated computational ﬂuid-particle dynamics (CFPD) methods offer a powerful tool to predict airﬂow and localized deposition in the respiratory airways, in order to further our understanding of the ﬂow and aerosol dynamics, and test and optimize inhaler therapies. However, accurate and efﬁcient numerical simulations of the respiratory airways pose a Challenge due to the complexities associated with the airway geometry, the ﬂow dynamics and the aerosol physics. Numerical studies conducted to date have adopted a variety of computational techniques, a range of airway geometries varying in complexity, and differing assumptions on the ﬂow and aerosol physics. In addition to the wide variability in the modelling approaches, validation of CFPD methods in the respiratory airways is limited.

Design or Assessment Parameters

Deposition fractions (DF) in the various segments of the geometry were measured (in the experiments) and predicted in the numerical simulations. The procedure to calculate DF in the PET experiments is described in section 2.3. DF in the simulations, where particles are tracked individually, are simply deﬁned as the ratio of the number of deposited particles in a segment to the total number of particles injected in the model.

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