A Numerical and Experimental Study of Spray Dynamics in a Simple Throat Model

Abstract

An inhalation air ow through a simple model of the human larynx and trachea, containing dispersed drug spray droplets, is studied numerically using the Computational Fluid Dynamics (CFD) code KIVA-3V (Amsden 1997) and experimentally using phase doppler interferometry. Flow conditions within the larynx and trachea affect the delivery of inhaled medications to the lungs. Deposition in these regions is considered undesirable and has been shown to be a particular problem for pediatric patients. The larynx geometry is represented by a constricted portion inside a straight tube. This constriction simulates the vocal folds within the larynx. The experimental model was 3.2 cm in diameter (approximately twice human scale) and 90 cm long. The constriction was 0.7 cm thick and was placed 30 cm from the inlet of the tube. The area of the constricted opening is approximately 40% of the tube area. Water droplets are introduced into the low-turbulence upstream air ow using a jet nebulizer. Measurements of axial velocity and axial turbulence intensity were made through an array of points between 2 diameters upstream and 4 diameters downstream of the constriction. Steady ows were used and the ow rates scaled to match in vivo tracheal Reynolds numbers simulating two different breathing conditions. The KIVA-3V code is speci cally designed to analyze transient, two-and three-dimensional, chemically reactive uid ows with sprays. The analysis considers spray dynamic effects such as coalescence, evaporation, deposition, and turbulent dispersion. The numeric simulation is carried out in a model consisting of a 21.7 cm long pipe simulating the measurement region. All other dimensions are identical to the experimental model. Several signi cant spray deposition mechanisms were notable in both the experimental and the numerical results.

Steady flow through a realistic human upper airway geometry

“…The majority of applications in the literature concentrate around the topic of particle transport in upper and lower human airways. Studies on this topic include application to spray dynamics and smoke particles [36][37][38][39][40][41][42][43][44][45][46]. In these studies, in addition to a fluid dynamics algorithm, an efficient way of tracking the particles is essential.…”

Influence of the spray retroaction on the airflow

“…The situations we deal with in this work are only two-dimensional, but the model also holds for three dimensions [4,6,9,17]. The airflow can be described by its velocity field u(t, x) ∈ R 2 and the pressure p(t, x) ∈ R, where t ≥ 0 is the time and x = (x 1 , x 2 ) ∈ R 2 is the space location.…”

“…When this solution is disturbed, the pressure boundary conditions are modified by taking into account the quantity ν ∂u/∂n − p n instead of p only. The fluid is set with the initial condition on u and p given by (9). The spray induces a perturbation of the fluid Poiseuille profile.…”

“…Conversely, one can very often find in the literature that the so-called retroaction of the spray on the air is neglected, see [7,13] for instance. It is not neglected in [9], in the model as well as in the computations. This work aims to quantify this statement, as it was not investigated yet, up to our knowledge.…”

Research of transport and deposition of aerosol in human airway replica

“…Their results showed that the secondary velocity depends not only on the branching angle and curvature of the tube, but very strongly on the shape of the previous branching. [7] and later Gemci et al [9]. Measurements were conducted on a glass cylinder, which contained a triangular slot as a simulation of vocal cords.…”