Shahab Taherian

CFD Modeling and Analysis of Pulmonary Airways/Particles Transport and Deposition

Unsteady numerical simulations of air flow, mixed with micron particles, through a human lung conducting zone during inhalation have been performed. The process included importing images from a high resolution CT-Scan into a CFD software, generation of the CFD model and then CFD simulation over a 4 seconds cycle (2 seconds for inhalation and 2 seconds for exhalation). The inlet diameter was 11 mm and the flow rates were 5, 7.5, and 15 liters/ min. Only results for the highest flow rate are presented. The implicit-unsteady Reynolds Average Navier-Stokes equations with the Wilcox K-ω turbulence model were used for the simulation. The micron particles were solid round coal with 1000 Kg/m 3 density. Results indicate high correlation between regions of high vorticity and secondary flow and particle deposits. This was mostly evident in the main bronchus. While most particles should exit the lung during the exhalation process, however, areas of recirculating flow and near the walls continue to have some particle deposits.

Tracheal Stenosis: A CFD Approach for Evaluation of Drug Delivery

The existence of obstructions such as tracheal stenosis has major impacts on respiratory functions. Therapeutic effectiveness of inhaled medications is influenced by tracheal stenosis, and particle transport and deposition pattern are modified. The majority of studies have focused on obstructions in branches of the airways, where the flow is diverted to the other branches to meet the needed oxygen intake. In this study we have investigated the effects of trachea with and without stenosis/obstruction on particle depositions and air flow in a human respiratory system. Patient specific CFD simulations were conducted; CT-scans of a patient with tracheal stenosis were used to create 3D models of bronchial tree up to 8 generations. The section of the stenosis was manually modified to create a healthy trachea. Comparisons between CFD simulations before and after intervention demonstrate the impact of the stenosis on flow characteristics and particles distribution. The numerical investigations were performed using the implicit Unsteady Reynolds-Averaged Navier-Stokes equation (U-RANS), using the commercially available software (STAR-CCM+) from CD-Adapco, along with K-ω; shear stress transport model. Two sets of CT-images of inhalation and exhalation were used for assigning Patient-specific boundary conditions at the outlets. Lagrangian Phase model was used to simulate particle transport and depositions of 10, 5 and 2.5 micron diameter particles. Results of the particle depositions for 10 micron particles highlight the difference in depositions and ultimately inhaled medications in patients with and without tracheal stenosis. Particle deposition for normal Tidal volume increased due to stenosis from 47% to 51% for 10 Micron particles and not a significant change for the 2.5 Micron particles (from 4.5% to 4.7%).Comparisons of pressure drop in each generation between patient with tracheal stenosis and the healthy lung showed significant increase in pressure drop after the stenosis, which were experienced in all generations downstream. Experimental validation of the CFD results were made with a model of healthy trachea up to 3rd generation, manufactured using Additive Layer Manufacturing (ALM) from CT-images and pressure results were compared with the corresponding CFD results. Good agreements were found.Copyright

Particulates Depositions in Patient-Specific Simulations of Respiratory System

Ambient particulates depositions have major impacts on respiratory functions. Patient-specific simulations of the respiratory system of a patient were performed to investigate the relationship between the flow characteristics and particulate depositions in the upper respiratory domain. CT scan images were imported to create a 3D model of the bronchial tree and then transferred to a computational fluid dynamics (CFD) software for simulation. Appropriate boundary conditions were assigned to simulate the sinusoidal behavior of the normal breathing cycle with the corresponding pressures at the outlets. Lagrangian phase model was used to simulate the micron solid round particulates transport and depositions. The simulations were performed for 2.5 micron and 10 micron particles. The implicit-unsteady Reynolds Averaged Navier-Stokes equations with K-ω turbulence model were used for these simulations. Results indicate high correlation between regions of high vortices, secondary flow and high wall shear stress and particulate depositions. The total deposition number for 10-micron particles was higher than that for the 2.5-micron particles. The differences in the locations of depositions at various generations of the lung illustrate the importance of the patient-specific simulations.Copyright

PARTICULATE DEPOSITION IN A PATIENT WITH TRACHEAL STENOSIS

The presence of obstructions such as tracheal stenosis has important effects on respiratory functions. Tracheal stenosis impacts the therapeutic efficacy of inhaled medications as a result of alterations in particle transport and deposition pattern. This study explores the effects of the presence and absence of stenosis/obstruction in the trachea on air flow characteristics and particle depositions. Computational fluid dynamics (CFD) simulations were performed on three-dimensional (3D) patient-specific models created from computed tomography (CT) images. The analyzed model was generated from a subject with tracheal stenosis and includes the airway tree up to eight generations. CT scans of expiratory and inspiratory phases were used for patient-specific boundary conditions. Preand post-intervention CFD simulations’ comparison reveals the effect of the stenosis on the characteristics of air flow, transport, and depositions of particles with diameters of 1, 2.5, 4, 6, 8, and 10 lm. Results indicate that the existence of the stenosis inflicts a major pressure force on the flow of inhaled air, leading to an increased deposition of particles both above and below the stenosis. Comparisons of the decrease in pressure in each generation between preand post-tracheal stenosis intervention demonstrated a significant reduction in pressure following the stenosis, which was maintained in all downstream generations. Good agreements were found using experimental validation of CFD findings with a model of the control subject up to the third generation, constructed via additive layer manufacturing from CT images. [DOI: 10.1115/1.4038260]

Computational fluid dynamics evaluation of excessive dynamic airway collapse

Background: Excessive dynamic airway collapse, which is often caused by the collapse of the posterior membrane wall during exhalation, is often misdiagnosed with other diseases; stents can provide support for the collapsing airways. The standard pulmonary function tests do not necessarily show change in functional breathing condition for evaluation of these type of diseases. Methods: Flow characteristics through a patients airways with excessive dynamic airway collapse have been numerically investigated. A stent was placed to support the collapsing airway and to improve breathing conditions. Computed tomography images of the patients pre‐ and post‐stenting were used for generating 3‐Dimensional models of the airways, and were imported into a computational fluid dynamics software for simulation of realistic air flow behavior. Unsteady simulations of the inspiratory phase and expiratory phase were performed with patient‐specific boundary conditions for pre‐ and post‐intervention cases to investigate the effect of stent placement on flow characteristic and possible improvements. Findings: Results of post‐stent condition show reduced pressure, velocity magnitude and wall shear stress during expiration. The variation in wall shear stress, velocity magnitude and pressure drop is negligible during inspiration. Interpretation: Although Spirometry tests do not show significant improvements, computational fluid dynamics results show significant improvements in pre‐ and post‐treatment results, suggesting improvement in breathing condition. HighlightsInspiratory‐expiratory CT‐based models were used for patient‐specific simulations.Spirometry results do not necessarily show symptom improvement post‐intervention.Fluid simulations show significant improvements in airflow and functional breathing.Post‐stent results show reduced pressure and velocity magnitude during expiration.

Effects of Nasal Cavity and Pharyngeal Regions on Airflow Simulation and Particle Depositions in Lower Generations of the Airways

This study evaluates the impact of excluding various regions of the upper respiratory system on particle depositions in lower airways. Three types of models were investigated, Type 1 includes nasal cavity, pharyngeal regions, trachea, and lower generations, Type 2 includes pharyngeal regions, trachea and lower generations, and finally Type 3 includes just the trachea and lower generations. Results indicate increased mean velocity, turbulent kinetic energy, and wall shear stress in hypopharynx and trachea regions for Types 1 and 2 models. There are strong secondary flows within the trachea just before the lower generations in these models, moving high velocity toward the wall regions, resulting in large velocity gradients and thus increased wall shear stress. For Type 3 model, only a small region experiences high velocity secondary flow and its distribution is significantly different than those of Type 1 and 2. Although total particle depositions differ between models, results show that for fine particles, the deposition ratios in lower airways are nearly the same.Copyright

Virus Transport Aboard Commercial Regional Aircraft

Air ventilation systems in aircraft cabins are used to create a comfortable environment for travelling passengers. However, droplets exhaled by passengers with infectious diseases have a potential to affect and contaminate other passengers. The present study is the first part of several ongoing investigations at CEERS on indoor air quality and health aboard public transportation systems with the present investigations focused on a commercial regional aircraft. The investigation is on droplet (virus) transport and dispersion. Unsteady simulations of air movement within a commercial regional aircraft using a commercial Computational Fluid Dynamics (CFD) software are presented. Unsteady release of particles in the size of cold viruses from passengers seated at different locations in the form of coughing are assumed. Results for duration of 120 seconds, which include contours of mean velocity, droplet velocity, temperature and droplet count, show that the ventilation system and characteristics of the airflow have significant effects on the virus/droplet dispersion. For this study, the air supply within the cabin was through axial ceiling exhaust slots running parallel with the aisle. The air recirculation rapidly disperses the droplets released to the front and rear rows, while preventing the dispersion of the droplets to the other side of the aisle.