Effect of pollutant source location on air pollutant dispersion around a high-rise building.

This article investigates the dispersion of airborne pollutants emitted from different locations near a high-rise building. A Computational Fluid Dynamics (CFD) model for simulating the wind flow field and the pollutant dispersion was developed and validated by wind tunnel data. Then the spreading of the pollutant emitted from different locations to a rectangular-shaped high-rise residential (HRR) building was numerically studied. The pollutant source location was set in a wide range of the position angle and distance between the source and the building. It was found that the pollutant concentration on the building decreases with an increase in the emission distance whereas the effect of the position angle is more complicated. Interestingly, there is a critical range of the position angle from which the emitted pollutants will not spread to the building in a significant way. The effect of the source location was linked to the wind flow field around the building, particularly with several major flows. The vertical distributions of the pollutant concentration on different faces were also investigated, and it was found that these are more affected by the vertical flow near each face. Finally, a mathematical model was developed to evaluate the pollutant concentration as a function of the emission distance and position angle. These findings are helpful to the understanding of the dispersion of airborne pollutants around high-rise buildings and the related hazard management in urban design.

Numerical investigation of the flow field in realistic nasal septal perforation geometry.

The computational fluid dynamics (CFD) are used to evaluate the physiological function of the nose. We evaluated the aerodynamics of the nasal cavity in a patient with septal perforation (SP), pre- and postvirtual repair. Three-dimensional nasal models were reconstructed, and then a wide range of the pressure drops and flow rates were analyzed. The airflow velocity is higher in the central region and is lower around the boundary of the SP. The air velocity in the SP increases as the pressure drop increases. Furthermore, at the anterior part of the SP, the shear stress is higher in the upper part. In addition, the repair of SP does not affect the total nasal airflow rate and the velocity contour patterns. The potential usage of the CFD technique as a predictive technique to explore the details and a preoperative assessment tool to help in clinical decision making in nasal surgery is emphasized.

Micro and nanoparticle deposition in human nasal passage pre and post virtual maxillary sinus endoscopic surgery.

Realistic 3-D models of the human nasal passages were developed pre and post virtual uncinectomy and Middle Meatal Antrostomy. A 3-D computational domain was constructed by a series of coronal CT scan images from a healthy subject. Then a virtual uncinectomy intervention and maxillary antrostomy were performed on the left nasal passage by removing the uncinate process and exposing the maxillary sinus antrum. For several breathing rates corresponding to low or moderate activities, the airflows in the nasal passages were simulated numerically pre and post virtual routine maxillary sinus endoscopic surgery. The airflow distribution in the nasal airway, maxillary and frontal sinuses were analyzed and compared between pre and post surgery cases. A Lagrangian trajectory analysis approach was used for evaluating the path and deposition of microparticles in the nasal passages and maxillary sinuses. A diffusion model was used for nanoparticle transport and deposition analysis. The deposition rate of the inhaled micro and nanoparticles in the sinuses were evaluated and compared for pre and post operation conditions. The results showed that after maxillary sinus endoscopic surgery, the inhaled nano and microparticles can easily enter this sinus due to penetration of the airflow into the sinus cavity. This was in contrast to the preoperative condition in which almost no particles entered the sinuses. These results could be of importance for a better understanding of the effect of sinus endoscopic surgery on patient exposure to particulate pollution and inhalation drug delivery. The significantly higher airflow rate and particle deposition in the sinus could be a reason for the discomfort reported by some patient after maxillary sinus endoscopic surgery.

Numerical analysis of micro- and nano-particle deposition in a realistic human upper airway.

A computational model was developed for studying the flow field and particle deposition in a human upper airway system, including: nasal cavity, nasopharynx, oropharynx, larynx and trachea. A series of coronal CT scan images of a 24 year old woman was used to construct the 3D model. The Lagrangian and Eulerian approaches were used, respectively, to find the trajectories of micro-particles and concentration of nano-particles. The total and regional deposition fractions of micro/nanoparticles were evaluated and the major hot spots for the deposition of inhaled particles were found.