Tevfik Gemci

Bio: Tevfik Gemci is an academic researcher from Carnegie Mellon University. The author has contributed to research in topics: Airflow & Particle. The author has an hindex of 11, co-authored 18 publications receiving 480 citations. Previous affiliations of Tevfik Gemci include University of Nevada, Las Vegas & Sakarya University.

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

Abstract: An inhalation airflow 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 airflow using a jet nebulizer. Measurements of axial veloci...

Computational simulations of airflow in an in vitro model of the pediatric upper airways.

Abstract: In order to understand mechanisms of gas and aerosol transport in the human respiratory system airflow in the upper airways of a pediatric subject (male aged 5) was calculated using Computational Fluid Dynamic techniques. An in vitro reconstruction of the subject's anatomy was produced from MRI images. Flow fields were solved for steady inhalation at 6.4 and 8 LPM. For validation of the numerical solution, airflow in an adult cadaver based trachea was solved using identical numerical methods. Comparisons were made between experimental results and computational data of the adult model to determine solution validity. It was found that numerical simulations can provide an accurate representation of axial velocities and turbulence intensity. Data on flow resistance, axial velocities, secondary velocity vectors, and turbulent kinetic energy are presented for the pediatric case. Turbulent kinetic energy and axial velocities were heavily dependant on flow rate, whereas turbulence intensity varied less over the flow rates studied. The laryngeal jet from an adult model was compared to the laryngeal jet in the pediatric model based on Tracheal Reynolds number. The pediatric case indicated that children show axial velocities in the laryngeal jet comparable to adults, who have much higher tracheal Reynolds numbers than children due to larger characteristic dimensions. The intensity of turbulence follows a similar trend, with higher turbulent kinetic energy levels in the pediatric model than would be expected from measurements in adults at similar tracheal Reynolds numbers. There was reasonable agreement between the location of flow structures between adults and children, suggesting that an unknown length scale correlation factor could exist that would produce acceptable predictions of pediatric velocimetry based off of adult data sets. A combined scale for turbulent intensity as well may not exist due to the complex nature of turbulence production and dissipation.

Challenges Facing Future Micro-Air-Vehicle Development

Abstract: Nomenclature Ar = rotor disk area CD = sectional drag coefficient CD0 = zero-lift drag coefficient Clα = lift-curve slope CP = power coefficient CPi = induced power coefficient CP0 = profile power coefficient CT = thrust coefficient c = chord length D = drag force D.L . = disk loading L = lift force m = mass P.L . = power loading SF = separated flow T = rotor thrust V = local wind velocity perceived by flap W = weight W f = final weight Wo = gross takeoff weight α = blade section angle of attack η = efficiency μ = dynamic viscosity ρ = air density σ = rotor solidity = flapping amplitude (peak to peak)

Airflow and Particle Transport in the Human Respiratory System

Abstract: Airflows in the nasal cavities and oral airways are rather complex, possibly featuring a transition to turbulent jet-like flow, recirculating flow, Dean's flow, vortical flows, large pressure drops, prevailing secondary flows, and merging streams in the case of exhalation. Such complex flows propagate subsequently into the tracheobronchial airways. The underlying assumptions for particle transport and deposition are that the aerosols are spherical, noninteracting, and monodisperse and deposit upon contact with the airway surface. Such dilute particle suspensions are typically modeled with the Euler-Lagrange approach for micron particles and in the Euler-Euler framework for nanoparticles. Micron particles deposit nonuniformly with very high concentrations at some local sites (e.g., carinal ridges of large bronchial airways). In contrast, nanomaterial almost coats the airway surfaces, which has implications of detrimental health effects in the case of inhaled toxic nanoparticles. Geometric airway features, ...