A Numerical Investigation of Regional Fiber Deposition in a Realistic Nasal Cavity

2012 ◽  
Author(s):  
Alireza Dastan ◽  
Omid Abouali ◽  
Goodarz Ahmadi
Keyword(s):  
Nasal Cavity ◽  
Equations Of Motion ◽  
Computer Code ◽  
Spherical Particles ◽  
Navier Stokes ◽  
Continuity Equations ◽  
Aspect Ratios ◽  
Deposition Fraction ◽  
Fiber Deposition ◽  
Rotation Motion

In this paper, the motion and deposition of micro fibers in different regions of a realistic human nasal airway were studied using a computational modeling approach. The airflow field in the nasal cavity was simulated by solving the Navier-Stokes and continuity equations. The coupled translational and rotation motion of the fibers were analyzed by a Lagrangian approach assuming one-way coupling. The fibers were assumed to be ellipsoids and a computer code was developed for solving the coupled translational and rotational equations of motion of the ellipsoidal fiber. A large number of fibers were injected at the nostril and the deposition pattern and deposition fraction (DF) of the fibers in different regions of the nasal cavity were evaluated for different breathing rates, various fiber diameters and different fiber aspect ratios. The simulation results for ellipsoidal fibers obtained by solving the coupled translational and rotational equations were compared with those obtained by solving only the translational equations of equivalent spherical particles with a shape factor, which were used in some earlier works.

scholarly journals Airflow inside the nasal cavity: visualization using computational fluid dynamics

2010 ◽  
Vol 4 (4) ◽  
pp. 657-661 ◽  
Author(s):  
Mohammed Zubair ◽  
Vizy Nazira Riazuddin ◽  
Mohammed Zulkifly Abdullah ◽  
Rushdan Ismail ◽  
Ibrahim Lutfi Shuaib ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Nasal Cavity ◽  
Three Dimensional ◽  
Clinical Importance ◽  
Navier Stokes ◽  
Tomographic Images ◽  
Computed Tomographic ◽  
Continuity Equations ◽  
Cfd Method

Abstract Background: It is of clinical importance to examine the nasal cavity pre-operatively on surgical treatments. However, there is no simple and easy way to measure airflow in the nasal cavity. Objectives: Visualize the flow features inside the nasal cavity using computational fluid dynamics (CFD) method, and study the effect of different breathing rates on nasal function. Method: A three-dimensional nasal cavity model was reconstructed based on computed tomographic images of a healthy Malaysian adult nose. Navier-Stokes and continuity equations for steady airflow were solved numerically to examine the inspiratory nasal flow. Results: The flow resistance obtained varied from 0.026 to 0.124 Pa.s/mL at flow-rate from 7.5 L/min to 40 L/min. Flow rates by breathing had significant influence on airflow velocity and wall shear-stress in the vestibule and nasal valve region. Conclusion: Airflow simulations based on CFD is most useful for better understanding of flow phenomenon inside the nasal cavity.

Numerical Simulation of Airflow and Ellipsoidal Particle Deposition in Human Upper and Central Respiratory Tract

2019 ◽  
Author(s):  
Morteza Kiasadegh ◽  
Zahra Dehghani ◽  
Arash Naseri ◽  
Omid Abouali ◽  
Goodarz Ahmadi
Keyword(s):  
Respiratory Tract ◽  
Particle Deposition ◽  
Trajectory Analysis ◽  
Equations Of Motion ◽  
Particle Diameter ◽  
Discrete Phase Model ◽  
Ellipsoidal Particle ◽  
Constant Flow Rate ◽  
Continuity Equations ◽  
Aspect Ratios

Abstract Steady airflow pattern during a full breathing cycle in human upper and central respiratory tract was simulated by solving the Navier-Stokes and continuity equations. For ellipsoidal fiber trajectory analysis under cyclic breathing condition, several user defined functions (UDFs) were developed and coupled to the ANSYS-Fluent discrete phase model (DPM). The developed model accounted for solving the coupled translational and rotational equations of motion of ellipsoidal fibers. The airway passage model was extended from the vestibule to the fifth generation of the bronchial bifurcations obtained mostly from computed tomography (CT) scan. A constant flow rate of 15 L/min was used to simulate the normal breathing condition. The velocity and pressure fields for different regions of the respiratory track were evaluated and used for Lagrangian particle trajectory analysis. Total and regional depositions of each region for a range of ellipsoidal particle diameter and aspect ratios were evaluated and the results compared with the experimental data.

Deposition of Ellipsoidal Fibers in Nasal Cavity: Influence of Non-Creeping Flow Conditions

2019 ◽  
Author(s):  
Mehdi Aboulhasan Tash ◽  
Mohammad Mehdi Tavakol ◽  
Omid Abouali ◽  
Goodarz Ahmadi
Keyword(s):  
Nasal Cavity ◽  
Flow Condition ◽  
Hot Spot ◽  
Hydrodynamic Forces ◽  
Physical Activities ◽  
Creeping Flow ◽  
Airflow Rate ◽  
Ansys Fluent ◽  
Aspect Ratios ◽  
Deposition Fraction

Abstract In this study, deposition fraction of ellipsoidal particles in a 3D-Model of the nasal cavity (right airway) of a 24-year-old healthy woman was simulated for laminar and turbulent inhalation flow rates. The geometry used included the main nasal cavity from the nostril to the beginning of nasopharynx and was constructed in the Ansys-ICEM software from a CT scan image. The numerical simulations of governing equations were obtained using the Ansys-Fluent software. The mean airflow was assumed to be incompressible and steady. For turbulence modeling, the Realizable k-ε model was employed and the Lagrangian trajectory analysis method was used for particle tracking. For evaluating the ellipsoidal particle motions, several user-defined functions (UDFs) were developed and linked to the discrete phase model of the Ansys-Fluent code. The developed UDFs solve for the coupled translational and rotational equations of motion for ellipsoidal fibers and also accounts for the stochastic modeling of turbulence velocity fluctuations. The hydrodynamic forces and torques were calculated based on the non-creeping formulations for various ellipsoidal fibers. Laminar flow condition was assumed for breathing rate of 5.0 lit/min for the rest or light physical activities and turbulent flow condition was assumed for airflow rate of 20 lit/min for high physical activities. To investigate the dispersion and deposition of particles in the model of the human nasal cavity, various fibers with a semi-minor axis of 1, 3, 5 and 10 μm and various aspect ratios were considered. Using the non-creeping flow formulation for hydrodynamic forces and torques, the simulation results showed slight differences in the total deposition fraction of ellipsoidal fibers compared with the corresponding creeping flow model. Small fibers deposit roughly uniformly in the nasal cavity with no hotspot region. For the large inertial fibers, however, the nasal valve is a hot spot region, where the deposition rate reaches to its peak.

Detailed Analysis of Fiber Motion in Human Nasal Airways

2021 ◽  
Author(s):  
Jiang Li ◽  
J. W. Ma ◽  
J. Y. Tu ◽  
L. Tian ◽  
G. Ahmadi
Keyword(s):  
Experimental Data ◽  
Nasal Cavity ◽  
Particle Transport ◽  
Particle Deposition ◽  
Deposition Efficiency ◽  
Spherical Particles ◽  
Nasal Airways ◽  
Deposition Fraction ◽  
Simulation Results ◽  
Fiber Transport

Abstract Information on the fiber particle transport and deposition in human nasal airways is of great importance in inhalation toxicology study. Due to the complex interactions between the inhaled aerosol particles and human respiratory airways, the particles’ toxicity varies with their chemical composition, size, and shape. In the earlier computational study of fiber particle motion in human nasal cavities, overall deposition efficiency curves were evaluated and compared with the available experimental data. The majority of investigations were on micron-scale fiber particles, and the observed deposition fraction is strongly affected by fiber inertial impaction and the geometry of the cavity. The fiber characterization by its equivalent spheres is still not entirely fully understood. Limited existing evidence indicated that, when benchmarked by the impaction parameter, spherical particles tend to have a higher deposition fraction than that of the elongated fiber particles in the nasal cavity. More data is needed to elaborate on these observations and reveal the underlying physics. A more profound understanding of fiber transport in human airways may be obtained by comparing the fibrous particle deposition to that of the spherical particles. In this study, simulations of transport and deposition of elongated particles in a realistic human nasal cavity model for a steady laminar airflow rate were performed. FLUENT 19.2 was used to solve the airflow conditions. The elongated ellipsoidal particle transport and deposition were simulated using the coupled translational and rotational equations of motion. The hydrodynamic drag and torque, shear-induced lift, and gravitational force were included in the analysis. One-way coupling was assumed, and an in-house User Defined Function (UDF) was developed and was implemented into the ANSYS-FLUENT code for analyzing the fiber transport and deposition. The airflow field, the particle deposition efficiency, particle deposition pattern, and single-particle trajectories of fiber and sphere were analyzed and presented. The simulation results were compared with available experimental data and simulation results in the literature.

A series-expansion study of the Navier–Stokes equations with applications to three-dimensional separation patterns

1986 ◽  
Vol 173 ◽  
pp. 207-223 ◽  
Author(s):  
A. E. Perry ◽  
M. S. Chong
Keyword(s):  
Series Expansion ◽  
Arbitrary Order ◽  
Stokes Equations ◽  
Equations Of Motion ◽  
Three Dimensional ◽  
Taylor Series Expansion ◽  
Navier Stokes ◽  
Three Dimensional Flow ◽  
Navier Stokes Equations ◽  
Continuity Equations

An algorithm has been developed which enables local Taylor-series-expansion solutions of the Navier-Stokes and continuity equations to be generated to arbitrary order. Much of the necessary algebra for generating these solutions can be done on a computer. Various properties of the algorithm are investigated and checked by making comparisons with known solutions of the equations of motion. A method of synthesizing nonlinear viscous-flow patterns with certain required properties is developed and applied to the construction of a number of two- and three-dimensional flow-separation patterns. These patterns are asymptotically exact solutions of the equations of motion close to the origin of the expansion. The region where the truncated series solution satisfies the full equations of motion to within a specified accuracy can be found.

scholarly journals Simulation Analysis of Air Flow and Turbulence Statistics in a Rib Grit Roughened Duct

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
I. I. Vogiatzis ◽  
A. C. Denizopoulou ◽  
G. K. Ntinas ◽  
V. P. Fragos
Keyword(s):  
Heat Transfer ◽  
Simulation Analysis ◽  
Convective Heat Transfer Coefficient ◽  
Navier Stokes ◽  
Small Scale ◽  
Solar Air Heater ◽  
Turbulence Statistics ◽  
Continuity Equations ◽  
Aspect Ratios ◽  
The Impact

The implementation of variable artificial roughness patterns on a surface is an effective technique to enhance the rate of heat transfer to fluid flow in the ducts of solar air heaters. Different geometries of roughness elements investigated have demonstrated the pivotal role that vortices and associated turbulence have on the heat transfer characteristics of solar air heater ducts by increasing the convective heat transfer coefficient. In this paper we investigate the two-dimensional, turbulent, unsteady flow around rectangular ribs of variable aspect ratios by directly solving the transient Navier-Stokes and continuity equations using the finite elements method. Flow characteristics and several aspects of turbulent flow are presented and discussed including velocity components and statistics of turbulence. The results reveal the impact that different rib lengths have on the computed mean quantities and turbulence statistics of the flow. The computed turbulence parameters show a clear tendency to diminish downstream with increasing rib length. Furthermore, the applied numerical method is capable of capturing small-scale flow structures resulting from the direct solution of Navier-Stokes and continuity equations.

Numerical Simulation of Airflow and Ellipsoidal Particle Deposition in Human Upper Respiratory Tract

2018 ◽  
Author(s):  
Morteza Kiasadegh ◽  
Omid Abouali ◽  
Homayoun Emdad ◽  
Goodarz Ahmadi
Keyword(s):  
Particle Deposition ◽  
Equations Of Motion ◽  
Healthy Woman ◽  
Upper Airway ◽  
Realistic Model ◽  
Navier Stokes ◽  
Upper Respiratory Tract ◽  
Discrete Phase Model ◽  
Ansys Fluent ◽  
Continuity Equations

In this study, unsteady flow field and fibrous particle deposition in a realistic model of human upper airway system including vestibule to the end of trachea were investigated using the CFD technique. The airway passage model was constructed from the CT image of a 24 year old healthy woman. Unsteady airflow patterns during a full breathing cycle were simulated by solving the Navier-Stokes and continuity equations. For ellipsoidal fiber trajectory analysis under cyclic breathing condition, several user defined functions (UDFs) were coupled to the ANSYS-Fluent discrete phase model (DPM). The presented formulation accounted for solving the coupled translational and rotational equations of motion of ellipsoidal fibers. Total and regional depositions for a range of fiber sizes were evaluated. The transient particle deposition fraction was compared with those obtained from the equivalent steady flow condition. The presented results showed that the steady simulation can predict the total fibrous particle deposition during cyclic breathing with reasonable accuracy but cannot properly predict the regional deposition of particles.

The stability of unsteady axisymmetric incompressible pipe flow close to a piston. Part 1. Numerical analysis

1971 ◽  
Vol 50 (4) ◽  
pp. 625-644 ◽  
Author(s):  
J. H. Gerrard
Keyword(s):  
Stokes Equations ◽  
Equations Of Motion ◽  
Circular Cross Section ◽  
Cylindrical Tube ◽  
Navier Stokes ◽  
Ring Vortex ◽  
Random Disturbance ◽  
Time Step ◽  
Continuity Equations ◽  
Starting Flow

A numerical solution of the Navier-Stokes equations of motion by means of finite-difference forms of the vorticity and continuity equations is presented. This is applied to the study of the flow of an incompressible fluid produced by the motion from rest of a piston in a cylindrical tube of circular cross-section.Experiments at high Reynolds number indicated the presence in the starting flow of a ring vortex which was not reproduced by computation. Iteration to determine the stream function was not found to be necessary to achieve 1% accuracy. Omitting iteration is equivalent to only slightly disturbing the flow. An additional random disturbance applied to the flow at each time step was found to result in the production of the ring vortex.

scholarly journals Effect of an oscillating time-dependent pressure gradient on Dean flow: transient solution

2020 ◽  
Vol 9 (1) ◽  
Author(s):  
Basant K. Jha ◽  
Dauda Gambo
Keyword(s):  
Pressure Gradient ◽  
Initial Conditions ◽  
Fluid Velocity ◽  
Outer Cylinder ◽  
Time Dependent ◽  
Navier Stokes ◽  
Dean Flow ◽  
Continuity Equations ◽  
Riemann Sum ◽  
Flow Formation

Abstract Background Navier-Stokes and continuity equations are utilized to simulate fully developed laminar Dean flow with an oscillating time-dependent pressure gradient. These equations are solved analytically with the appropriate boundary and initial conditions in terms of Laplace domain and inverted to time domain using a numerical inversion technique known as Riemann-Sum Approximation (RSA). The flow is assumed to be triggered by the applied circumferential pressure gradient (azimuthal pressure gradient) and the oscillating time-dependent pressure gradient. The influence of the various flow parameters on the flow formation are depicted graphically. Comparisons with previously established result has been made as a limit case when the frequency of the oscillation is taken as 0 (ω = 0). Results It was revealed that maintaining the frequency of oscillation, the velocity and skin frictions can be made increasing functions of time. An increasing frequency of the oscillating time-dependent pressure gradient and relatively a small amount of time is desirable for a decreasing velocity and skin frictions. The fluid vorticity decreases with further distance towards the outer cylinder as time passes. Conclusion Findings confirm that increasing the frequency of oscillation weakens the fluid velocity and the drag on both walls of the cylinders.

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