1. Investigation of Flow in a Model of Human Respiratory Tract
using PIV technique
Nguyen Lu Phuong and Kazuhide Ito
Interdisciplinary Graduate School of Engineering Sciences (IGSES), Kyushu University, Japan
1) Idealized model
2) Realistic model
Fig 4. Plots of two dimensional mean velocity vectors in central sagittal plane.
Otherwise, Figure 4(2) prove remarkable phenomenon of inclination of the flow to the anterior side of the trachea. Because of centrifugal force induced pressure gradient, the secondary motion of the fluid persisted in the posterior side when the airflow turned the bent from the upstream to downstream. Moving further to downstream of trachea region, the flow fields become well develops.
Fig 1. Schematic representation of the in vitro experimental set-up for PIV measurement
Introduction
An investigation of air flow patterns will provide essential information to reveal how particles transported and deposited in the human respiratory tract. In this study, we conduct in vitro experiment to investigate the flow pattern in the idealized- and realistic- geometry of a human airway.
Validation between PIV and CFD data u+
Idealized model
Realistic model
Fig 3. The in vitro model prototypes.
Objective
The working fluid condition in this experiment should have the same Reynolds number (Re) in both the numerical simulations and the experimental measurements. The relationship is given as follows:
where Qmixture is the volumetric flow rate and ν, the kinematic viscosity. The Reynolds number for steady flow measurement was ~500 in this experiment.
The in vitro experimental data is used to validate with computational fluid dynamics (CFD) results.
1) PIV data
2) CFD predictions
Experimental Methods
Fig 5. Contour of normalized two-component velocity magnitude u+ in central sagittal plane.
Prototype Model Creation
The computational realistic model was reproduced from CT data of a real human airway. The computational idealized model was simplified but constructed based on a realistic human airway model.
Figure 5(1) and (2) shows velocity magnitude u+=u/uin with obtained by PIV and CFD, respectively. Velocity profiles in the trachea in both experiment and simulation were identified. The maximum simulated velocity found in the downstream smaller than experimental data. Overall, experimental data agree well with CFD predictions.
Particle Image Velocimetry (PIV) technique
A two-dimensional flow field was measured using hollow glass spheres (60 µm) as tracers for visualization. Tracer particle motions were captured using a high-speed Photron FASTCAM APX camera recording on a complementary metal-oxide-semiconductor (CMOS) sensor. The frame rate was basically fps with a resolution of 512 × 1,024 pixels. A continuous wave (CW) laser (Beamtech Optronics, diode-pumped solid state (DPSS) green laser, 2 W, 532-nm wavelength) was used as a light source. The field of view of the CMOS camera could resolve a region of 26 mm × 52 mm by illuminating a light sheet of ~1-mm thickness discharged from the laser.
Three-dimensional printer was employed to produce the realistic and idealized replica from the computational model. A prototype models were made from transparent acrylic material.
Conclusion
Experimental Setup
A mixture of water and sodium polytungstate was used as a working fluid to match the refractive index of the flow and acrylic material constituting the airway model.
The results show the different pattern of the flow between these models. The nature complex of realistic respiratory tract has great effects to flow patterns. This PIV data was used to validate with numerical results. A quantitative comparison between experimental and simulated velocity profiles will be performed in the trachea region.
Contact:
Dr. Kazuhide Ito
Energy and Environmental Engineering Department
IGSES, Kyushu University
Phone:
Web page:
Results
The flow is characterized by the trachea section. In figure 4(1), the velocity vector distributions were almost uniform, and a relatively simple flow pattern was observed in idealized model. The vector map is almost identical and shows effect of straight tube to developed flow in the center of the trachea.
Acknowledgements
This project was supported by a Grant-in-Aid for Scientific Research (JSPS ).
Fig 2. Photograph depicting the accurate refracting index matching.