| Human upper respiratory tract is an important part of respiratory system andthe main exchange channel for gas between the body and the outside environment.With the increase in threat of international bioterrorism, the development of sanitaryprotection and epidemic prevention technology and the deterioration of atmosphericenvironment, the importance of the research on airflowment and particle diffusionin human upper respiratory tract have gradually aroused more attention. Whenbioterrorism attacks happen, a large number of virus aerosols entered and do harmto human body via upper respiratory tract. Although most of virus aerosols can befiltered effectively by sanitary cabin with the function of biological protection, thelittle can also entered the cabin and accumulated in human body, which also candamage human health. The incidence of respiratory diseases caused by atmospherepollution increased year by year, and the complexity and severity of the diseases isincreasingly outstanding, which has seriously influenced the quality of life.The standardized model of human upper respiratory tract was constructed, andthe methods of integrating numerical simulation with PIV experimental researchwere used to study the airflowment, vortex evolution and aerosol deposition in thestandardized model under the effect of fluid-solid interaction both in steady andcyclic respiratory pattern. The main conclusions of the present work aresummarized as followed:The3D standardized model of human upper respiratory tract wasconstructed. The technology of3D reconstruction and sophisticated imageprocessing was used to construct3D standardized model of human upperrespiratory tract by the processes of CT scanning for upper respiratory tracts,3Dreconstruction of individual upper respiratory tract, normalization of individualmodels, slicing individual models, fusion of slicing image and standardization ofthe model, and then the difference between standardized model and the previousmodel was analyzed qualitatively and quantitatively. The results show that:compared to the simplified model, the standardized model is more similar to the realhuman upper respiratory tract in the completeness of structural characteristics andthe reality of geometry, and it possesses more application value in scientificresearch.The fluid-solid interaction was analyzed in human upper respiratory tract. The fluid solid interaction mechanics model is built and used to simulate airflowmovement in human upper respiratory tract model, and the shape change of themodel wall and the airflow in the model were analyzed. The results show that:Under the effect of fluid-solid interaction, the larger the respiratory flow is, thegreater the shape of respiratory tract changes, and the stronger the buffer effectworks on the airflow. In the phase of inhalation, the throat and trachea movebackward, the anterior wall was stretched, and the posterior wall was compressed,meanwhile airflow movement causes the expansion of throat. In the phase ofexhalation, the throat and trachea moves forward, the anterior wall was compressed,and the posterior wall was stretched, meanwhile airflow movement causes theshrinkage of throat.In the phase of cyclic inhalation, high velocity zone is created in pharynx andlarynx, and the phenomenon of airflow separation appeared in the pharynx. Aturbulence jet appears in the glottal region because of the restriction of geometricstructure, and the airflow separates in the downstream of the glottis with theseparation zone appearing near the posterior wall of the upper part of the trachea,and with high velocity zone appearing near the anterior wall. With the increase inthe distance with glottis, the velocity difference between the anterior and posteriorwall of the trachea gradually decreases. In the phase of cyclic exhalation, thevelocity of airflow near the hard palate and soft palate is higher than that on thebottom of mouth, and the phenomenon of airflow separation appears on the top. Theairflow streams converge at the bifurcation of trachea and bronchi, which causes thevelocity in the center of the bifurcation is lower. Meanwhile the confluence alsocauses two temporary airflow streams with higher velocity appear in the superiorbronchus, and then converges gradually.The vortex evolution in human upper respiratory tract under the effect offluid-solid interaction was simulated. Large eddy simulation and fluid-solidinteraction mechanics was used to simulate the process of vortex evolution and theresults show that:In the phase of inhalation, several vortex tubes were formed in the central ofmouth because the air near the hard palate rubs against the inlet airflow streams andwith the barrier of tongue coating some vortex tubes also appear on the surface oftongue coating. Then, transition occurred in the pharynx with disturbance of softpalate and the turning of airway. A turbulence jet ejected towards to the anteriorwall of the trachea appeared in the glottal regional. Affected by the barrier of thetrachea wall, the "horseshoe vortexes" which are similar to horseshoe appeared onthe anterior wall of the trachea.In the phase of exhalation, the airflow streams converged at the bifurcation of trachea and bronchi, and the confluence caused the complex vortex structure on thebottom of the trachea. With the airflow streams converging, the vorticity in thetrachea decreased, and only a stronger vortex tube was extended along with thetrachea. The intense jet in the glottal regional and the barrier of epiglottis causedcomplex vortex structures in throat, and "arch vortex" are formed on the posteriorwall of throat. When the airflow entered the mouth, the vortex structures broke upand a jet was ejected towards to the top of mouth because of the barrier of softpalate, turning of the airway and the shrinkage of cross-section in pharynx, in themeanwhile, there were no big vortex structure in the mouth.The diffusion and deposition of aerosol particles in human upper respiratorytract under the effect of fluid-solid interaction was studied. The lagrangianstochastic trajectory model and fluid-solid interaction mechanics were used tosimulate the deposition and diffusion of the aerosol particles, and the results showthat:In the phase of inhalation, the aerosol particles with size of0.3mwere morelikely to pass through upper respiratory tract and get to the lower bronchus than theparticles with size of6.5m. Easily affected by the vortex structures, more aerosolparticles with size of0.3mwith the helicoidally trajectories appeared on theposterior wall of larynx and trachea, and most of particles passed through theregions with higher airflow vorticity. In the phase of exhalation, the aerosolparticles entrained by the exhalation flow returned, convoluted and deposited in thetract. And some of the aerosol particles were taken out of mouth during this process.The trajectories of the reentrant particles were congregated in regions with higherairflow vorticity due to the good following performance of the particles.Both under the conditions that the respiratory flow are30L/min and60L/min,the deposition fraction of the aerosol particles with sizes of0.3mand6.5minthroat and trachea was high, and that in the mouth was low. And the depositionfraction of the aerosol particles with size of6.5min different zones of the upperrespiratory tract is obviously higher than that with size of0.3m. With the effect offluid-solid interaction, the deposition fractions of the sizes of0.3mand6.5min the throat will decrease. The main mechanism of deposition for the particles withsize of6.5mis inertial impaction, and the deposition for the particles with size of0.3mis more likely to be effected by turbulent dispersion and entrainment ofeddy current.The visualization experiment researches on airflow movement, vortexevolution and aerosol deposition were performed. The Stereolithography (SL)technology was used to construct the replica of human upper respiratory tract for experiment, and the Particle Image Velocity (PIV) technology was applied tomearsure the airflow movement, vortex evolution and aerosol deposition. The resultfrom the experiment was contrasted with that from simulation, which vertified theaccuracy of the simulation method. The results show that: the result of experimentis consistent with that of simulation in the air distribution mode. The maximumvelocity in the simulation is10.24m/s, and that in the experiment is9.55m/s. Themaximum error of the velocity between the two results is not over8%, and the trendof the aerosol deposition in the parts of human upper respiratory tract wasconsistent, which both verified that the numerical simulation methods are accurateand reasonable. |
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