Numerical Simulation On The Flow Field And Deposition Of Inhaled Particles In Human Pulmonary Acinus Region

Biosafety level 4 laboratory is a place for experimental operations of high-risk pathogenic microorganisms,where has a certain biosafety risk.Pathogenic microorganisms can enter human body through the respiratory tract in the form of aerosol particles,then spread,deposit,replicate and cause disease in the respiratory tract mucosa and lung,which poses a serious threat to human health and life safety.On the other hand,the atmospheric environment continues to deteriorate,and fine particulate matter such as PM2.5 can enter the respiratory tract with breathing,leading to the decline of lung function and the increase of infection and respiratory symptoms.Studying the flow field and deposition of inhaled particles in human acinar region also helps to increase the deposition rate of drug particles in the lesion area and enhance the targeting of drug effects.Due to complex and relative samller size of alveolar structure,it is not yet possible to obtain a realistic computer or entity model.The models in current research have been greatly simplified,the authenticity and integrity of which need to be improved.Furthermore,most of the current research focus on the final deposition fraction of inhaled particles in human acinar region,but little is involved with its dynamic deposition characteristics,making it difficult to further understand the movement and dynamic deposition characteristics of inhaled particles in human acinar region.In addition,during the human breathing period,the actual movement of the lung acinar should be passive deformation under the pressure of the lungs.However,in the current research,the wall motions of lung acinar model are mostly rigid or isotropic,which cannot reflect the real respiratory physiological characteristics of pulmonary acinar,different greatly from the actual movement of pulmonary acinar.Therefore,it is important to establish a more realistic and complete lung acinar model and systematically study the flow field and deposition of inhaled particles in human acinar region.Based on previous research,human pulmonary acinar models were built which are more in line with the actual human body in this thesis.Numerical simulation was performed systematically to study the effects of some factors on the flow field and deposition status of inhaled particles in human acinar region,such as different particle diameter,pulmonary acinar models,breathing patterns,direction of gravity,and wall motion of the model.The main work and research results are as follows:(1)Based on the Weibel A model,five human pulmonary acinar models,from G3 to G7,were established,and each model was meshed.The control equations were established,and numerical simulation methods were selected,and boundary conditions were set.The establishment of human pulmonary acinar model provids models for subsequent numerical simulation research.(2)The numerical simulation on the flow field and deposition characteristics of particles with different diameter in G3 ～ G7 models was studied.The evaluation parameter 1/4 deposition time was introduced to study the particle deposition speed,and the characteristics of the particle deposition curves with variable diameter were analyzed.The results show that with the increase of the generation,the flow field in the alveoli changes from circular to radial.The volume,length and geometry of model have a significant effcet on the deposition of particles.From G3 to G7 model,the deposition speed increases.The deposition curve of 0.1 μm particle is logarithmic.In addition,the deposition curve of 5 μm particle showed an “S” shape distribution.The deposition curves of 0.3 μm and 3 μm particles is lower logarithmic and lower “S” curve,respectively.The deposition curves of other particle sizes are broken lines.(3)The G5 model was used to analyze the effects of tidal volume and respiratory cycle on the flow field and final deposition rate and speed of inhaled particles with different diameter numerically.The effects of directions of gravity on the deposition of particles were studied.The results show that the streamline is only affected by the structure of the model,and the breathing patterns have no effect on the streamline in human acinar region.The tidal volume has a postive effect on the increase of particle deposition rate and speed,and the breathing cycle has a postive effect on the increase of particle deposition rate but a negative one on speed.Under the same breathing pattern,as the particle diameter increases,the deposition rate shows a U-shaped curve,while 1/4 deposition time shows an inverted U curve.The direction of gravity has little effect on the particle deposition rate,but affects the particle deposition location.(4)The dynamic grid algorithm was used to study the effect of the model’s sinusoidal expansion and contraction motion on the flow field and particle deposition.The results show that the designed dynamic grid algorithm can realize the expansion and contraction movement of the model in the sinusoidal mode,and the maximum error of the model entrance speed compaired with the rigid mode is 5.23%.Under the model’s sinusoidal expansion and contraction motion,the circulation flow is absent.The tidal volume has a slight incrase on the deposition of partcles,while does not affect the streamline in human acinar region.The change of particle deposition rate in the G5 model with diameter increasing is consistent with the trend in the rigid mode generally.The difference lies in the lowest point of the U-shaped curve.Besides,the U-shaped curve is steeper in the rigid mode,which is gentler in the sinusoidal one.What is more,the convection caused by wall motion can make small particles being in longer suspension period,which means a single cycle is not enough to investigate the deposition law of the particles.Therefore,numerical simulation research under multi-breathing cycle can be more realistic.(5)A fluid-solid coupling mechanical model of the alveolar sac was established,and the structural changes of the alveolar sac driven by airflow and pressure were studied.The effects of fluid-solid coupling motion on the flow field and deposition rate of particles were compared and studied.The results show that the deformation of the alveolar sac structure is dominant by pressure,and airflow has a negligible effect.Under three types of wall motion,the wall movement of the model under the fluid-solid coupling motion can significantly change the internal streamlines.In terms of deposition rate,the particle deposition rate in the sinusoidal mode increases slightly compared to the rigid mode,about 5%,while the particle deposition rate is greatly improved under the fluid-solid coupling motion,which indicates that the fluid-solid coupling motion is an important factor affecting the particle deposition rate.In summary,the flow flied and the deposition status of inhaled particles in human acinar region were numerically studied under the influence of multiple factors in this paper.Human alveolar models with various size data consistent with the literature were established,which can meet the needs of different numerical simulations for models.The introduction of the parameter 1/4 of the deposition time provides a new perspective to evaluate the deposition speed of particulate matter.The dynamic process of inhaled particles deposition was studied,and the characteristics of the particle deposition curve of each diameter were summarized.The leading role of pressure in driving the structural changes of the alveolar sac was confirmed.The effects of fluid-solid coupling motion on the deposition rate were compared and studied,having a lot of value to the further exploration of the dynamic deposition characteristics and fluid-solid coupling motion of inhaled particles in human acinar region.