Numerical simulation of soft palate movement and airflow in human upper airway by fluid-structure interaction method

In this paper, the authors present airflow field characteristics of human upper airway and soft palate movement attitude during breathing. On the basis of the data taken from the spiral computerized tomography images of a healthy person and a patient with Obstructive Sleep Apnea-Hypopnea Syndrome (OSAHS), three-dimensional models of upper airway cavity and soft palate are reconstructed by the method of surface rendering. Numerical simulation is performed for airflow in the upper airway and displacement of soft palate by fluid-structure interaction analysis. The reconstructed three-dimensional models precisely preserve the original configuration of upper airways and soft palate. The results of the pressure and velocity distributions in the airflow field are quantitatively determined, and the displacement of soft palate is presented. Pressure gradients of airway are lower for the healthy person and the airflow distribution is quite uniform in the case of free breathing. However, the OSAHS patient remarkably escalates both the pressure and velocity in the upper airway, and causes higher displacement of the soft palate. The present study is useful in revealing pathogenesis and quantitative mutual relationship between configuration and function of the upper airway as well as in diagnosing diseases related to anatomical structure and function of the upper airway. The project supported by the National Natural Science Foundation of China (10672036, 10472025 and 10421002), the Natural Science Foundation of Liaoning Province (20032109). English text was polished by Yunming Chen.     

Numerical analysis of respiratory flow patterns within human upper airway

A computational fluid dynamics （CFD） approach is used to study the respiratory airflow dynamics within a human upper airway. The airway model which consists of the airway from nasal cavity, pharynx, larynx and trachea to triple bifurcation is built based on the CT images of a healthy volunteer and the Weibel model. The flow character- istics of the whole upper airway are quantitatively described at any time level of respiratory cycle. Simulation results of respiratory flow show good agreement with the clinical mea- sures, experimental and computational results in the litera- ture. The air mainly passes through the floor of the nasal cavity in the common, middle and inferior nasal meatus. The higher airway resistance and wall shear stresses are distrib- uted on the posterior nasal valve. Although the airways of pharynx, larynx and bronchi experience low shear stresses, it is notable that relatively high shear stresses are distrib- uted on the wall of epiglottis and bronchial bifurcations. Besides, two-dimensional fluid-structure interaction models of normal and abnormal airways are built to discuss the flow-induced deformation in various anatomy models. The result shows that the wall deformation in normal airway is relatively small.     

Numerical simulation of micro-particle deposition in a realistic human upper respiratory tract model during transient breathing cycle

An more reliable human upper respiratory tract model that consisted of an oropharynx and four generations of asymmetric tracheo-bronchial (TB) airways has been constructed to investigate the micro-particle deposition pattern and mass distribution in five lobes under steady inspiratory condition in former work by Huang and Zhang (2011). In the present work, transient airflow patterns and particle deposition during both inspiratory and expiratory processes were numerically simulated in the realistic human upper respiratory tract model with 14 cartilaginous rings (CRs) in the tracheal tube. The present model was validated under steady inspiratory flow rates by comparing current results with the theoretical models and published experimental data. The transient deposition fraction was found to strongly depend on breathing flow rate and particle diameter but slightly on turbulence intensity. Particles were mainly distributed in the high axial speed zones and traveled basically following the secondary flow. “Hot spots” of deposition were found in the lower portion of mouth cavity and posterior wall of pharynx/larynx during inspiration, but transferred to upper portion of mouth and interior wall of pharynx/larynx during expiration. The deposition fraction in the trachea during expiration was found to be much higher than that during inspiration because of the stronger secondary flow.     

鼻腔手术对OSAHS患者治疗效果的数值分析

对3名伴有鼻阻塞的OSAHS患者术前术后的上气道结构包含软腭组织进行三维重构,采用数值模拟的方法研究这3名患者手术前后,上气道气流分布以及软腭的运动情况,分析鼻腔手术对OSAHS患者的治疗效果.3名患者手术后鼻腔通气程度均得已改善.两名轻度OSAHS患者手术后上气道阻力减小,软腭位移均比术前减小,这些变化均有助于缓减呼吸时气流受限情况.而第3名重度患者手术后上气道阻力和软腭位移反而增加,这将会进一步加重气道的阻塞程度.鼻部手术对OSAHS患者的治疗效果取决于上游鼻腔通气程度的改善能否对下游咽腔产生有益的影响.数值模拟结果与PSG监测结果及其主诉情况相符,与现阶段临床有关的研究结论相一致,能够间接反映术后气道通气程度以及打鼾症状是否改善,为进一步解决临床的疑难问题提供了理论依据.     

鼻腔加温功能特征及其与气流场关系的研究

为研究鼻腔加温功能特征及其与气流场之间的关系, 选用1例健康国人的鼻腔进行CT扫描. 据CT数据对鼻腔气道进行表面三维重建, 运用计算流体动力学方法分析通气量为12L/min时吸气相0.15s, 0.45s, 0.75s的鼻腔气流场与温度场. 结果显示吸气相0.15s, 0.45s, 0.75s鼻腔气流场主要表现为双侧气流量分布不对称, 其中气流主要流经左侧; 双侧均为总鼻道中、下部气流量较多, 嗅裂、中鼻道和下鼻道气流量少. 吸气相0.15s, 0.45s, 0.75s温度场均表现为温度自鼻腔前端至鼻咽部逐渐增高, 其中温度主要上升区域为鼻内孔-下鼻甲前端-中鼻甲前端对应气道, 且在吸气速度和流量增大后, 这一主要加温区域无明显向后延长征象; 双侧鼻腔及单侧鼻腔不同部位气道气流分布差别较大, 但双侧温度场基本对称, 单侧鼻腔不同气道部位温度差值亦较小, 幅度均小于1℃.     

Numerical analysis for the efficacy of nasal surgery in obstructive sleep apnea hypopnea syndrome

In the present study, we reconstructed upper airway and soft palate models of 3 obstructive sleep apnea-hypopnea syndrome（OSAHS） patients with nasal obstruction. The airflow distribution and movement of the soft palate before and after surgery were described by a numerical simulation method. The curative effect of nasal surgery was evaluated for the three patients with OSAHS. The degree of nasal obstruction in the 3 patients was improved after surgery. For 2 patients with mild OSAHS, the upper airway resistance and soft palate displacement were reduced after surgery. These changes contributed to the mitigation of respiratory airflow limitation. For the patient with severe OSAHS, the upper airway resistance and soft palate displacement increased after surgery, which aggravated the airway obstruction. The effcacy of nasal surgery for patients with OSAHS is determined by the degree of improvement in nasal obstruction and whether the effects on the pharynx are beneficial. Numerical simulation results are consistent with the polysomnogram（PSG） test results, chief complaints, and clinical findings, and can indirectly reflect the degree of nasal patency and improvement of snoring symptoms, and further,provide a theoretical basis to solve relevant clinical problems.     

Toward numerical simulations of fluid–structure interactions for investigation of obstructive sleep apnea

Obstructive sleep apnea (OSA) is a medical condition characterized by repetitive partial or complete occlusion of the airway during sleep. The soft tissues in the airway of OSA patients are prone to collapse under the low-pressure loads incurred during breathing. This paper describes efforts toward the development of a numerical tool for simulation of air–tissue interactions in the upper airway of patients with sleep apnea. A procedure by which patient-specific airway geometries are segmented and processed from dental cone-beam CT scans into signed distance fields is presented. A sharp-interface embedded boundary method based on the signed distance field is used on Cartesian grids for resolving the airflow in the airway geometries. For simulation of structure mechanics with large expected displacements, a cut-cell finite element method with nonlinear Green strains is used. The fluid and structure solvers are strongly coupled with a partitioned iterative algorithm. Preliminary results are shown for flow simulation inside the three-dimensional rigid upper airway of patients with obstructive sleep apnea. Two validation cases for the fluid–structure coupling problem are also presented.     

An Attempt to Realize Experimental Isotropic Turbulence at Low Reynolds Number

This paper presents an attempt to realize experimental isotropicturbulence at low Reynolds number. For this aim an experimentalapparatus, a turbulence chamber “Box”, was designed and built togenerate a turbulent flow field in the center of the chamber. Theturbulent airflow field was generated by eight electrical fans placedsymmetrically at the eight internal corners of the externally cubicchamber. The turbulence intensity was controlled by the fans speed.Laser Doppler velocimeter (LDV) in single and two-point velocitymeasurements was used to fully characterize the turbulent field insidethe chamber. The main results indicate that the turbulence ishomogeneous and isotropic with a quasi-zero mean velocity within aspherical region of 20 mm radius from the center of the chamber. Themeasured turbulent integral length scale was found to be constant andindependent of the turbulence intensity (or fans speed). Furthermore, anoticeable spectral inertial subrange as prescribed by the Kolmogorovtheory has not been observed at the range of Reynolds number exploredhere, where Re_λ < 100. But rather a scaling region characterized by anexponent that is lower than the Kolmogorov value, ?5/3, has beenidentified. Moreover, the value of this exponent showed no definedtrend, while the width of the inertial scaling region expands as themicroscale Reynolds number increases.     

平面激波冲击并排液滴的三维数值模拟研究

采用三维守恒清晰界面数值方法, 研究平面激波冲击并排液滴的动力学过程. 研究的焦点在于激波接触液滴后的复杂波系结构生成, 以及并排液滴相互耦合作用诱导的单个液滴非对称界面演化. 首先, 分析并排液滴之间界面通道内的波系结构发展, 发现在冲击初期由于反射激波相交而形成新的反射激波以及马赫杆; 这些流动现象与液滴另外一侧 (非通道侧) 由激波反射所形成的弯曲波阵面截然不同, 而且所导致的液滴横向两侧流场差异是中后期冲击过程液滴两侧界面非对称演化的主要原因. 其次, 研究冲击中期时, 特别是入射激波已运动至液滴下游并远离并排液滴, 界面形态的演化过程和规律, 揭示通道下游出口处由于气流膨胀导致的界面闭合、以及随后气流阻塞导致的界面破碎等新的流动现象. 最后, 研究液滴间距对并排液滴相互作用的影响规律, 发现液滴间距大小与通道内压力峰值具有明显的关联关系. 研究表明, 更小的液滴间距不仅带来更大的压力峰值, 而且使得峰值出现的时间更早.      

Influence of staff number and internal constellation on surgical site infection in an operating room

Prediction of bacteria-carrying particle （BCP） dispersion and particle distribution released from staffmem- bers in an operating room （OR） is very important for creating and sustaining a safe indoor environment. Postoperative wound infections cause significant morbidity and mortality, and contribute to increased hospitalization time. Increasing the number of personnel within the OR disrupts the ventilation airflow pattern and causes enhanced contamination risk in the area of an open wound. Whether the amount of staffwithin the OR influences the BCP distribution in the surgical zone has rarely been investigated. This study was conducted to explore the influence of the number of personnel in the OR on the airflow field and the BCP distribution. This was performed by applying a numerical calculation to map the airflow field and Lagrangian particle tracking （LPT） for the BCP phase. The results are reported both for active sampling and passive monitoring approaches. Not surprisingly, a growing trend in the BCP concentration （cfu/ms） was observed as the amount of staff in the OR increased. Passive sampling shows unpredictable results due to the sedimentation rate, especially for small particles （5-10 i~m）. Risk factors for surgical site infections （SSls） must be well understood to develop more effective prevention programs.     

Low Reynolds-number moment on asymmetric bodies

The moment induced on asymmetric particles by a low Reynolds-number flow is examined. A flat disk and a half sphere are suspended in low-velocity airflow and the moment exerted on the particles is measured as a function of Reynolds number and approach angle. Object Reynolds-numbers range between 20 and 200, and the measured moment is in the nNm range. A moment coefficient (a moment normalized with the drag force and object radius) is calculated from the moment measurements and found to generally decrease with increasing Reynolds number. Stable approach angle positions are identified for the objects in the flow, and it is shown that the objects tend to rotate towards the position of maximum drag (local extremum) from other approach angles. The present measurements are consistent with previous qualitative observations of free-falling particles.     

同轴气流式液体射流分裂液滴粒径研究

针对同轴气流式液体射流分裂液滴粒径预测模型缺乏的现状,结合射流线性稳定性理论,建立了基于临界模数的同轴气流式黏性液体射流分裂液滴粒径表达式,在此基础上,分别研究了气流旋拧(气流同时存在轴向和周向运动)及流体物性(气体可压缩性、液体黏性、气液密度比和表面张力)对液滴粒径的影响规律.研究发现:周围气流轴向引射作用和同轴旋转...     

Experimental investigation of heat transfer in a packed duct with unequal wall temperatures

Wall-to-air forced convective heat transfer has been measured in a rectangular duct with unequal wall temperatures. The measurements were taken for a developing region in laminar flow. A uniform heat flux was supplied to the front wall of the duct. Heat transfer coefficients were measured in the empty and packed duct for various airflow rates and for different diameters of Raschig ring type packings. Measurements indicate that there is a considerable increase in the value of heat transfer coefficient for a packed duct over that for a duct with an empty flow passage.     

Stereoscopic PIV measurements of flow in the nasal cavity with high flow therapy

Knowledge of the airflow characteristics within the nasal cavity with nasal high flow (NHF) therapy and during unassisted breathing is essential to understand the treatment’s efficacy. The distribution and velocity of the airflow in the nasal cavity with and without NHF cannula flow has been investigated using stereoscopic particle image velocimetry at steady peak expiration and inspiration. In vivo breathing flows were measured and dimensionally scaled to reproduce physiological conditions in vitro. A scaled model of the complete nasal cavity was constructed in transparent silicone and airflow simulated with an aqueous glycerine solution. NHF modifies nasal cavity flow patterns significantly, altering the proportion of inspiration and expiration through each passageway and producing jets with in vivo velocities up to 17.0 ms⁻¹ for 30 l/min cannula flow. Velocity magnitudes differed appreciably between the left and right sides of the nasal cavity. The importance of using a three-component measurement technique when investigating nasal flows has been highlighted.     

Parametric study on the fuel film breakup of a cold start PFI engine

In order to provide more insight on improving the cold start fuel atomization for reducing unburned hydrocarbon emissions, the liquid fuel film breakup phenomenon in the intake valve/port region was investigated in depth for port-fuel-injected engines. Experiments were conducted using high-speed high-resolution imaging techniques to visualize the liquid film atomization and airflow patterns in an axisymmetric steady flow apparatus. The impact of valve/port seat geometry, surface roughness, and fuel properties on airflow separation and fuel film breakup were determined through a parametric study. CFD simulations were also performed with FLUENT to help understand the airflow behavior inside the intake port and valve gap region and its potential impact on fuel film atomization.     

An experimental study on turbulent coherent structures near a sheared air-water interface

The turbulence structures near a sheared air-water interface were experimentally investigated with the hydrogen bubble visualization technique. Surface shear was imposed by an airflow over the water flow which was kept free from surface waves. Results show that the wind shear has the main influence on coherent structures under air-water interfaces. Low- and high- speed streaks form in the region close to the interface as a result of the imposed shear stress. When a certain airflow velocity is reached, “turbulent spots” appear randomly at low-speed streaks with some characteristics of hairpin vortices. At even higher shear rates, the flow near the interface is dominated primarily by intermittent bursting events. The coherent structures observed near sheared air-water interfaces show qualitative similarities with those occurring in near-wall turbulence. However, a few distinctive phenomena were also observed, including the fluctuating thickness of the instantaneous boundary layer and vertical vortices in bursting processes, which appear to be associated with the characteristics of air-water interfaces. The project supported by the National Natural Science Foundation of China (Grant No.19672070)     

等离子体EHD顺电加速效应影响因素实验研究

利用PIV系统,在静止空气中,定量测量了等离子体激励器的诱导速度场,分析了激励参数等因素对等离子体EHD顺电加速效应的影响。通过实验发现:在激励频率固定的情况下,诱导气流速度随着电压的升高逐渐增大;在激励电压固定的情况下,存在一个诱导气流速度最大的最优频率,并且不同的激励器对应不同的最优频率。另外,初步分析了激励器布局、绝缘材料以及通电时间对诱导气流速度的影响。     

Optimal control of the transmission dynamics of tuberculosis

This paper deals with the problem of optimal control for the transmission dynamics of tuberculosis (TB). A tuberculosis model which incorporates the essential biological and epidemiological features of the disease such as exogenous reinfection and chemoprophylaxis of latently infected individuals, and treatment of the infectious is developed and rigorously analyzed. Based on this continuous model, the tuberculosis control is formulated and solved as an optimal control theory problem, indicating how a control term on the chemoprophylaxis should be introduced in the population to reduce the number of individuals with active TB. The feedback control law has been proved to be capable of reducing the number of individuals with active TB. An advantage is that the proposed scheme accounts for the energy wasted by the controller and the closed-loop performance on tracking. Numerical results show the performance of the optimization strategy.