Large eddy simulation and zonal modeling of human-induced contaminant transport

An immersed boundary method for particulate flow in an Eulerian framework is utilized to examine the effects of complex human motion on the transport of trace contaminants. The moving human object is rendered as a level set in the computational domain, and realistic human walking motion is implemented using a human kinematics model. A large eddy simulation (LES) technique is used to simulate the fluid and particle dynamics induced by human activity. Parametric studies are conducted within a Room-Room and a Room-Hall configuration, each separated by an open doorway. The effects of the average walking speed, initial proximity from the doorway, and the initial mass loading on room-to-room contaminant transport are examined. The rate of mass transport increases as the walking speed increases, but the total amount of material transported is more influenced by the initial proximity of the human from the doorway. The Room-Hall simulations show that the human wake transports material over a distance of about 8 m. Time-dependent data extracted from the simulations is used to develop a room-averaged zonal model for contaminant transport due to human walking motion. The model shows good agreement with the LES results. PRACTICAL IMPLICATIONS: The effect of human activity on contaminant transport may be important in applications such as clean or isolation room design for biochemical production lines, in airborne infection control, and in entry/exit into collective protection or decontamination systems. The large eddy simulations (LES) performed in this work allow precise capturing of the local wakes generated by time-dependent human motion and thus provide a means of quantifying contaminant transport due to wake effects. The LES database can be used to develop zonal models for the bulk effects of human-induced contaminant transport. These may be incorporated into multi-zone infiltration models for use in threat-response and exposure mitigation studies.     

Dynamic airflow simulation within an isolation room

In many hospitals, isolation rooms are used to contain patients who are highly infectious, and the spread of air and bacteria within the isolation room is closely relates to room air distribution. This article uses the computational fluid dynamics (CFD) method to investigate the effects of a moving person and the opening and closing of a sliding door on room air distribution, including velocity, pressure and contaminant fields. Dynamic meshes are employed to simulate the movement of the walking person and sliding door. According to numerical results, the impact of those moving objects on room air distribution is addressed in this study.     

A simulation study of ventilation and indoor gaseous pollutant transport under different window/door opening behaviors

The window/door opening behavior of occupants is a very important factor in determining the airflows and ventilation conditions in buildings, on which indoor pollutant concentration and transport are highly dependent. A two-room residence model was simulated in this study to analyze the airflow characteristics and pollutant transport under different window/door opening behaviors. Airflows were unidirectional and the residence could not be treated as a well-mixed zone when there were no temperature differences. If there were temperature differences, two-way airflow occurred at the exterior window of the room when it was open and the interior door was closed, resulting in a much larger ventilation rate than the situation without temperature differences. Strong two-way airflow occurred at the interior door in the case of the exterior window closed and interior door open, as the air in the two connected rooms was well mixed after the interior door was opened for tens of minutes. The ventilation rate of the room with double-sided ventilation was much higher than that of the room with single-sided ventilation, even though the total opening areas were the same. Opening the exterior window and closing the interior door could effectively remove pollutants from a polluted room and prevent their transport to a clean room. Field experiments were performed and the main conclusions of the simulation were verified.     

Large-eddy simulation of the containment failure in isolation rooms with a sliding door—An experimental and modelling study

In hospital isolation rooms, door operation can lead to containment failures and airborne pathogen dispersal into the surrounding spaces. Sliding doors can reduce the containment failure arising from the door motion induced airflows, as compared to the hinged doors that are typically used in healthcare facilities. Such airflow leakage can be measured quantitatively using tracer gas techniques, but detailed observation of the turbulent flow features is very difficult. However, a comprehensive understanding of these flows is important when designing doors to further reduce such containment failures. Experiments and Computational Fluid Dynamics (CFD) modelling, by using Large-Eddy Simulation (LES) flow solver, were used to study airflow patterns in a full-scale mock-up, consisting of a sliding door separating two identical rooms (i.e. one isolation room attached to an antechamber). A single sliding door open/ hold-open/ closing cycle was studied. Additional variables included human passage through the doorway and imposing a temperature difference between the two rooms. The general structures of computationally-simulated flow features were validated by comparing the results to smoke visualizations of identical full-scale experimental set-ups. It was found that without passage the air volume leakage across the doorway was first dominated by vortex shedding in the wake of the door, but during a prolonged hold-open period a possible temperature difference soon became the predominant driving force. Passage generates a short and powerful pulse of leakage flow rate even if the walker stops to wait for the door to open.     

Transport of airborne particles within a room

The objective of this study is to test a technique used to analyze contaminant transport in the wake of a bluff body under controlled experimental conditions for application to aerosol transport in a complex furnished room. Specifically, the hypothesis tested by our work is that the dispersion of contaminants in a room is related to the turbulence kinetic energy and length scale. This turbulence is, in turn, determined by the size and shape of furnishings within the room and by the ventilation characteristics. This approach was tested for indoor dispersion through computational fluid dynamics simulations and laboratory experiments. In each, 3 mum aerosols were released in a furnished room with varied contaminant release locations (at the inlet vent or under a desk). The realizable k approximately epsilon model was employed in the simulations, followed by a Lagrangian particle trajectory simulation used as input for an in-house FORTRAN code to compute aerosol concentration. For the experiments, concentrations were measured simultaneously at seven locations by laser photometry, and air velocity was measured using laser Doppler velocimetry. The results suggest that turbulent diffusion is a significant factor in contaminant residence time in a furnished room. This procedure was then expanded to develop a simplified correlation between contaminant residence time and the number of enclosing surfaces around a point containing the contaminant. Practical Implications The work presented here provides a methodology for relating local aerosol residence time to properties of room ventilation and furniture arrangement. This technique may be used to assess probable locations of high concentration by knowing only the particle release location, furniture configuration, inlet and outlet locations, and air speeds, which are all observable features. Applications of this method include development of 'rules of thumb' for first responders entering a room where an agent has been released and selection of sampler locations to monitor conditions in sensitive areas.     

Numerical investigation of influence of human walking on dispersion and deposition of expiratory droplets in airborne infection isolation room

This paper introduces a numerical simulation model for investigating the influence of moving subjects on the dispersion and deposition of expiratory droplets, rather than on the dispersion of surrogate gaseous counterparts generally adopted in related research works. In our work, the Lagrangian discrete trajectory model is used for tracing the motion of droplets, the Eulerian RANS method is used for solving the airflow field, and the dynamic mesh model for describing the human movement. The model validation was performed through result comparisons with published data from literatures. A case study on the influence of human walking on the dispersion and deposition of expiratory droplets in an airborne infection isolation room (AIIR) is then presented. Our findings show that the human walking disturbs the local velocity field with wake formation. The increase of walking speed could effectively reduce the overall number of suspended droplets, which may have a positive impact on releasing the infection risk of health workers in AIIR.     

Analytical solutions for contaminant diffusion in four-layer sediment-cap system for subaqueous in-situ capping

This paper presents analytical solutions for predicting one-dimensional contaminant diffusion in a four-layer sediment-cap system, which is typically encountered in subaqueous in-situ capping of contaminated sediments. The sediment-cap system is comprised of, from top to bottom, a layer of capping material (e.g., clean sand), a layer of reactive core mat (RCM), a layer of contaminated sediment and a layer of uncontaminated sediment. Two different bottom boundary conditions are considered, i.e., zero-concentration-gradient bottom boundary condition and zero-concentration bottom boundary condition, for which the method of separation of variables is used to obtain the analytical solutions. The extensively verified CST3 (Consolidation and Solute Transport 3) model is used to verify the proposed analytical solutions. Using the verified analytical solutions, parametric studies are conducted to investigate the effect of several important parameters on contaminant transport in the four-layer sediment-cap system. The results indicate that the cap thickness, the contaminated sediment thickness, the uncontaminated sediment thickness, the effect of RCM, and the RCM distribution coefficient have significant impact on contaminant diffusion in the four-layer sediment-cap system. The analytical solutions presented herein can be used to assist the design of subaqueous in-situ capping of contaminated sediments and to verify other numerical models.     

Influence of movements on contaminant transport in an operating room

The influence of persons' movements on contaminant transport during an orthopedic surgical operation is examined. Orthopedic surgical operations require an ultra clean environment usually provided by a LAF device (laminar airflow). During hip replacements bone cement is sometimes applied. Due to practical reasons cement mixing is performed outside the LAF area. During the cement transport from the mixing location to the surgeon there is a potential risk of bacterial transport to the clean zone. This phenomenon is examined by smoke visualization and computational fluid dynamics (CFD). The movements are modeled by CFD using distributed momentum sources as well as a turbulent kinetic energy source. A significant risk of contaminant transport from the less clean zone to the ultra clean zone is found. The results indicate that it is possible to simulate the influence of movements using a relatively simple CFD model that considers the significant influence of a transient phenomenon in an approximate way. PRACTICAL IMPLICATIONS: In real-life ventilated enclosures like operating rooms movements take place. Persons' movements may influence the local flow field as well as the contaminant field substantially. Most often movements are ignored in simulations due to the complexity of the phenomenon. This paper presents an indirect and simple method to consider the influence of movements that may enable modelers to include this important phenomenon in the engineering application of CFD. This may improve practical risk assessment--for instance risk assessment of unintended transport of bacteria during orthopedic surgical operations that may jeopardize the hygiene.     

Prompt tracking of indoor airborne contaminant source location with probability-based inverse multi-zone modeling

Indoor air quality (IAQ) has a significant influence on occupants' comfort, health, productivity, and safety. Existing studies show that the primary causes of many IAQ problems are various airborne contaminants that either are generated indoors or penetrate into indoor environments with passive or active airflows. Accurate and prompt identification of contaminant sources can help determinate appropriate IAQ control solutions, such as, eliminating contaminant sources, isolating and cleaning contaminated spaces. This study develops a fast and effective inverse modeling method for identifying indoor contaminant source characteristics. The paper describes the principles of the probability-based adjoint inverse modeling method and formulates a multi-zone model based inverse prediction algorithm that can rapidly track contaminant source location with known source release time in a building with many compartments. The paper details the inverse modeling procedure with modification of an existing multi-zone airflow and contaminant transport simulation program. The application of the method has been demonstrated with two case studies: contaminant releases in a multi-compartment residential house and in a complex institutional building. The numerical experiments tested the source identification capability of the program for various contaminant sensing scenarios. The investigation verifies the effectiveness and accuracy of the developed method for indoor contaminant source tracking, which will be further explored to identify more complicated indoor contamination episodes.     

Simulation of vertical concentration gradient of influenza viruses in dust resuspended by walking

Particles are resuspended from the floor by walking and are subject to turbulent transport in the human aerodynamic wake. These processes may generate a vertical concentration gradient of particles. To estimate the magnitude of turbulence generated by walking, we measured the velocity field in the wake from floor to ceiling at 10‐cm intervals with a sonic anemometer. The resulting eddy diffusion coefficients varied between 0.06 and 0.20 m²/s and were maximal at ~0.75–1 m above the floor, approximately the height of the swinging hand. We applied the eddy diffusion coefficients in an atmospheric transport model to predict concentrations of resuspended influenza virus as a function of the carrier particle size, height in the room, and relative humidity, which affects the resuspension rate coefficient and virus viability. Results indicated that the concentration of resuspended viruses at 1 m above the floor was up to 40% higher than at 2 m, depending on particle size. For exposure to total resuspended viruses, the difference at 1 vs. 2 m was 11–14%. It is possible that shorter people are exposed to higher concentrations of resuspended dust, including pathogens, although experimental evidence is needed to verify this proposition.     

Experimental and theoretical investigation of particle-laden airflow under a prosthetic mechanical foot in motion

This research effort was aimed at understanding how foot motion affects air transport and thus how walking affects contaminant dispersion. Particle imaging velocimetry (PIV) showed that during a rotational motion of the foot (typical footstep), a draft corner flow develops that carries particles from heel to toe. Foot contact with the floor may result in one or both of two types of reentrainment: (1) particles become airborne due to detachment from the floor, and (2) particles are first collected by the foot cover (e.g., Tyvek) and then detached from the foot into the airflow produced by the foot rotation. The airflow under the rotating foot was modeled as a rotating corner flow, and it was shown that such modeling can capture major characteristics of the airflow generated by the rotating foot and can explain how rotational foot motion contributes to reentrainment and dispersion of contaminants.     

福建永安青水长庆堂木构节点初探

本文在调研测绘的基础上对福建永安青水民居长庆堂的构造节点进行了探讨。通过对大门、倒座、厢房、正房这一系列中轴空间中的柱顶节点、檐口节点的分析．指出其构造节点具有符合穿斗结构，增加辅助构件、利用榫卯开口的特征。这对进一步理解其合院护拢形的空间形制具有重要意义。     

创造东滩生态区绿色交通系统

东滩的规划目标是建成崇明岛标志性的生态示范区、入口景区和休闲运动区。城市规划，城镇体系的发展与其目标的实现与交通是密不可分的，交通对引导城市实现其发展目标，支撑城镇体系的发展发挥了极其重要的作用。东滩要建设成为上海远郊生态新城区，需要发展适合生态型城镇的绿色交通。     

The effects of simulated fire pressure and outside wind on the internal pressure distribution in a five-storey model building

This paper presents some of the wind tunnel pressure measurements made on a five-storey model building (32 cells), with a vertical shaft and fixed leakage characteristics. Internal and external pressures measurements are presented for various wind angles and a simulated fire pressure in a room on floor 2 and floor 4. Comparison is made to assess the effect of fire on internal pressure distribution. Although the results are presented for all the wind angles investigated, a detailed discussion is confined only to a single wind angle. Implications of the combined effect of wind and fire on the shaft pressurization system design calculations must take these two factors into account.

In a fire situation it is possible that escapers may leave some of the shaft doors open or the fire room door may burn down. In such a case the pressurization system can become ineffective, causing escape routes to get smoke-logged. The effect of a combination of fire door openings was also investigated. The results for the following door opening combinations are presented and discussed:

1. (i) shaft door open alone;

2. (ii) fire room door open alone;

3. (iii) shaft and fire room doors open together.

It is shown quite clearly that these openings are significant for a range of wind angles.     

Influence of human movement on the transport of airborne infectious particles in hospital

The impacts of human movement on the distribution of airborne infectious particles in hospital environment are investigated numerically. In the case of airborne infection isolation room, the influence of different walking speeds on the distribution of respiratory droplets is investigated by adopting the Lagrangian method for tracing the motion of droplets, the dynamic mesh model for describing human walking and the Eulerian unsteady Reynolds-averaged Navier–Stokes model for solving the airflow. In the case of operating theatre, the impact of surgeon bending movement on the distribution of bacteria-carrying particles (BCPs) is investigated by using a similar approach, except that the drift-flux model is used for modelling BCPs distribution. The adopted models are successfully validated against reported experimental data. The results show that both walking speed and bending posture change considerably the suspended droplets concentration in a room. The key factors regarding the simulation techniques are discussed.     

The effect of source motion on contaminant distribution in the cleanrooms

In the recent decades, cleanrooms have found growing applications in broad range of industries such as pharmacy and microelectronics. Concerns about negative effects of the contaminant exposure on the human health and product quality motivate many researchers towards understanding of the airflow and contaminant distribution though these environments. With an improvement in computational capacity of the computers, computational fluid dynamics (CFD) technique has become a powerful tool to study the engineering problems including indoor air quality (IAQ). In this research, indoor airflow in a full-scale cleanroom is investigated numerically using Eulerian-Eulerian approach. To evaluate the ventilation system effectiveness, a new index, called final efficiency, is introduced which takes all aspects of the problem into account. The results show that the contaminant source motion and its path have a great influence on the contaminant dispersion through the room. Based on the results, the contaminant distribution indexes, e.g. final efficiency and spreading radius, are improved when the source motion path is in the dominant direction of the ventilation airflow. Consequently, the efficiency of an air distribution system which provides a directional airflow pattern shows the least source path dependency. This study and its results may be useful to gain better understanding of the source motion effects on the indoor air quality (IAQ) and to design more effective ventilation systems.     

无障碍前门的电子方案

结构细部,比如门的特殊宽度或没有门槛的通道,其在无障碍前门和入口区的设计中是极其重要的。然而,其重要性丝毫不逊色于结构细部的是门锁与门的易操作性,在此种情况下,至关重要的便捷水平就要通过供电构件来提供。     

Personal Exposure in Displacement Ventilated Rooms

Personal exposure in a displacement ventilated room is examined. The stratified flow and the considerable concentration gradients necessitate an improvement of the widely used fully mixing compartmental approach. The exposure of a seated and a standing person in proportion to the stratification height is examined by means of full-scale measurements. A breathing thermal manikin is used to simulate a person. It is found that the flow in the boundary layer around a person is able to a great extent to entrain and transport air from below the breathing zone. In the case of non-passive, heated contaminant sources, this entrainment improves the indoor air quality. Measurements of exposure due to a passive contaminant source show a significant dependence on the flow field as well as on the contaminant source location. Poor system performance is found in the case of a passive contaminant released in the lower part of the room close to the occupant. A personal exposure model for displacement ventilated rooms is proposed. The model takes the influence of gradients and the human thermal boundary layer into account. Two new quantities describing the interaction between a person and the ventilation are defined.     

Comparison of different decontaminant delivery methods for sterilizing unoccupied commercial airliner cabins

Effective decontamination is crucial if an airliner cabin is contaminated by biological contaminants, such as infectious disease viruses or intentionally released biological agents. This study used computational fluid dynamics (CFD) method as a tool and vaporized hydrogen peroxide (VHP) as an exemplary decontaminant and Geobacillus stearothermophilus spores as a simulant contaminant to investigate three VHP delivery methods for sterilizing two different airliner cabins. The CFD first determined the airflow and the transient distributions of the contaminant and decontaminant in cabins. Auxiliary equations were implemented into the CFD model for evaluating efficacy of the sterilization process. The improved CFD model was validated by the measured airflow and simulated contaminant distributions obtained from a cabin mockup and the measured efficacy data from the literature. The three decontaminant delivery methods were (1) to supply the mixed VHP and air through the environmental control system of a cabin, (2) to send mixed VHP and air through a front door and to extract them from a back door of a cabin, and (3) to send directly VHP to a cabin and enhance the mixing with air in the cabin by fans. The two air cabins studied were a single-aisle and a twin-aisle airliner one. The results show that the second decontaminant delivery method (displacement method) was the best because the VHP distributions in the cabins were most uniform, the sterilization time was moderate, and the corrosion risk was low. The method displaced the existing air by the air/disinfectant solution, rather than dispersive mixing as the other two methods.     

Indoor air environment: more structures to see?

A convection transport visualization technique is suggested to analyze the indoor air environment (IAE). A two-dimensional and laminar displacement ventilated room with discrete heat and contaminant sources is numerically investigated. Based on the governing equations, three convection transport functions, i.e. streamfunction, heatfunction, and massfunction, are derived to describe the fluid, heat, and contaminant transport processes, respectively. Main attentions are focused on the effects of the strength of heat source (Gr), the strength of contaminant source (Br), the strength of external ventilation (Re), and the positions of inlet/outlet openings on IAE. Numerical results illustrated that the abstract transport behaviors of the fluid, heat, and contaminant indoors are clearly exhibited by the convection transport functions which provides a simple but practical means of assessing IAE.