Article

Influence of cabin conditions on placement and response of contaminant detection sensors in a commercial aircraft

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Abstract

Potential causalities due to airborne disease transmission and risk of chem-bio terrorism in commercial airliner cabins can be reduced by fast responses. Fast responses are only possible by using sensors at appropriate locations in the cabins. Cost, size and weight factors restrict the number of sensors that could be installed inside a cabin. Since release locations and seating patterns of passengers can impact airborne contaminant transports, this study first addressed this impact by using a validated computational fluid dynamics (CFD) program in a four-row mockup of twin-aisle airliner cabin. It was observed that occupancy patterns and release locations have little influence on longitudinal contaminant transports though localized variations of contaminant concentrations may exist. The results show that response time of the sensors is considerably reduced with the increase in number of sensors. If only a single sensor is available across a cabin cross-section then it should be placed at the middle of the ceiling. A cabin model of a fully occupied twin-aisle airliner with 210 seats was also build to study the diverse contaminant distribution trends along cabin length. The results reveal that seating arrangements can make cross-sectional airflow pattern considerably asymmetrical. Similar airflow patterns make the longitudinal contaminant transport in the business and economy classes alike. The presence of galleys greatly affected the longitudinal transport of contaminants in a particular cabin section. The effects due to galleys were less significant if a multipoint sampling system was used. The multipoint sampling system can also reduce the number of sensors required in a cabin.

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... In all the studies so far, the conditions are basically the same where passengers are static, and the cabin is fully occupied. However other factors can influence the contaminant transport such as seats, galleys and toilet arrangement [138] or when a cabin crew is moving a cart along the aisle. Using a small scale model (KSU-767s) for experimental validation, Mazumdar et al. (2011) [139] concluded that the wake by cart movement could have transported the SARS-CoV-1 pathogen from the infected passenger to other passengers seated seven rows away. ...
... for the location of the sensors, several authors discussed the possibilities.Mazumdar et al. (2008), using uniform inlet boundary conditions, numerically studied the effect of contaminant release from near the mouth, hand, leg and seat back in front of the passenger, in different seats and 4 different seating patterns in a 4-row mockup and a full cabin model[138]. The following conclusions could be drawn:• If only one sensor can be pu ...
... for the location of the sensors, several authors discussed the possibilities.Mazumdar et al. (2008), using uniform inlet boundary conditions, numerically studied the effect of contaminant release from near the mouth, hand, leg and seat back in front of the passenger, in different seats and 4 different seating patterns in a 4-row mockup and a full cabin model[138]. The following conclusions could be drawn:• If only one sensor can be put, the best place is the center of the cabin ceiling. ...
Thesis
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To aid the prevention and mitigation of the next pandemic, aircraft cabins must be continuously designed to ventilate effectively any contaminant dispersed in the air, and eventually allowing the early detection of an event of pathogen spreading using bioaerosol sensors. A RANS simulation, employing a modified k-ε approach and involving a detailed diffuser geometry, was used to accurately simulate the complex behavior of the ventilation jets and compare the results obtained with available experimental data. The modified realizable k-ε model was validated using quantitative and qualitative methods for a half-row cabin. Subsequently, a contaminant was continuously injected into the center and side of the 3-row cabin, and ultimately conjugated with the use of gaspers. Briefly, it was found that, if gaspers are normal to the wall, the conjugated effect with the moist air flow vortex and thermal plume creates a condition of still air, thereby promoting diffusion and decreasing dispersion. Finally, either with gaspers turned on or off, the suggested locations for future sensors would be on the ceiling right above the passenger, and in the backseat surface of the front seat.
... Both models require knowledge of flow path descriptions, building geometry, weather and local shielding conditions, terrain roughness factors and mechanical ventilation system properties. Addressing the underlying assumption in most multizonal models, i.e., the assumption of well-mixed zones, and neglecting airflow momentum preservation, researchers proposed computational fluid dynamics (CFD), fast fluid dynamics, and combined multizone CFD methods [33][34][35][36][37][38] . One of the major drawbacks of using CFD methods is the simulation time, which makes CFD unfeasible for performing long-term dynamic simulations of a building with relatively complex structures. ...
... Computational fluid dynamics (CFD), fast fluid dynamics, and combined multizone CFD methods [33][34][35][36][37][38] All regions obey the law of conservation of mass, energy and momentum. ...
... Their values were taken from the minute-by-minute test results of portable weather stations during the AIR field test. 36 The building faces north. Swami & Chandra's wind pressure profile [62] for low-rise buildings was applied to calculate the wind coefficients for different zone facade. ...
Article
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Air infiltration through building envelopes has a considerable impact on the comprehensive performance of buildings, especially in terms of their energy demand and indoor air quality. Therefore, it is important to accurately predict building air infiltration rates under various scenarios. High airtightness is one of the typical characteristics of passive ultra-low energy buildings. With the rapid application of passive technology in building energy efficiency, the airtightness of new urban buildings has been significantly improved. The centralized air leakage path distribution assumption of current prediction model for building air infiltration rate is inconsistent with the actual situation of high airtightness buildings, which reduces its prediction accuracy and application range. Therefore, it is of great practical significance and academic value to carry out the research on the prediction model of air infiltration rate of buildings with high airtightness. This paper presents an air infiltration prediction model for single-zone buildings with adventitious openings. The building envelope was broken down into permeable parts and impermeable parts, and the air leakage pathways were assumed to be uniformly and continuously distributed in the permeable envelope. A linear pressure distribution over the building facade was assumed, and the airflow rate was integrated in the vertical and horizontal planes to theoretically predict the air infiltration rate. The feasibility of the proposed model was tested by comparing the air infiltration rates simulated by this model with those determined using the tracer gas attenuation method of an airtight building. The initial test results suggest that this model is mathematically robust and is capable of modeling the air infiltration of a building in a wide variety of scenarios. Reasonable agreement was found between the tested and simulated results. This study can provide basic theoretical support for the coupling performance analysis of high airtightness buildings.
... The seat layout exerts an impact on the cabin geometry and thus may affect the formed cabin airflow therein. Most previous studies adopted a simplified seat geometry [9][10][11][12][13][14][15][16], in which the seat cushion was horizontal and the seatback was upright. Realistic aircraft seats were also used in some studies, which captured more details of the streamlined profiles of the seats [4,[17][18][19][20][21][22][23][24][25]. ...
... Realistic aircraft seats were also used in some studies, which captured more details of the streamlined profiles of the seats [4,[17][18][19][20][21][22][23][24][25]. The adopted manikins varied greatly, ranging from heated rectangular boxes [11,[13][14][15][16]20,21], to models with realistic body profiles [4,9,10,12,[17][18][19]22]. Table 1 summarizes the seat structure and manikins in the published studies, in which the seat layouts and manikins were symmetric. ...
... In a half-occupied, twin-aisle cabin mockup, the airflow was found to be asymmetric because of the asymmetric air supply velocity profiles and also the asymmetric manikin occupation mode [14,15]. In a twin-aisle airliner cabin, the seating patterns of passengers were reported to exert a significant impact on the localized airflow and contaminant transport [16]. The airflow in a single-aisle cabin with five passengers in each row (3 passengers + 2 passengers) was found to be asymmetric due to the asymmetric cabin geometry [22]. ...
Article
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Airborne pollutant transport in an aircraft cabin is greatly affected by the created airflow. The seat layout can impact the flow and thus the pollutant transport. Most studies have adopted symmetric upright seats for simplicity. The influence of seat inclination and seat misalignment on airflow and pollutant transport is still unclear. This investigation adopted a validated computational fluid dynamics (CFD) method to study the airflow and airborne pollutant distribution in a single-aisle cabin with seven rows of seats. The pollutant was assumed to be released from a passenger seated in the middle of three adjacent seats. A total of five different seat layouts were considered, including all of the upright seats, the inclination of three adjacent seats, the inclination of all of the seats in half a cabin, the inclination of all of the seats in a whole cabin, and the misalignment seat rows across the aisle. The flows in both the cross and longitudinal sections were compared. The pollutant concentrations in the respiratory zone of the passengers in different seats were adopted to evaluate the cross-contamination. The results revealed that the symmetric seat layout aids to circumscribe the released pollutant in a small region and reduces the cross-contamination either by maintaining the upright seats or inclining all of the seats. Contrarily, any inclination of seats or a misalignment of seat rows should be avoided during the pandemic since an asymmetric seat layout would generate asymmetric flow and strengthen the spreading of pollutants.
... Other examples include optimal sensor location for aircraft cabins starting from a set of initial sensor locations and a set of release scenarios [26]. General recommendations for sensor locations for an aircraft cabin have been given in Ref. [27]. The applicability of inverse methods for advection-diffusion problems have been recently reviewed [28]. ...
... The source contaminant concentration [27] did not consider the outlet as an option to place the sensor. Using the sensor placement algorithm provided in this paper, a single sensor as well as 2 sensors are considered. ...
... In this appendix a sensor is placed based on the methodology in this paper using a published Markov matrix [40] and compared with general recommendations from literature [27,49]. The non-zero entries of the Markov matrix from C. Chen et al., 2014 [40] are shown in Fig. 3. ...
Article
Air quality has been an important issue in public health for many years. Sensing the level and distributions of impurities help in the control of building systems and mitigate long term health risks. Rapid detection of infectious diseases in large public areas like airports and train stations may help limit exposure and aid in reducing the spread of the disease. Complete coverage by sensors to account for any release scenario of chemical or biological warfare agents may provide the opportunity to develop isolation and evacuation plans that mitigate the impact of the attack. All these scenarios involve strategic placement of sensors to promptly detect and rapidly respond.
... Computational Fluid Dynamics (CFD) models provide a means to study concentration and deposition profiles at high spatial and temporal resolutions in aircraft cabin environments (Poussou et al., 2010;Rai and Chen, 2012;Liu et al., 2012). The CFD model in this study was developed based on previously evaluated approximations for flow modeling and contaminant transport in aircraft cabins (Mazumdar and Chen, 2008;Mazumdar et al., 2011;Poussou et al., 2010), with specific focus on spatial variability of pesticide concentrations and depositions across the cabin when passengers are directly exposed to the sprayed pesticide. The model was evaluated using data from controlled experiments conducted in a cabin mockup facility. ...
... Ventilation was modeled via two overhead linear inlets at the center of the cabin and via two linear outlets located near the side walls at floor level. The cabin model is based on the approach used by Mazumdar and Chen (2008), customized for the geometry of the cabin mockup. For all 77 passengers, surfaces such as the lap of the passengers, passengers (whole body), top of seats and back of seats were represented as separate surfaces so that the concentrations for each type of surface can be directly extracted without requiring interpolation in post processing. ...
... The 29 ACH case (1400 cubic feet min −1 ) corresponds to the typical operating flow rate of the mockup, while the 1 ACH case (48 cubic feet min −1 ) was an approximation of the mockup operation with forced ventilation turned off. The thermal boundary conditions during the experiments were also not measured and hence the CFD model used the boundary conditions presented in Table 1 which are similar to that used by Mazumdar and Chen (2008). In short, a temperature boundary condition was used for all surfaces, which limits unrealistic rise in temperature under low ventilation rates. ...
Article
Spraying of pesticides in aircraft cabins is required by some countries as part of a disinsection process to kill insects that pose a public health threat. However, public health concerns remain regarding exposures of cabin crew and passengers to pesticides in aircraft cabins. While large scale field measurements of pesticide residues and air concentrations in aircraft cabins scenarios are expensive and time consuming, Computational Fluid Dynamics (CFD) models provide an effective alternative for characterizing concentration distributions and exposures. This study involved CFD modeling of a twin-aisle 11 row cabin mockup with heated manikins, mimicking a part of a fully occupied Boeing 767 cabin. The model was applied to study the flow and deposition of pesticides under representative scenarios with different spraying patterns (sideways and overhead) and cabin air exchange rates (low and high). Corresponding spraying experiments were conducted in the cabin mockup, and pesticide deposition samples were collected at the manikin's lap and seat top for a limited set of five seats. The CFD model performed well for scenarios corresponding to high air exchange rates, captured the concentration profiles for middle seats under low air exchange rates, and underestimated the concentrations at window seats under low air exchange rates. Additionally, both the CFD and experimental measurements showed no major variation in deposition characteristics between sideways and overhead spraying. The CFD model can estimate concentration fields and deposition profiles at very high resolutions, which can be used for characterizing the overall variability in air concentrations and surface loadings. Additionally, these model results can also provide a realistic range of surface and air concentrations of pesticides in the cabin that can be used to estimate potential exposures of cabin crew and passengers to these pesticides.
... Furthermore, in-flight airflow studies using full-scale laboratory mockups are expensive and time consuming. Varying cabin conditions such as different occupancy distributions, passenger capacities, and movements of crew and passengers [36,37] would make laboratory measurements more complicated. Hence, cheaper and more efficient computer simulations seem more preferable for airflow studies in airliner cabins. ...
... Despite there being some uncertainties in the models, requiring sufficient knowledge of fluid mechanics on the part of a user, and demanding a high capacity computer, CFD has become the most widely used tool for studying air distributions in airliner cabins due to the rapid increase in computer capacity and the development of user-friendly CFD program interfaces. Examples can be found in [9,11,15,19,21,24,25,27,35,37,[44][45][46][47][48][49][50][51][52]. The CFD models used were Reynolds Averaged Navier-Stokes equation (RANS) models and Large Eddy Simulation (LES). ...
... This effort can reduce the experimental costs and make the CFD simulation more reliable. [16] (a) With a VPTV by Wang et al. [37] (b) With a PIV by Bosbach et al. [38] ...
Article
Air distributions in commercial airliner cabins are crucial for creating a thermally comfortable and healthy cabin environment. This paper reviews the methods used in predicting, designing, and analyzing air distributions in the cabins, among which experimental measurements and numerical simulations are the two popular ones. The experimental measurements have usually been seen as more reliable although they are more expensive and time consuming. Most of the numerical simulations use Computational Fluid Dynamics (CFD) that can provide effectively detailed information. Numerous applications using the two methods can be found in the literature for studying air distributions in aircraft cabins, including investigations on more reliable and accurate models. The review in the paper shows that the studies using both experimental measurements and computer simulations are becoming popular. And it is necessary to use a full-scale test rig to obtain reliable and high quality experimental data. What’s more, the hybrid CFD models are found to be rather promising for simulating air distributions in airliner cabins.
... The maximum width of the cabin was 4.72 m, the maximum height was 2.10 m, and the aisle width was 0.48 m. The passengers in the cabin were portrayed by 28 box-shaped mannequins, and the total surface area of a mannequin was about 1.8 m 2 [26]. The mixing type of air distribution system was considered in this study. ...
... Computation 2024, 12, x FOR PEER REVIEW 3 of 12 height was 2.10 m, and the aisle width was 0.48 m. The passengers in the cabin were portrayed by 28 box-shaped mannequins, and the total surface area of a mannequin was about 1.8 m 2 [26]. The mixing type of air distribution system was considered in this study. ...
Article
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Aircraft cabins have high occupant densities and may introduce the risk of COVID-19 contamination. In this study, a segment of a Boeing 767 aircraft cabin with a mixing type of air distribution system was investigated for COVID-19 deposition. A section of a Boeing 737-300 cabin, featuring four rows with 28 box-shaped mannequins, was used for simulation. Conditioned air entered through ceiling inlets and exited near the floor, simulating a mixed air distribution system. Cough droplets were modeled using the Discrete Phase Model from two locations: the centre seat in the second row and the window seat in the fourth row. These droplets had a mean diameter of 90 µm, an exhalation velocity of 11.5 m/s and a flow rate of 8.5 L/s. A high-quality polyhedral mesh of about 7.5 million elements was created, with a skewness of 0.65 and an orthogonality of 0.3. The SIMPLE algorithm and a second-order upwind finite volume method were used to model airflow and droplet dynamics. It was found that the ceiling accounted for the maximum concentration followed by the seats. The concentration of deposits was almost 50% more when the source was at window as compared to the centre seat. The Covid particles resided for longer duration when the source was at the centre of the cabin than when it was located near the widow.
... The gases in closed cabins can be identified quickly by the electronic nose and it is not necessary to classify all volatile compounds one by one. In the electronic nose detection process, in this case, the volatile compounds are converted into electronic signals in the form of digital outputs of the electronic nose sensor array [51]. Electronic noses enable realtime detection of air in closed cabins and do not require a complex sample pre-treatment, making them well suited for air detection in closed cabins. ...
... By assuming different pollutant release rates and sensor sensitivities, it was found that the optimal location for the sensor was in the middle of the ceiling. Similarly, Mazumdar (2008) [27] used the commercial CFD program FLUENT to study the influence of seat type and pollution source location on the placement and response of pollutant detection sensors in the cabin of dual-aisle commercial aircraft. The results show that the number of sensors is linearly related to the detection speed. ...
Article
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Gas detection in enclosed cabins is a challenging concern in the industry to ensure the safety of cabin operations and personnel driving. There has been a growing development in the detection of safety in enclosed cabin operations based on volatile organic compounds, which have unique characteristics. The air pollution in closed cabins seriously affects the driver’s health, and the accuracy of the detection directly affects the operation safety of the cabin. However, until today, gas detection in enclosed cabins has relied on traditional methods that are expensive and time-consuming, and it cannot be detected in real time. This paper focuses on the potential and capability of electronic nose applications for gas detection in enclosed cabins. Since the electronic nose is a good substitute for the closed cabin, people’s attention to it has increased greatly. The characteristics of hazardous gas and warning gas in closed cabins are also discussed. In addition, this paper provides important insights into the challenges and future trends of the electronic nose, a low-cost, high-precision, and fast detection method, in more applications in closed compartments.
... There are two commonly used methods to simulate the aerosol systems with virus particles, or virus-carrying particles. One is to treat the system as one continuous substance and use Euler's method to solve a convective diffusion equation to obtain the virus concentration and distribution [14][15][16]. The other is to treat solid particles or droplets as a discrete phase material and use the Lagrangian's method to calculate the motion characteristics of each particle [14][15][16]. ...
... One is to treat the system as one continuous substance and use Euler's method to solve a convective diffusion equation to obtain the virus concentration and distribution [14][15][16]. The other is to treat solid particles or droplets as a discrete phase material and use the Lagrangian's method to calculate the motion characteristics of each particle [14][15][16]. Some in-cabin studies use the discretization method to obtain the trajectory of virus particles [4,17,18]. ...
Article
Full-text available
Passengers carrying the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a commercial aircraft cabin may infect other passengers and the cabin crew. In this study, a cabin model of the seven-row Airbus A320 aircraft is constructed and meshed for simulating the SARS-CoV-2 spread in the cabin with a virus carrier using the Computational Fluid Dynamics (CFD) modeling tool. The passengers’ infection risk is also quantified with the susceptible exposure index (SEI) method. The results show that the virus spreads to the ceiling of the cabin within 50 s of the virus carrier’s normal breathing. Coughing makes the virus spread to the front three rows with a higher mass fraction. While the high mass fraction areas always stay on the same side of the aisle as the virus carrier, the adjacent passengers and the passengers in the back two rows are affected more than the others when the virus carrier breathes normally. Spread patterns under the carrier’s two breath conditions, normal breath and cough, were numerically simulated.
... Mazumdar and Chen [17] and Zhang and Chen [18], highlight the importance of pollutant accumulation in confined spaces and of evaluating air quality close to the pollutant source. When the breath is the pollutant source, the zone that characterizes it is designated BZ, for "Breathing Zone". ...
... A replica of the CQ was built for this study (Fig. 1 a). The dimensions of the CQ and its ventilation system were extracted from its design documents [5,36,37], and the dimensions of the standard racks on the ISS [17]. The plywood walls were covered with layers of the same materials used as on the ISS for acoustic and radiation isolation purposes (NOMEX and Kevlar [18]). ...
... Mazumdar and Chen [17] and Zhang and Chen [18], highlight the importance of pollutant accumulation in confined spaces and of evaluating air quality close to the pollutant source. When the breath is the pollutant source, the zone that characterizes it is designated BZ, for "Breathing Zone". ...
... A replica of the CQ was built for this study (Fig. 1 a). The dimensions of the CQ and its ventilation system were extracted from its design documents [5,36,37], and the dimensions of the standard racks on the ISS [17]. The plywood walls were covered with layers of the same materials used as on the ISS for acoustic and radiation isolation purposes (NOMEX and Kevlar [18]). ...
Article
In poorly ventilated confined spaces, assessing the accumulation of CO2 in the breathing zone (BZ) is important evaluating human safety. The current study presents an experimental and numerical investigation of the CO2 generation rate and spatial distribution in the crew quarters (CQ) of the International Space Station. In microgravity, density-difference based airflow is nonexistent, and CO2 accumulates around the astronaut's head if the BZ is poorly or not at all ventilated. The aim is to study the breath's influence on CO2 spatial distribution in order to circumscribe the region that needs to be ventilated in the CQ. An experimental setup was used to measure the CO2 generation rate of several test subjects on Earth in a non-ventilated full-scale model of the CQ. The experimental CO2 results were used to validate CFD simulations of the CQ with gravity, with a human model inside featuring a full respiratory cycle. The validated CFD model was then used without gravity for a CO2 accumulation study. The respiratory cycle was analyzed in order to propose a rigorous definition of the BZ based on a frequency analysis of the breath. Results show that CO2 concentrations in the identified BZ are greater in the absence of gravity compared to a similar situation with gravity. It is believed that the ventilation system presently in place in the CQ does not effectively ventilate this strategic area, therefore a personalized ventilation type solution should be studied in the future.
... To reduce the computing time, many researchers have performed the flow simulations in parallel on multi-processor computers [9,10]. It is also possible to speed up the FFD simulation by running it in parallel on multi-processor computers. ...
... Solving equation (9), one can obtain P. Substituting P into equation (7), U i will be known. ...
Article
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Fast indoor airflow simulations are necessary for building emergency management, preliminary design of sustainable buildings, and real-time indoor environment control. The simulation should also be informative since the airflow motion, temperature distribution, and contaminant concentration are important. Unfortunately, none of the current indoor airflow simulation techniques can satisfy both requirements at the same time. Our previous study proposed a Fast Fluid Dynamics (FFD) model for indoor flow simulation. The FFD is an intermediate method between the Computational Fluid Dynamics (CFD) and multizone/zonal models. It can efficiently solve Navier–Stokes equations and other transportation equations for energy and species at a speed of 50 times faster than the CFD. However, this speed is still not fast enough to do real-time simulation for a whole building. This paper reports our efforts on further accelerating FFD simulation by running it in parallel on a Graphics Processing Unit (GPU). This study validated the FFD on the GPU by simulating the flow in a lid-driven cavity, channel flow, forced convective flow, and natural convective flow. The results show that the FFD on the GPU can produce reasonable results for those indoor flows. In addition, the FFD on the GPU is 10–30 times faster than that on a Central Processing Unit (CPU). As a whole, the FFD on a GPU can be 500–1500 times faster than the CFD on a CPU. By applying the FFD to the GPU, it is possible to do real-time informative airflow simulation for a small building.
... Into the post-Moore era, sustained software acceleration requires contributions from parallelism and compiler optimizations (Schardl 2016). Parallel computing with Central Processing Unit (CPU) is the most commonly used technique in building simulations, such as computational fluid dynamics for building environments (Mazumdar and Chen 2008), and building energy simulations (Hopkins et al. 2011). However, purchasing and maintaining supercomputers is often prohibitively expensive for most small businesses in the building industry (Zuo et al. 2014). ...
Article
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Indoor glare significantly affects the visual comfort and health of occupants, daylighting simulation can act as an effective method to analyze daylight glare issues during building design. To address the extensive computational costs associated with calculating annual daylight glare metrics with existing methods, this study introduces an acceleration framework, which can be widely applied. The framework integrates a newly developed daylight matrix multiplication program (DMM4GPU) for Graphics Processing Unit (GPU) computation acceleration and the previously developed Accelerad program, which can accelerate the calculation of Daylight Coefficient (DC) matrices in the Two-phase Method (2-PM), the View matrices in the Three-phase Method (3-PM) and Five-phase Method (5-PM). By comparing with standard Radiance Central Processing Unit (CPU) calculations, the study validated the acceleration framework’s simulation accuracy and significantly reduced computation time in daylight glare metrics calculations. It also analyzed the impact of various simulation parameters on the framework’s performance. Results indicate that the acceleration framework’s error in calculating Daylight Glare Probability (DGP) is minimal (RMSE < 0.004), and the computation times for the 2-PM, 3-PM, and 5-PM are reduced by 94.8%, 93.9%, and 83.0%, respectively. Furthermore, this study discussed modeling techniques to avoid possible errors in the daylight GPU computations.
... In addition, the standing positions may be random rather than symmetrical in the cab. Previous investigations [62,63] have found that the asymmetric geometry may lead to asymmetric airflow and the crosstransport of pollutants. Therefore, future investigations should examine the influence of different random standing postures on the airflow and particle transmission. ...
Article
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People in cities use elevators daily. With the COVID-19 pandemic, there are more worries about elevator safety, since elevators are often small and crowded. This study used a proven CFD model to see how the virus could spread in elevators. We simulated five people taking in an elevator for two minutes and analyzed the effect of different factors on the amount of virus that could be inhaled, such as the infected person's location, the standing positions of the persons, and the air flow rate. We found that the position of the infected person and the direction they stood had a big impact on virus transmission in the elevator. The use of mechanical ventilation with a flow rate of 30 ACH (air changes per hour) was effective in reducing the risk of infection. In situations where the air flow rate was 3 ACH, we found that the highest number of inhaled virus copies could range from 237 to 1186. However, with a flow rate of 30 ACH, the highest number was reduced to 153 to 509. The study also showed that wearing surgical masks decreased the highest number of inhaled virus copies to 74 to 155.
... The integration of CFD simulations into the design process for design evaluation and optimization significantly ensures the quality and comfort of the design (Spengler and Chen, 2000;Mochida et al., 2002;Jiang et al., 2003). CFD software, such as ANSYS Fluent (ANSYS, 2021), OpenFOAM (Jasak et al., 2007), and CHAM PHOENICS (CHAM, 2021), require high computer resources during installation and computation, which is an additional burden for architects (Mazumdar and Chen, 2008;Zuo and Chen, 2009). As light-version CFD tools, CFD plug-ins require significantly fewer computer resources than CFD software (Han et al., 2018). ...
Article
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The transformation of urban and building design into green development is conducive to alleviating resource and environmental problems. Building design largely determines pollutant emissions and energy consumption throughout the building life cycle. Full consideration of the impact of urban geometries on the microclimate will help construct livable and healthy cities. Computational fluid dynamics (CFD) simulations significantly improve the efficiency of assessing the microclimate and the performance of design schemes. The integration of CFD into design platforms by plug-ins marks a landmark development for the interaction of computer-aided design (CAD) and CFD, allowing architects to perform CFD simulations in their familiar design environments. This review provides a systematic overview of the classification and comprehensive comparison of CFD plug-ins in Autodesk Revit, Rhinoceros/Grasshopper, and SketchUp. The applications of CFD plug-ins in urban and building design are reviewed according to three types: single-objective, multi-objective, and coupling simulations. Two primary roles of CFD plug-ins integrated into the design process, including providing various micro-scale numerical simulations and optimizing the original design via feedback results, are analyzed. The issues of mesh generation, boundary conditions, turbulence models, and simulation accuracy during CFD plug-in applications are discussed. Finally, the limitations and future possibilities of CFD plug-ins are proposed.
... Y. Fu et al [18] proposed a greedy thermal sensor placement algorithm to arrange the thermal sensors in the chip. The position optimization of the sensor can also be realized by using hydrodynamic simulation [19], [20], [21]. M. L. H. Loong applied the fuzzy logic simulation to obtain the best location for sensor installation with the most faults detected [22]. ...
Article
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The arrangement of temperature sensors in most existing large-scale laying hen houses is random or placed according to the experience of breeders. However, this can’t achieve accurate monitoring of the henhouse. The temperature in the laying hen houses cannot be uniformly controlled, leads to the reduction of production efficiency of laying hens. In this paper, aiming at the placement of temperature sensors in laying hens’ houses, a placement optimization method was proposed. Firstly, the correlation coefficient of sensors is calculated to eliminate redundant sensors. Then, all the remaining sensors are arranged and combined. Finally, taking the grey correlation degree of each combination as the objective function, the dual-structure coding genetic algorithm is used to optimize the sensor combination. The strategy was tested in a large hen house. When the initial deployment of 81 sensors is reduced to at least 3, the established target can still be achieved, and the position of the target sensor can be calculated. This strategy not only meets the goal of accurately monitoring the hen house temperature, but also saves the hardware cost, which has important application value.
... The aisle width was 0.48 m. As stated by Topp et al. [22], a box designed dummy is well enough for the investigation of total airflow in the zone and several previous studies utilized a box designed mannequins [21,23,24]. Hence, a box designed mannequins were utilized in this work to designate 28 passengers in the aircraft cabin. ...
Article
Airliner passengers are more and demanding in terms of thermal comfort. But it is not yet easy for crew to control the environment control system (ECS) that satisfies the thermal comfort for most travelers due to a number of reasons. It is, therefore, essential to develop the existing design of air circulation system for aircraft cabins. This work proposed six innovative personalized ventilation systems (PVSs) that would maintain thermal comfort to improve the cabin micro-environment. This study first validated a Computational Fluid Dynamics (CFD) program with the experimental data of airflow and air temperature from an environmental chamber. Then the validated CFD program was used to calculate the air velocity, air temperature, relative humidity (RH) and examined the thermal comfort in a section of Boeing 767 aircraft cabin with the six innovative PVSs. By comparing the six PVSs in terms of relative humidity, velocity, temperature, predicted mean vote (PMV), predicted percentage dissatisfaction (PPD) and age of air (AoA), this study found that the proposed systems provided an acceptable thermal environment aircraft cabin. The personal outlets configuration at both sides of the passenger head (PVS-1) was the best; it can improve the RH by 12% without the risk of air drafts, and it also has a standard PMV (0.2) and PPD (<15%) range.
... In this study the aerosol transport and trajectory in an air-conditioned space was proposed as a threedimensional, transient, turbulent, multiphase CFD model. The Eulerian-Lagrangian 35,36 method was used to model gas-liquid two-phase flow, for the liquid phase being as discrete phase model (DPM, liquid injection of saliva droplet) and the gas phase being the continuous phase. The gas phase has two components: air and water vapour, while the liquid phase is aerosol droplets, which was realistically modelled by defining its components, size distribution and volatility. ...
Article
Aerosol generated from a human cough can be a potential major indoor health risk due to the possible transmission of infectious respiratory diseases to surrounding individuals within the same room and even could spread out via air-ventilation/conditioning systems. This study aims to investigate the transport characteristics and trajectory of coughed aerosols under the influence of conditioned air ventilation as well as near-by human breathing zone using computational fluid dynamics (CFD). An experimental system consisting of air-conditioned space with multiple inlets and outlets, a cough simulator and a receiver was built to validate the CFD predictions. The comparison is in good agreement. The CFD model was established as a transient three-dimensional multiphase multicomponent Eulerian–Lagrangian model and numerically solved using commercial software ANSYS Fluent. Both gas and liquid phases were modelled as multicomponent mixtures. With this CFD model, the indoor transport and trajectory of coughed aerosols can be accounted for the distributions of portions inhaled by each manikin, deposited on surfaces of manikins and chamber walls, as well as recirculated back into the ventilation system. Results reveal that the aerosol source location and the ambient air movement can be crucial factors of aerosol trajectory in terms of direct and indirect influence.
... The gas phase has two components air and water vapor, while the liquid phase is aerosol liquid, which is sophisticatedly modelled by defining its components, size distribution, evaporative or non-evaporative to match the real situation. To simulate the aerosol, both Eularian [20] and Lagrangian [21] approaches are employed. The former is for the component concentration of gas phase, while the latter is for the transport pattern of liquid phase. ...
... In order to accelerate the CFD simulation, some researchers (Beghein et al. 2005;Crouse et al. 2002;Mazumdar and Chen 2008) used multi-processor supercomputers or computer clusters. The speed was much faster but this approach required expensive computing facilities, a space for installing the computer, and a large cooling system to cool the computer (Feng and Hsu 2004). ...
Conference Paper
Full-text available
In case of fire in buildings, real-time or faster-than-real-time simulations of airflow and smoke transport can reduce casualties. The simulations should be informative by providing airflow motion, temperature distribution and smoke concentration. By solving the Navier-Stokes equations and transportation equations for energy and smoke, Fast Fluid Dynamics (FFD) model can provide detailed information. If the computation is performed on a Graphics Processing Unit (GPU), the FFD simulation can be faster-than-real-time for a moderate size building with 10 7 grids and ∆t = 0.1s.
... A traditional method to accelerate the flow simulation is to use multi-processor computers [4,5], but the cost is very high. It is not only expensive to purchase the hardware and software but also to find a suitable space for installing and cooling the computers [6]. ...
Conference Paper
Full-text available
To design a comfortable and safe indoor environment, it is crucial to know the distributions of air velocity, air temperature and contaminant concentrations in the indoor space. The distributions can be obtained by computer simulations, such as Computational Fluid Dynamics (CFD). However, the CFD requires intensive computing efforts to solve the Navier-Stokes equations, energy equation and species concentration equations. If the computing domain is as large as a building, the computing time on a single Central Processor Unit (CPU) will become too long for most design applications. Parallelized computing on multiprocessor-computers can reduce the computing time, but the costs of such computers and their maintenance is prohibitively high for many users. Hence, it is essential to seek an alternative to speed up the CFD calculations and to reduce the computing costs. This investigation performed flow simulations in parallel on a graphics process unit (GPU). A GPU consists of hundreds of processors, which offers a great power for parallel computing. The price of a GPU is less than $1,000 and it has almost no maintenance cost. A Fast Fluid Dynamics (FFD) model was implemented on the GPU. The FFD solves the Navier-Stokes equations as the CFD does. By scarifying some accuracy, the FFD can be about 50 times faster than the CFD with the same numerical settings. Our results show that the FFD simulations on the GPU can provide the same results as those on the CPU, but the GPU version is up to 30 times faster than the CPU version. As a result, it is possible to perform real-time simulations of airflow in a moderate size building by using the FFD on the GPU. Meanwhile, this study indicates that the GPU can be also used to accelerate other scientific computing, such as CFD simulations.
... In order to accelerate the CFD simulation, many researchers, such as Crouse et al. (2002) and Mazumdar and Chen (2008), executed simulations in parallel on multi-CPU computers. The parallel computing can greatly reduce the computing time. ...
Conference Paper
Full-text available
Computational fluid dynamics (CFD) can provide detailed information of flow motion, temperature distributions and species dispersion in buildings. However, it may take hours or days, even weeks to simulate airflow in a building by using CFD on a single central processing unit (CPU) computer. Parallel computing on a multi-CPU supercomputer or computer cluster can reduce the computing time, but the cost for such high performance computing is prohibitive for many designers. Our paper introduces high performance parallel computing of the airflow simulations on a graphics processing unit (GPU). The computing time can be reduced by 10-30 times using the GPU. Furthermore, the cost of purchasing such a GPU is only $500, which is less than 2% of a multi-CPU supercomputer or a computer cluster for the same performance.
... The optimization based techniques has been successfully used for a wide variety of sensor placement scenarios [15][16][17][18][19] using both CFD or zonal simulations. While these methods account for the effects of flow fields in the sensor placement process, challenges include computational difficulties in finding the optima. ...
Preprint
Sensors in buildings are used for a wide variety of applications such as monitoring air quality, contaminants, indoor temperature, and relative humidity. These are used for accessing and ensuring indoor air quality, and also for ensuring safety in the event of chemical and biological attacks. It follows that optimal placement of sensors become important to accurately monitor contaminant levels in the indoor environment. However, contaminant transport inside the indoor environment is governed by the indoor flow conditions which are affected by various uncertainties associated with the building systems including occupancy and boundary fluxes. Therefore, it is important to account for all associated uncertainties while designing the sensor layout. The transfer operator based framework provides an effective way to identify optimal placement of sensors. Previous work has been limited to sensor placements under deterministic scenarios. In this work we extend the transfer operator based approach for optimal sensor placement while accounting for building systems uncertainties. The methodology provides a probabilistic metric to gauge coverage under uncertain conditions. We illustrate the capabilities of the framework with examples exhibiting boundary flux uncertainty.
... Flow boundary conditions for the sources of droplet when CFD method is chosen to simulate the particle transport in an enclosed environment. The Lagrangian method is usually used to track the particle paths, while the Eulerian method is for predicting the particle concentration distribution [14][15][16]. Herein, the Eulerian method is adopted to deal with the droplet concentration spread in the aircraft cabin, the convection-diffusion equation is coupled with Navier-Stokes equations and turbulence model to simulate the droplet concentration spread in civil aircraft cabin. The main purpose of this paper is to investigate the Environmental Control System (ECS) influences on the virus concentration spread in longitudinal and transverse directions. ...
... While the former approach is fast, challenges of this approach include the lack of a formal methodology to rationally design response time, ensuring full/partial coverage of the indoor environment, and challenges to generalizing the approach for multiple rooms or zones (Liu and Zhai, 2009b) and accounting for uncertainty in the flow field. This has resulted in the increased popularity of the latter approach (Liu and Zhai, 2009a;Mazumdar and Chen, 2008;Zhang and Chen, 2007;Chen and Wen, 2008;Zhou and Haghighat, 2009). However, most current optimization/inverse approaches have their own challenges that preclude widespread usage. ...
Conference Paper
Sensors are an integral part of buildings to sense pollutants ,identifying extreme events and for maintaining comfort. Traditionally identification of the sensor locations is via solution of inverse problem (computationally intensive) or using some standard thumb rules which might not be suitable for every building. In recent years,the concepts of non-linear control theory is integrated with fluid dynamics to develop Perron-Frobenious(PF) operator based approaches to design sensor placement strategies. This approach alleviates the shortcomings of the previous approaches. The current paper extends PF framework to account for uncertainty of airflow in the building to compute more robust sensor location maps. The developed approach is demonstrated for a IEA-2D benchmark problem. The algorithm is easily extensible to the complex buildings and can account for various uncertain situations.
... Parallel computing with multi-CPUs on supercomputers is the most commonly used parallel technology in building simulation. The examples are computational fluid dynamics for indoor environment (Mazumdar, 2008, Hasama, 2008, uncertainty and sensitivity decomposition of building energy models (Eisenhower, 2011), and massive building energy simulations (Hopkins, 2011). However, purchasing and maintaining the supercomputers is usually too expensive for small businesses that make up the majority of the building industry. ...
Article
Full-text available
Building designers are increasingly relying on complex fenestration systems (CFS) to reduce energy consumed for lighting and HVAC in low-energy buildings. Radiance, a lighting simulation program, has been used to conduct daylighting simulations for CFS. Depending on the configurations, the simulation can take hours or even days using a personal computer. This paper describes how to accelerate the matrix multiplication portion of a Radiance three-phase daylight simulation by conducting parallel computing on heterogeneous hardware of a personal computer. The algorithm was optimized and the computational part was implemented in parallel using OpenCL. The speed of the new approach was evaluated using various daylighting simulation cases on a multi-core central processing unit (CPU) and a graphics processing unit (GPU). Based on the measurements and analysis of the time usage for the Radiance daylighting simulation, further speedups can be achieved using fast input/output devices and storing the data in a binary format.
... Since increasing the clock rate alone cannot meet the rapidly growing demands on computing power, it is more feasible to compute in parallel on multiple processors. Parallel computing on supercomputers is already widely used in other industries and there are also a few applications in building industry (Wenisch et al. 2007, Hasama et al. 2008, Mazumdar and Chen 2008. However, purchasing and maintaining supercomputers is usually too expensive for small businesses that make up the majority of the building industry. ...
Article
Full-text available
We report on the acceleration of annual daylighting simulations for fenestration systems in the Radiance ray-tracing program. The algorithm was optimized to reduce both the redundant data input/output operations and the floating-point operations. To further accelerate the simulation speed, the calculation for matrix multiplications was implemented using parallel computing on a graphics processing unit. We used OpenCL, which is a cross- platform parallel programming language. Numerical experiments show that the combination of the above measures can speed up the annual daylighting simulations 101.7 times or 28.6 times when the sky vector has 146 or 2306 elements, respectively.
... Both Euler-Euler model and Euler-Lagrange model can be used to compute cough particle transport in CFD simulations ). However, Euler-Euler model is usually utilized to forest particle concentration distribution (Mazumdar and Chen 2008;Yan et al. 2009). Euler-Lagrange model is usually used to determine particle dispersion pattern Zhang and Chen 2006). ...
Article
Full-text available
Air distribution system is very important to indoor air quality (IAQ) in China railway high-speed (CRH) train cabin. Air distribution systems in three different CRH train cabins are simulated and evaluated in this paper by using the computational fluid dynamic (CFD) method. CFD models of CRH1, CRH2 and CRH5 train cabins are developed and validated basing on the field experiments in three train cabins. Flow field, temperature field, and airflow pattern in the three train cabins are investigated respectively by using the CFD models developed. Four improved performance indexes which can eliminate influences of geometric dimension are utilized to evaluate the air distribution systems in the cabins. The cough droplets dispersion processes inside the CRH train cabins are simulated to investigate the cough droplets removal ability. Simulation results show that good airflow pattern is very critical to guarantee the uniform distribution of flow field, temperature field and thermal comfort in the train cabin. The air distribution system employed in CRH5 train cabin is the most efficient among the three train cabins. Moreover, CRH5 train cabin has stronger cough droplets removal ability than CRH1 and CRH2 train cabins. Air distribution system in CRH5 train cabin should be adopted in the next generation CRH train cabin in the future.
... legs). This velocity field is in qualitative agreement with Mazumdar and Chen (2008) for a Boeing 767 ventilated cabin. ...
Article
Full-text available
The air ventilation system in wide-body aircraft cabins provides passengers with a healthy breathing environment. In recent years, the increase in global air traffic has amplified contamination risks by airborne flu-like diseases and terrorist threats involving the onboard release of noxious materials. In particular, passengers moving through a ventilated cabin may transport infectious pathogens in their wake. This paper presents an experimental investigation of the wake produced by a bluff body driven through a steady recirculating flow. Data were obtained in a water facility using particle image velocimetry and planar laser induced fluorescence. Ventilation attenuated the downward convection of counter-rotating vortices produced near the free-end corners of the body and decoupled the downwash mechanism from forward entrainment, creating stagnant contaminant regions.
... To monitor air quality and environmental parameters in an airliner cabin it is necessary to place sensors, which are often bulky and expensive. The study of the optimal sensor placement was faced by Zhang et al. [34] and Mazumdar et al. [35] who showed that the best location for a sensor is in the middle of the ceiling even if, to effectively detect contaminants, multipoint sampling systems for each row should be used because they can reduce the number of sensors required in the cabin. Moreover, also the practicality of using wireless sensors in airliner cabins was verified [36]. ...
... In order to accelerate the CFD simulation, many researchers, such as Crouse et al. (2002) and Mazumdar and Chen (2008), executed simulations in parallel on multi-CPU computers. The parallel computing can greatly reduce the computing time. ...
Article
Full-text available
Computational fluid dynamics (CFD) can provide detailed information of flow motion, temperature distributions and species dispersion in buildings. However, it may take hours or days, even weeks to simulate airflow in a building by using CFD on a single central processing unit (CPU) computer. Parallel computing on a multi-CPU supercomputer or computer cluster can reduce the computing time, but the cost for such high performance computing is prohibitive for many designers. Our paper introduces high performance parallel computing of the airflow simulations on a graphics processing unit (GPU). The computing time can be reduced by 10 - 30 times using the GPU. Furthermore, the cost of purchasing such a GPU is only $500, which is less than 2% of a multi-CPU supercomputer or a computer cluster for the same performance.
... In order to accelerate the CFD simulation, some researchers (Beghein et al. 2005;Crouse et al. 2002;Mazumdar and Chen 2008) used multi-processor supercomputers or computer clusters. The speed was much faster but this approach required expensive computing facilities, a space for installing the computer, and a large cooling system to cool the computer (Feng and Hsu 2004). ...
Article
Full-text available
Building design and operation often requires real-time or faster-than-real-time simulations for detailed information on air distributions. By solving the Navier-Stokes equations and transportation equations for energy and species, Fast Fluid Dynamics (FFD) model can provide detailed information as a Computational Fluid Dynamics (CFD) model. Compared to the CFD, the FFD is 50 times faster with some compromise in accuracy. But the accuracy and speed of the FFD model can be further enhanced by improving its numerical schemes. In addition, it was found that the computing time of the FFD program can be reduced up to 30 times by executing on a Graphics Processing Unit (GPU) instead of a Central Processing Unit (CPU). Furthermore, the FFD simulation can be accelerated by optimizing the GPU code and by using multiple GPUs. As a whole, it is possible to perform real-time simulation for a moderate size building with 107 grids and Δt = 0.1s using the FFD on GPUs
... This study used a fully occupied 15-row cabin section with a seat pitch of 0.86 m. The thermo-fluid conditions as shown in Table 2 along with the passenger and the seat model were similar to those used by Mazumdar and Chen (2008). This study examined:  The contaminant transport in the moving body wake  The effect of moving body speed on the contaminant transport  The influence of the moving body shape on the contaminant transport by using the full-scale CFD model of the Air China Flight 112. ...
Article
Studies of contaminant transport have been conducted using small-scale models. This investigation used validated Computational Fluid Dynamics (CFD) to examine if a small-scale water model could reveal the same contaminant transport characteristics as a full-scale airliner cabin. But due to similarity problems and the difficulty of scaling the geometry, a perfect scale up from a small water model to an actual air model was found to be impossible. The study also found that the seats and passengers tended to obstruct the lateral transport of the contaminants and confine their spread to the aisle of the cabin. The movement of a crew member or a passenger could carry a contaminant in its wake to as many rows as the crew member or passenger passed. This could be the reason why a SARS infected passenger could infect fellow passengers who were seated seven rows away. To accurately simulate the contaminant transport, the shape of the moving body should be a human-like model.
... Carefullydesigned laboratory experiments with controlled thermo-fluid conditions provide accurate and useful information. However, the airliner cabin configuration and thermo-fluid conditions can vary considerably, making experimental investigations under varied cabin circumstances time-consuming, expensive and difficult (Mazumdar and Chen, 2008). Therefore, measured data from a properly controlled laboratory experiment are usually used to test the performance of versatile and efficient numerical models, which may be used to further study the influence of variations in cabin configuration and thermo-fluid conditions. ...
Article
The effects of a moving human body on flow and contaminant transport inside an aircraft cabin were investigated. Experiments were performed in a one-tenth scale, water-based model. The flow field and contaminant transport were measured using the Particle Image Velocimetry (PIV) and Planar Laser-Induced Fluorescence (PLIF) techniques, respectively. Measurements were obtained with (ventilation case) and without (baseline case) the cabin environmental control system (ECS). The PIV measurements show strong intermittency in the instantaneous near-wake flow. A symmetric downwash flow was observed along the vertical centerline of the moving body in the baseline case. The evolution of this flow pattern is profoundly perturbed by the flow from the ECS. Furthermore, a contaminant originating from the moving body is observed to convect to higher vertical locations in the presence of ventilation. These experimental data were used to validate a Computational Fluid Dynamic (CFD) model. The CFD model can effectively capture the characteristic flow features and contaminant transport observed in the small-scale model.
Article
Airplane cabin ventilation is essential to ensure passengers' well‐being. The conventional ventilation method is mixing ventilation with a statistically steady supply, which, according to former studies, has reached its limits regarding, for example, the ventilation efficiency. However, the effect of a statistically unsteady (time‐periodic) supply on the mixing ventilation efficiency has remained largely unexplored. This research uses computational fluid dynamics (CFD) with the large eddy simulation (LES) approach to study isothermal time‐periodic mixing ventilation in a section of a single‐aisle airplane cabin model, in which the air exhaled by the passengers functions as (passive) contaminants. Two time‐periodic supply strategies are evaluated. The induced time‐periodic airflow patterns promote an efficient delivery of fresh air to the passenger zone and affect the passengers' expiratory plumes. This results in increased mean contaminant mass fluxes, causing a strong reduction of the mean contaminant concentrations in the passenger zone (up to 23%) and an increased contaminant extraction from the cabin. Mean velocities increase with up to 55% but remain within the comfortable range. It is shown that the ventilation efficiency improves; that is, the contaminant removal effectiveness and air change efficiency (in the full cabin volume) increase with up to 20% and 7%, respectively.
Article
Accurate computational fluid dynamics (CFD) simulations of the ventilation flow in airplane cabins are important for ventilation design optimisation regarding passenger health, thermal comfort and energy efficiency. The complex unsteady flow phenomena inside the cabin are challenging in numerical modelling and therefore dedicated validation of the simulation outcomes is required. The majority of airplane ventilation studies performed steady Reynolds-averaged Navier-Stokes (RANS) simulations and focused mainly on global flow field characteristics. This paper presents both steady RANS and transient simulations, including unsteady RANS and large eddy simulations (LES), of the flow driven by opposing plane wall jets in a reduced-scale isothermal water-filled generic airplane cabin. A detailed analysis of the mean velocity and turbulence characteristics (including Reynolds stresses) of the cabin flow is outlined, encompassing a thorough investigation of the fundamental flow components such as the opposing jets and the merged jet. Specific attention is devoted to LES grid sensitivity and the performance of different RANS turbulence and LES subgrid-scale (SGS) models is assessed by comparison with particle image velocimetry (PIV) measurements. It is shown that LES in general performs much better than RANS, the latter being incapable of providing accurate mean flow characteristics within the interaction zone and merged jet due to the underlying dynamic opposing jet interaction. Unsteady RANS partly covers the unsteadiness, however, turbulence levels remain systematically underpredicted and LES is required for a correct representation. Differences between the LES SGS model predictions are limited to the SGS kinetic energy budget of the total turbulent kinetic energy.
Article
Sensors in buildings are used for a wide variety of applications such as monitoring air quality, contaminants, indoor temperature, and relative humidity. These are used for accessing and ensuring indoor air quality, and also for ensuring safety in the event of chemical and biological attacks. It follows that optimal placement of sensors become important to accurately monitor contaminant levels in the indoor environment. However, contaminant transport inside the indoor environment is governed by the indoor flow conditions which are affected by various uncertainties associated with the building systems including occupancy and boundary fluxes. Therefore, it is important to account for all associated uncertainties while designing the sensor layout. The transfer operator based framework provides an effective way to identify optimal placement of sensors. Previous work has been limited to sensor placements under deterministic scenarios. In this work we extend the transfer operator based approach for optimal sensor placement while accounting for building systems uncertainties. The methodology provides a probabilistic metric to gauge coverage under uncertain conditions. We illustrate the capabilities of the framework with examples exhibiting boundary flux uncertainty.
Preprint
Full-text available
Dynamical system-based linear transfer Perron- Frobenius (P-F) operator framework is developed to address analysis and design problems in the building system. In particular, the problems of fast contaminant propagation and optimal placement of sensors in uncertain operating conditions of indoor building environment are addressed. The linear nature of transfer P-F operator is exploited to develop a computationally efficient numerical scheme based on the finite dimensional approximation of P-F operator for fast propagation of contaminants. The proposed scheme is an order of magnitude faster than existing methods that rely on simulation of an advection-diffusion partial differential equation for contami- nant transport. Furthermore, the system-theoretic notion of observability gramian is generalized to nonlinear flow fields using the transfer P-F operator. This developed notion of observability gramian for nonlinear flow field combined with the finite dimensional approximation of P-F operator is used to provide a systematic procedure for optimal placement of sensors under uncertain operating conditions. Simulation results are presented to demonstrate the applicability of the developed framework on the IEA-annex 2D benchmark problem.
Chapter
Accurate identification of plant pests is essential to maintaining a successful plant biosecurity programme. Diagnostic methods and technologies used by national regulatory programmes (NPPOs), and associated laboratories for identification, are driven by method/protocol availability, taxonomy and biology of the pest, all informed by accurate reference collections and genetic databases. The ultimate selection and implementation of specific diagnostics for any programme is influenced by the unique circumstances faced by each plant protection organization. While regulatory diagnostics are used to protect agriculture and the environment, they also must be accomplished while maintaining open agricultural trade. Much information is needed to fit the diagnostic to its intended use and avoid improper use or assay failure. The components that currently drive method development and deployment of systems for regulatory identification and diagnosis include criteria for method selection, development, and transfer to the field. Diagnostic methods that are developed using quality management guidelines and appropriate validation strategies can produce universally acceptable results for regulatory decisions. Technologies that are serological, genome based, or detect volatile signatures can supplement morphological and visual identification as well as independently provide accurate identification of regulatory pests. Each NPPO continues to evolve its utility to pest detection by advancing new technologies such as DNA barcodes, recombinant DNA produced monoclonal antibodies, and novel ways of detecting targeted nucleic acids. Use of two or more assays to fulfill regulatory requirements adds diversity for cross-checking and accountability of the results when high-consequence regulatory decisions are made.
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In 2003, Severe Acute Respiratory Syndrome (SARS) affected more than 8000 patients and caused 774 deaths in 26 countries across five continents within months after its emergence in rural China. The pandemic illustrated the dramatic role of globalization and air travel in the dissemination of an emerging infectious disease. Other cases of airborne infectious diseases transmitted in airliners in recent years include tuberculosis, influenza, measles, and mumps. Computational Fluid Dynamics (CFD) is a very attractive tool in studying the transmission of airborne contaminants in an airliner cabin as it is inexpensive and flexible in changing thermo-fluid conditions inside the cabins compared to experimental measurements. Due to many approximations used in CFD, its results should always be validated using high quality experimental data. By using the measured velocity fields obtained from a small-scale, water cabin mockup, this study found that CFD can capture the fundamental flow features although the discrepancies between the measured and computed results exist. The validated CFD model was then used to study gaseous contaminant transport inside an airliner cabin. The CFD results show that the movement of a person might have resulted in the spread of SARS viruses to the passengers seated far away from the contagious passenger in the flight from Hong Kong to Beijing in 2003.
Article
Due to the limit of computing resources, it's difficult to process numerical simulation with a full-scale cabin. The determination of reasonable row number for aircraft cabin is the basis to acquire real information of airflow. This investigation explores the reasonable row number in a section of a single-aisle aircraft cabin with a validated computational fluid dynamics(CFD)program. The simulation of reasonable row number cases includes the empty cabin and the fully-occupied cabin and the row number differs from one row, three rows, five rows, seven rows to nine rows. The RNG k-ε model for the turbulent flow is used to simulate a steady air flow in the cabin environment during cruise flight. It found that as for the empty cabin, due to the influence of complex geometry boundary, five rows are enough for simple numerical simulation and the seven-row layout can obtain good results. As the thermal plume from manikin has larger impact on airflow distribution inside the aircraft cabin compared to geometry boundary, three rows are enough for the numerical simulation of the fully-occupied cabin. With the obtained reasonable full-occupied row number, this investigation further compares the air distribution between the halfoccupied cabin and the full-occupied cabin. The results show that different from the full-occupied condition, air distribution in the half-occupied aircraft cabin appears asymmetrical and airflow deviates from aisle to the side with more people.
Article
The wake produced by a bluff body driven through a steady recirculating flow is studied experimentally in a water facility using particle image velocimetry. The bluff body has a rectangular cross section of height, H, and width, D, such that the aspect ratio, AR = H/D, is equal to 3. The motion of the bluff body is uniform and rectilinear, and corresponds to a Reynolds number based on width, Re D = 9,600. The recirculating flow is confined within a hemicylindrical enclosure and is generated by planar jets emanating from slots of width, h, such that Reh=500Re_h=500. Under these conditions, experiments are performed in a closed-loop facility that enables complete optical access to the near-wake. Velocity fields are obtained up to a distance of 13D downstream of the moving body. Data include a selection of phase-averaged velocity fields representative of the wake for a baseline case (no recirculation) and an interaction case (with recirculation). Results indicate that the transient downwash flow typically observed in wakes behind finite bodies of small aspect ratio is significantly perturbed by the recirculating flow. The wake is displaced from the ground plane and exhibits a shorter recirculation zone downstream of the body. In summary, it was found that the interaction between a bluff body wake and a recirculating flow pattern alters profoundly the dynamics of the wake, which has implications on scalar transport in the wake.
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A coupled computational fluid dynamics (CFD) and analytical model is presented for accurate and time-efficient prediction of transient airborne contaminant transmission in full-length airliner cabins. The CFD model was used at locations near the contaminant source, while the analytical model was used for the rest of the cabin. The CFD and analytical model coupling used two different methods for solving the transient contaminant flux. One method forced an outflow condition at the interface of the CFD; this analytical model is less accurate but easier to implement in commercial CFD software. The other method that iteratively solved the contaminant flux at the interface is more accurate but is computationally intensive. A procedure to analytically calculate the contaminant concentration using the transient contaminant flux condition at the interface was also developed.
Conference Paper
An integrated research and development program is being pursued by academia and industry in the United States to quantify a number of important safety and health issues within airliner cabins. This paper will present an overview of recent results as well as the current status of the airliner cabin environment research activities underway by the FAA-funded National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE). Research to be discussed includes cabin ozone levels, pesticide exposures, cabin pressure effects on health-compromised passengers and crew, cabin air quality sensing, infectious disease transmission as well as aircraft disinfection and decontamination processes including aircraft materials compatibility studies. The research results are expected to influence government rule-making actions in the future as well as provide the basis for design or operational changes by the private sector relevant to the aircraft cabin environment. © 2010 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Conference Paper
A model for predicting the airflow inside an aircraft interior is presented in this paper. The objective was to optimize the amount of air flowing inside the aircraft at the time of painting, in order to dry the paint effectively and to minimize hazardous effects on the painting crew. The hangar area was split into three regions such that three aircrafts were placed for the purpose of painting. The three regions were separated with curtains between them which acted as separators between the aircraft. A 3D model of the aircraft fuselage with its openings was developed. The fuselage has two pilot doors, two escape hatches and two rear doors on each side of the aircraft. There are two dog houses at the bottom of the aircraft as doors to cargo section of the aircraft. Air flowing over the aircraft on the exterior is forced through into the aircraft through these eight openings provided. Air is forced out through the dog houses. The analysis was carried out for seven different scenarios in which the pilot and rear doors were chosen to be closed randomly. Two major constraints to maintain a minimum velocity of 100fpm (0.51 m/sec) throughout the inside of the aircraft and 12000 cfm (5.64 m3 /sec) of air at each exit (dog houses). A minimum of 12000 cfm (5.64 m3 /sec) at each exit was available in all scenarios, but the minimum requirement of 100 fpm (0.51 m/sec) was satisfactorily achieved only in which all the doors were open.
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Simulated magnetic contamination of plants during early ontogenetic stages was studied in arranged laboratory conditions using magnetic nanoparticles based on compound metal oxides. Aqueous suspensions of magnetic colloidal nanoparticles of Fe3O4, CoFe2O4, and ZnFe2O4, were administrated to freshly germinated sunflower seeds in the same array of dilutions (v/v): 20-40-60-80-100 mu l/l, the results of their genetic impact in the root tip cells being qualitatively and quantitatively analyzed. Cytogenetic tests carried out by optical microscopy means provided data on the types of abnormal cell divisions as well as on the mitosis rate and total percentage of chromosomal aberrations. Considerable diminished mitosis rate was evidenced in all situations, while remarkably enhanced number of chromosomal aberrations was also evidenced for all three cases with higher nanotoxicity revealed in the case of ZnFe2O4 and CoFe2O4. Chromosome fragments, interchromatidian bridges and micronuclei appeared in most analyzed samples with no noticeable difference for one type of magnetic nanoparticles or other.
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The spread of particles or contaminants in aircraft cabins is of interest due to the large number of passengers and their close proximity to each other. This close proximity causes concern about the spread of disease and contaminants among passengers. To understand the aircraft cabin environment and the dispersion of fine particles, an experimental study was conducted in an 11-row wide-body aircraft cabin mockup. The experiment focused on the longitudinal dispersion of particles throughout the cabin. The data show the regions close to the source experience higher levels of exposure and higher levels of variation, while locations farther from the source show lower exposure levels and less variation. The variations close to the source likely stem from the interaction of the quick injection burst of particles with chaotic airflow. Particles release in the second row were detected at all locations in the cabin mockup, but there was roughly a 37% decrease in concentration with each successive row in the longitudinal direction from the release location.
Article
Accurate prediction of particle deposition in airliner cabins is important for estimating the exposure risk of passengers to infectious diseases. This study developed a Detached Eddy Simulation (DES) model with a modified Lagrangian method. The computer model was validated with experimental data for particle deposition in a cavity with natural convection and with air velocity, air temperature, and particle concentration data from a four-row, twin-aisle cabin mockup. The validation showed that the model performed well for the two cases. Then the model was further used to study particle deposition in the cabin mockup with seven sizes of particles. The particles were assumed to be released from an index passenger due to breathing or talking at zero velocity and due to coughing at a suitable jet velocity. This study can provide quantitative particle deposition distributions for different surfaces and particles removed by cabin ventilation.
Conference Paper
The spread of disease via commercial airliner travel is a significant and realistic threat. To shed some light on the feasibility of detecting airborne pathogens a sensor integration study has been conducted in this work, in addition to computational investigations of the contaminant transport in an aircraft cabin. Our sensor study took into consideration sensor sensitivity as well as the size, weight and power of best available commercial off-the-shelf devices. Computational fluid dynamic simulations were made to investigate extreme coughing and sneezing scenarios. The principle finding was that contaminant concentrations in aircraft are below the sensitivity thresholds of current state of the art devices. Therefore, this study proposes the development of a novel bio-detector to achieve single particle detection limits for pathogen sensing in airline cabins.
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Physicians are often asked to provide assistance when symptoms develop in a passenger during a commercial flight. This Review Article identifies the most common problems that develop during air travel. The authors recommend ways to respond to such events and describe the resources that are available to physicians and flight crews while the aircraft is still airborne.
Article
A three-dimensional thermal airflow analysis computer program for an airplane cabin air distribution system has been developed in order to facilitate design improvements. This program is based on an incompressible Navier-Stokes code in generalized three-dimensional coordinates (INS3D). The original program was modified to add capabilities of computing thermal (buoyancy) effects and contaminant (carbon dioxide) dispersion and treating the influence of internal obstructions such as passenger seats. This paper presents a description of modifications of the program, the technique used in modeling an airplane cabin, a description of the configuration and conditions analyzed and a description of verification tests, and a discussion of the prediction accuracy, usefulness, and problems encountered as a result of comparing analysis and test data.
Article
Terrorist attack in buildings by chemical and biological agents (CBAs) is a reality in our lives. This study applies computational fluid dynamics (CFD) to predict CBA dispersion in an office building in order to find the best locations for CBA sensors and to develop effective ventilation systems to protect building occupants in case of indoor CBA releases. It is found that the CFD is a useful tool for such an application, while some challenges remain.
Article
Abstract Current guidelines for green buildings are cursory and inadequate for specifying materials and designing ventilation systems to ensure a healthful indoor environment, i.e. a "healthy building," by design. Public perception, cultural preferences, litigation trends, current codes and regulations, and rapid introduction of new building materials and commercial products, as well as the prevailing design-build practices, pose challenges to systems integration in the design, construction and operation phases of modern buildings. We are on the verge of a paradigm shift in ventilation design thinking. In the past, thermal properties of air within a zone determined heating, ventilating, and air-conditioning specifications. In the future, occupant-specific and highly responsive systems will become the norm. Natural ventilation, displacement ventilation, and microzoning with subfloor plenums, along with the use of point-of-source heat control and point-of-use sensors, will evolve to create a "smart," responsive ventilation-building dynamic system. Advanced ventilation design tools such as the modeling of computational fluid dynamics (CFD) will be used routinely. CFD will be integrated into air quality and risk assessment models.
Article
In this article, Jive k-ε, two-equation models are studied: the standard k-ε model, a low-Reynolds-number k-ε model, a two-layer k-ε model, a two-scale k-ε model, and a renormalization group (RNG) k-ε model. They are evaluated for their performance in predicting natural convection, forced convection, and mixed convection in rooms, as well as an impinging jet flow. Corresponding experimental data from the literature are used for validation. It is found that the prediction of the mean velocity is more accurate than that of the turbulent velocity. These models are neither able to predict anisotropic turbulence correctly nor to pick up the secondary recirculation of indoor air flow; otherwise the performance of the standard k-ε model is good. The RNG k-ε model is slightly better than the standard k-ε model and is therefore recommended for simulations of indoor airflow. The performance of the other models is not stable.
Article
A comparison of computational fluid dynamics (CFD) predictions and experimental data for the airflow in a generic cabin model is presented in this paper. The CFD predictions were generated using the large eddy simulation (LES) model, while the particle image velocimetry (PIV) technique was used to obtain the experimental data. A brief summary of the test setup and the experimental data are described herein. The main focus of this study is to analyze the temporal variation of the experimental data. The time series of the PIV measured velocity components with sampling frequencies of 0.1 and 5 Hz were compared with the CFD predictions, sampling at 20 Hz. Energy spectral analysis, through fast Fourier transformation (FFT) on the PIV data and their CFD counterparts, was performed and is presented in this study.By using direct comparisons of the velocity data, good agreement on the range of the velocity components was obtained at all monitoring locations, hence validating the LES predictions. A similar conclusion can be reached from the results of the energy spectral analysis. The energy-spectrum function calculated from the LES predicted velocity magnitudes has excellent correlation with the Kolmogorov spectrum law in the universal equilibrium range. For the smaller wave numbers, the PIV data taken at 0.1 Hz clearly reveal the characteristic motion of the largest eddy in the flow domain, and it correlates very well with the CFD predictions.
Article
The application of numerical methods to the analysis of heat-transfer problems is examined and illustrated in a textbook for advanced students of engineering and applied mathematics. The basic methods are introduced, including finite-difference, finite-element, variational, global-function, central-integration, least-squares, collocation, higher-order-element, method-of-moments, perturbation, and nonlinear two-point boundary-value techniques, and their numerical stability, consistency, convergence, accuracy, and efficiency are evaluated. The fundamental modes of heat transfer (conduction, convection, and radiation) are then analyzed, with an emphasis on laminar forced convection, and the treatment of additional phenomena such as free and mixed convection, turbulence, and combustion is explained. An analysis of the error bounds of the various methods and a detailed comparison of the finite-difference and finite-element methods are included.
Article
Air distribution systems in commercial aircraft cabins are important for providing a healthy and comfortable environment for passengers and crew. The mixing air distribution systems used in existing aircraft cabins create a uniform air temperature distribution and dilute contaminants in the cabins. The mixing air distribution systems could spread infectious airborne diseases. To improve the air distribution system design for aircraft cabins, this investigation proposed an under-floor displacement air distribution system and a personalized air distribution system. This study first validated a computational fluid dynamics (CFD) program with the experimental data of airflow, air temperature, and tracer-gas concentration from an environmental chamber. Then the validated CFD program was used to calculate the distributions of the air velocity, air temperature, and CO2 concentration in a section of Boeing 767 aircraft cabin with the mixing, under-floor displacement, and personalized air distribution systems, respectively. By comparing the air and contaminant distributions in the cabin, this study concluded that the personalized air distribution system provided the best air quality without draft risk.
Article
In April 1994, a passenger with infectious multi-drug resistant tuberculosis traveled on commercial-airline flights from Honolulu to Chicago and from Chicago to Baltimore and returned one month later. We sought to determine whether she had infected any of her contacts on this extensive trip. Passengers and crew were identified from airline records and were notified of their exposure, asked to complete a questionnaire, and screened by tuberculin skin tests. Of the 925 people on the airplanes, 802 (86.7 percent) responded. All 11 contacts with positive tuberculin skin tests who were on the April flights and 2 of 3 contacts with positive tests who were on the Baltimore-to-Chicago flight in May had other risk factors for tuberculosis. More contacts on the final, 8.75-hour flight from Chicago to Honolulu had positive skin tests than those on the other three flights (6 percent, as compared with 2.3, 3.8, and 2.8 percent). Of 15 contacts with positive tests on the May flight from Chicago to Honolulu, 6 (4 with skin-test conversion) had no other risk factors; all 6 had sat in the same section of the plane as the index patient (P=0.001). Passengers seated within two rows of the index patient were more likely to have positive tuberculin skin tests than those in the rest of the section (4 of 13, or 30.8 percent, vs. 2 of 55, or 3.6 percent; rate ratio, 8.5; 95 percent confidence interval, 1.7 to 41.3; P=0.01). The transmission of Mycobacterium tuberculosis that we describe aboard a commercial aircraft involved a highly infectious passenger, a long flight, and close proximity of contacts to the index patient.
Article
The severe acute respiratory syndrome (SARS) spread rapidly around the world, largely because persons infected with the SARS-associated coronavirus (SARS-CoV) traveled on aircraft to distant cities. Although many infected persons traveled on commercial aircraft, the risk, if any, of in-flight transmission is unknown. We attempted to interview passengers and crew members at least 10 days after they had taken one of three flights that transported a patient or patients with SARS. All index patients met the criteria of the World Health Organization for a probable case of SARS, and index or secondary cases were confirmed to be positive for SARS-CoV on reverse-transcriptase polymerase chain reaction or serologic testing. After one flight carrying a symptomatic person and 119 other persons, laboratory-confirmed SARS developed in 16 persons, 2 others were given diagnoses of probable SARS, and 4 were reported to have SARS but could not be interviewed. Among the 22 persons with illness, the mean time from the flight to the onset of symptoms was four days (range, two to eight), and there were no recognized exposures to patients with SARS before or after the flight. Illness in passengers was related to the physical proximity to the index patient, with illness reported in 8 of the 23 persons who were seated in the three rows in front of the index patient, as compared with 10 of the 88 persons who were seated elsewhere (relative risk, 3.1; 95 percent confidence interval, 1.4 to 6.9). In contrast, another flight carrying four symptomatic persons resulted in transmission to at most one other person, and no illness was documented in passengers on the flight that carried a person who had presymptomatic SARS. Transmission of SARS may occur on an aircraft when infected persons fly during the symptomatic phase of illness. Measures to reduce the risk of transmission are warranted.
Article
Unlabelled: This paper reports on an investigation of the adequacy of computational fluid dynamics (CFD), using a standard Reynolds Averaged Navier-Stokes (RANS) model, for predicting dispersion of neutrally buoyant gas in a large indoor space. We used CFD to predict pollutant (dye) concentration distribution in a water-filled scale model of an atrium with a continuous pollutant source in the absence of furniture and occupants. Predictions from the RANS formulation are comparable with an ensemble average of independent identical experiments. Model results were compared with pollutant concentration data in a horizontal plane from experiments in a scale model atrium. Predictions were made for steady-state (fully developed) and transient (developing) pollutant concentrations. Agreement between CFD predictions and ensemble averaged experimental measurements is quantified using the ratios of CFD-predicted and experimentally measured dye concentration at a large number of points in the measurement plane. Agreement is considered good if these ratios fall between 0.5 and 2.0 at all points in the plane. The standard k-epsilon two-equation turbulence model obtains this level of agreement and predicts pollutant arrival time to the measurement plane within a few seconds. These results suggest that this modeling approach is adequate for predicting isothermal pollutant transport in a large room with simple geometry. Practical implications: CFD modeling of pollutant transport is becoming increasingly common but high quality comparisons between CFD and experiment remain rare. Our results provide such a comparison. We demonstrate that the standard k-epsilon model provides good predictions for both transient and fully developed pollutant concentrations for an isothermal large space where furnishings are unimportant. This model is less computationally intensive than a large eddy simulation or low Reynolds number k-epsilon model.
Article
Because of the increasing ease and affordability of air travel and mobility of people, airborne, food-borne, vector-borne, and zoonotic infectious diseases transmitted during commercial air travel are an important public health issue. Heightened fear of bioterrorism agents has caused health officials to re-examine the potential of these agents to be spread by air travel. The severe acute respiratory syndrome outbreak of 2002 showed how air travel can have an important role in the rapid spread of newly emerging infections and could potentially even start pandemics. In addition to the flight crew, public health officials and health care professionals have an important role in the management of infectious diseases transmitted on airlines and should be familiar with guidelines provided by local and international authorities.
Article
Unlabelled: This paper presents the experimental and numerical modeling of contaminant dispersion in a full-scale environmental chamber with different room air distribution systems. For the experimental modeling, an area source with uniform emissions of a hypothetical contaminant (SF6) from the entire floor surface is designed and constructed. Two different types of ventilation are studied: displacement and mixing ventilation. A computer model for predicting the contaminant dispersion in indoor spaces was validated with experimental data. The validated model is used to study the effects of airflow and the area-source location on contaminant dispersion. Results show that the global airflow pattern has a strong impact on the distribution of the contaminants. In general, the personal exposure could be estimated by analyzing the relative source positions in the airflow pattern. Accordingly, the location of an exhaust diffuser may not greatly affect the airflow pattern, but can significantly affect the exposure level in the room. Practical implications: When designing ventilation in addition to bringing fresh air to occupants, it is important to consider the removal of contaminants released in the off-gassing of building materials. Typical indoor off-gassing examples are emissions of volatile organic compounds from building enclosure surfaces such as flooring and painted walls. In this study, we conducted experimental and numerical modeling of different area sources in a mock-up office setup, with displacement or mixing ventilation. Displacement ventilation was as successful as mixing ventilation in removing the contaminant source from the floor area. Actually, the most important consideration in the removal of these contaminants is the relative position of the area source to the main airflow pattern and the occupied zone.
Article
Estimating exposure to contaminants emitted into workroom air is essential for worker protection. Although contaminant concentrations are often not spatially uniform within workrooms, many methods for estimating exposure do not adequately account for this variability. Here the impact of temperature differences within a room on spatial contaminant distribution was studied. Tracer gas (99.5% propylene) concentrations were monitored automatically at 144 sampling points with a photoionization detector. One wall was chosen to represent a building's external wall and was heated or cooled to simulate summer or winter conditions. Experiments were preformed at two flow rates (5.5 and 3.3 m(3) min(-1)) and six thermal conditions (isothermal, three summer conditions and two winter conditions). For 5.5 m(3) min(-1) and all thermal conditions, the coefficient of variation (CV) ranged from 0.34 to 0.45 and the normalized average concentrations were similar. For 3.3 m(3) min(-1), winter conditions produced greater spatial variability of concentration (CV = 0.72 and 1.10) than isothermal or summer conditions (CV range = 0.29-0.34). Tests simulating winter conditions suggest that the resulting stable temperature structure inhibited the dilution of the tracer and enhanced its segregation in the lower portion of the room, especially for the lower flow rate (3.3 m(3) min(-1)). Therefore, not explicitly addressing thermal effect in exposure modeling may impact the estimated accuracy and precision when used for rooms that are non-isothermal and not well mixed. These findings also have implications for air monitoring. Dispersion patterns for different thermal conditions were found to be substantially different, even when the mean concentrations were nearly the same. Thus, monitoring data from a single season should not be taken as representative of the entire year, when summer and winter conditions create temperature gradients in a room.
Article
Unlabelled: In case contaminants are found in enclosed environments such as aircraft cabins or buildings, it is useful to find the contaminant sources. One method to locate contaminant sources is by inverse computational fluid dynamics (CFD) modeling. As the inverse CFD modeling is ill posed, this paper has proposed to solve a quasi-reversibility (QR) equation for contaminant transport. The equation improves the numerical stability by replacing the second-order diffusion term with a fourth-order stabilization term in the governing equation of contaminant transport. In addition, a numerical scheme for solving the QR equation in unstructured meshes has been developed. This paper demonstrates how to use the inverse CFD model with the QR equation and numerical scheme to identify gaseous contaminant sources in a two-dimensional aircraft cabin and in a three-dimensional office. The inverse CFD model could identify the contaminant source locations but not very accurate contaminant source strength because of the dispersive property of the QR equation. The results also show that this method works better for convection dominant flows than the flows that convection is not so important. Practical implications: This paper presents a methodology that can be used to find contaminant source locations and strengths in enclosed environments with the data of airflow and contaminants measured by sensors. The method can be a very useful tool to find where, what, and how contamination has happened. The results can be used to develop appropriate measures to protect occupants in the enclosed environments from infectious diseases or terrorist releases of chemical/biological warfare agents as well as to decontaminate the environments.
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