Novel air distribution systems for commercial aircraft cabins

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.     

Experimental parametric study of forced and mixed convection in a passenger aircraft cabin mock-up

Forced and mixed convection has been investigated experimentally in a full scale passenger aircraft cabin mock-up. The mock-up represents a generic cabin section of the A380 upper deck. Large scale particle image velocimetry (PIV) and temperature field measurements were conducted in a cross sectional plane of the cabin mock-up. The flow fields for two different air inlet configurations were measured and analysed under isothermal and cooling conditions. Furthermore the flow rates at the different air inlet positions were varied while keeping the air exchange rate constant. Our extensive experimental parametric study demonstrates that the flow field in aircraft cabins is affected by various fluid mechanical phenomena. Interaction between the supplied air jets, negative buoyancy forces acting on these air jets and interaction of thermal plumes with the supplied air jets, all influence the flow field inside the cabin. The impact of these effects differs considerably depending on the ventilation configuration and relative mass flow settings at the supply inlets.     

Numerical modeling of particle deposition in the environmental control systems of commercial airliners on ground

The environmental control system (ECS) of a commercial airplane supplies air to the cabin in order to maintain a safe, comfortable, and healthy environment for passengers and crew members. Because about half of the air supplied to the cabin is outside air, atmosphere particles could deposit in the ECS before entering the cabin. This investigation developed a model to calculate the particle deposition rates in the ECS for different particle sizes on the basis of a set of empirical equations from the literature. The model was used to predict particle deposition in five types of commercial airplanes (a regional jet, Boeing 737-800, Airbus 319, Airbus 320, and MD-82). The predicted results were compared with data measured in-flight or during operation on the ground and agreed well with the measured data. Both the simulated and measured results showed that almost all the large particles (d _p ≥ 5.0 μm) and 75% of small particles (d _p = 0.3–5.0 μm) were deposited in the ECS. Most of the particle deposition occurred near the entrance to the ECS where the geometry was the most complex.     

Novel personalized and humidified air supply for airliner passengers

The micro-environment control in an airliner cabin presented here consists in supplying each of the passengers with her/his own supply of fresh, humidified air in order to prevent possible airborne health problems and to provide local compensation for the humidity deficit. Unlike the environment control systems widely used in commercial aircraft, each of the seats in the cabin will be supplied individually with a separate airflow, which is also separately exhausted. This arrangement forms a personalized microclimate in the seat area. Essentially, focusing a personal air supply into the breathing area of the passenger works on the principle of individual seat ventilation, with the air supply and exhaust nozzles built into the back of the seat ahead. The system design, originally based on Computational Fluid Dynamics (CFD) models, has been verified by means of laboratory experiments. The results presented here have been achieved within the framework of FP6 EU Project AST5-CT-2006-030958, under the acronym SEAT (www.seat-project.org).     

Mitigation of cross-contamination in an aircraft cabin via localized exhaust

Most aircraft cabin ventilation designs currently use a 50% mix of fresh and recirculated, filtered air and supply approximately 8–10 l/s per person. In order to make the most efficient use of the air supply at hand, the 50% of cabin air that is exhausted from the aircraft should remove with it as much contaminant from within the cabin as possible. This will thereby reduce cross-contamination among passengers and improve overall air quality. This study examines the use of localized suction orifices near and around the source occupant to unobtrusively ingest the individual’s thermal plume and exhaust it from the aircraft cabin before contaminants entrained in the plume can significantly mix with the bulk airflow. Through the use of Computational Fluid Dynamics (CFD), various suction seat designs have been tested for their contaminant removal effectiveness and subsequent cross-contamination reduction. CFD results indicate significant improvements over conventional mixing air ventilation systems with a 40–50% decrease in passenger exposure predicted in a conventional coach-class seating arrangement.     

Experimental studies of thermal environment and contaminant transport in a commercial aircraft cabin with gaspers on

Gaspers installed in commercial airliner cabins are used to improve passengers' thermal comfort. To understand the impact of gasper airflow on the air quality in a cabin, this investigation measured the distributions of air velocity, air temperature, and gaseous contaminant concentration in five rows of the economy‐class section of an MD‐82 commercial aircraft. The gaseous contaminant was simulated using SF₆ as a tracer gas with the source located at the mouth of a seated manikin close to the aisle. Two‐fifths of the gaspers next to the aisle were turned on in the cabin, and each of them supplied air at a flow rate of 0.66 l/s. The airflow rate in the economy‐class cabin was controlled at 10 l/s per passenger. Data obtained in a previous study of the cabin with all gaspers turned off were used for comparison. The results show that the jets from the gaspers had a substantial impact on the air velocity and contaminant transport in the cabin. The air velocity in the cabin was higher, and the air temperature slightly more uniform, when the gaspers were on than when they were off, but turning on the gaspers may not have improved the air quality.     

Advantages for passengers and cabin crew of operating a gas-phase adsorption air purifier in 11-h simulated flights

Experiments were carried out in a three-row, 21-seat section of a simulated aircraft cabin installed in a climate chamber to evaluate the extent to which passengers' perception of cabin air quality is affected by the operation of a gas-phase adsorption (GPA) purification unit. A total of 68 subjects, divided into four groups of 17 subjects took part in simulated 11-h flights. Each group experienced four conditions in balanced order, defined by two outside air supply rates (2.4 and 3.3 l/s per person), with and without the GPA purification unit installed in the recirculated air system, a total of 2992 subject-hours of exposure. During each flight the subjects completed questionnaires five times to provide subjective assessments of air quality, cabin environment, intensity of symptoms, and thermal comfort. Additionally, the subjects' visual acuity, finger temperature, skin dryness, and nasal peak flow were measured three times during each flight. Analysis of the subjective assessments showed that operating a GPA unit in the recirculated air provided consistent advantages with no apparent disadvantages. PRACTICAL IMPLICATIONS: Operating a gas-phase adsorption (GPA) air purifier unit in the recirculated air in a simulated airplane cabin provided a clear and consistent advantage for passengers and crew that became increasingly apparent at longer flight times. This finding indicates that the expense of undertaking duly blinded field trials on revenue flights would be justified.     

敦煌莫高窟热环境模拟研究

通过FLUENT软件模拟对比研究乔木的遮阴作用对莫高窟热环境的影响。结论如下:三维乔木阴影区的空气温度较低,背风区域出现高温;三维乔木的遮阴作用仅对局地热环境产生影响,而对窟区整体的热环境及热岛强度影响微弱;通过调整窟区绿化的种植密度,能够改善甚至消除窟区背风区域的高热环境。     

Passenger evaluation of the optimum balance between fresh air supply and humidity from 7-h exposures in a simulated aircraft cabin

A 21-seat section of an aircraft cabin with realistic pollution sources was built inside a climate chamber capable of providing fresh outside air at very low humidity. Maintaining a constant 200 l/s rate of total air supply, i.e. recirculated and make-up air, to the cabin, experiments simulating 7-h transatlantic flights were carried out at four rates of fresh outside air supply--1.4, 3.3, 4.7, and 9.4 l/s per person (3, 7, 10, and 20 cfm/person)--resulting in humidity levels, ranging from 7% to 28% relative humidity (RH). Four groups of 16-18 subjects acted as passengers and crew and were each exposed to the four simulated flight conditions. During each flight the subjects completed questionnaires three times to provide subjective ratings of air quality and of symptoms commonly experienced during flight. Physiological tests of eye, nose, and skin function were administered twice. Analysis of the subjective assessments showed that increasing RH in the aircraft cabin to 28% RH by reducing outside flow to 1.4 l/s per person did not reduce the intensity of the symptoms that are typical of the aircraft cabin environment. On the contrary, it intensified complaints of headache, dizziness, and claustrophobia, due to the increased level of contaminants. PRACTICAL IMPLICATIONS: The investigation shows that increasing aircraft cabin humidity by decreasing the ventilation flow rate of fresh outside air would not decrease reports of discomfort made by cabin occupants.     

医用方舱舱室温度环境数值仿真研究

建立了舱室温度环境三维空气湍流流动与传热的数学模型，运用有限元方法，在空调冷射流作用下，对机动医疗系统中检验方舱舱内空气温度场、速度场进行了数值仿真，研究了舱内温度场的瞬态分布状态及变化规律，井通过试验研究，验证了计算方法的准确性。     

变风量空调系统温度模糊PID控制

将模糊PID控制应用于变风量空调系统中,任务是将送风温度和空调房间内的温度（回风温度）控制在各自的设定目标值附近。分别设计了变风量空调系统的送风温度模糊PID控制系统和室内温度（视为回风温度）模糊PID控制系统,通过调节冷冻水阀门的开度来控制送风温度,通过调节变频风机的转速来控制室内温度。应用所设计的模糊PID控制器对送风温度和空调房间的温度（即回风温度）进行了实时在线控制,控制结果表明模糊PID控制器设计合理,控制效果良好。     

An under-aisle air distribution system facilitating humidification of commercial aircraft cabins

Air environment in aircraft cabins has long been criticized especially for the dryness of the air within. Low moisture content in cabins is known to be responsible for headache, tiredness and many other non-specific symptoms. In addition, current widely used air distribution systems on airplanes dilute internally generated pollutants by promoting air mixing and thus impose risks of infectious airborne disease transmission. To boost air humidity level while simultaneously restricting air mixing, this investigation uses a validated computational fluid dynamics (CFD) program to design a new under-aisle air distribution system for wide-body aircraft cabins. The new system supplies fully outside, dry air at low momentum through a narrow channel passage along both side cabin walls to middle height of the cabin just beneath the stowage bins, while simultaneously humidified air is supplied through both perforated under aisles. By comparing with the current mixing air distribution system in terms of distribution of relative humidity, CO₂ concentration, velocity, temperature and draught risk, the new system is found being able to improve the relative humidity from the existent 10% to the new level of 20% and lessen the inhaled CO₂ concentration by 30%, without causing moisture condensation on cabin interior and inducing draught risks for passengers. The water consumption rate in air humidification is only around 0.05 kg/h per person, which should be affordable by airliners.     

Cabin air quality: indoor pollutants and climate during intercontinental flights with and without tobacco smoking

The aim was to determine cabin air quality and in-flight exposure for cabin attendants of specific pollutants during intercontinental flights. Measurements of air humidity, temperature, carbon dioxide (CO2), respirable particles, ozone (O3), nitrogen dioxide (NO2) and formaldehyde were performed during 26 intercontinental flights with Boeing 767-300 with and without tobacco smoking onboard. The mean temperature in cabin was 22.2 degrees C (range 17.4-26.8 degrees C), and mean relative air humidity was 6% (range 1-27%). The CO2 concentration during cruises was below the recommended limit of 1000 ppm during 96% of measured time. Mean indoor concentration of NO2 and O3, were 14.1 and 19.2 micrograms/m3, with maximum values of 37 and 66 micrograms/m3, respectively. The concentration of formaldehyde was below the detection limit (< 5 micrograms/m3), in most samples (77%), and the maximum value was 15 micrograms/m3. The mean concentration of respirable particles in the rear part of the aircraft (AFT galley area) was much higher (49 micrograms/m3) during smoking as compared with non-smoking conditions (3 micrograms/m3) (P < 0.001), with maximum values of 253 and 7 micrograms/m3. In conclusion, air humidity is very low on intercontinental flights, and the large variation of temperature shows a need for better temperature control. Tobacco smoking onboard leads to a significant pollution of respirable particles, particularly in the rear part of the cabin. The result supports the view that despite the high air exchange rate and efficient air filtration, smoking in commercial aircraft leads to a significant pollution and should be prohibited.     

Airflow modelling in a computer room

This study concerns the numerical simulation of airflow and the prediction of comfort properties in a visualisation room of a research centre. Because simulation accuracy depends on the modelling level, special care has been given to fine details. Particular interest has been concentrated on the four-way ceiling air supply diffuser, on the furniture and on the thermal conditions given on computers and on mannequins.

The geometric model was created using the parametric features of the pre-processor Gambit, in combination with elements created with the Rhinoceros NURBS modelling tool.

Mass, momentum, energy, turbulence, species and radiation conservation equations were solved using Fluent commercial flow solver. Computed airflow and heat transfer parameters were used for numerical prediction of indoor air quality quantities based on ISO 7730. Basic parameters included air temperature, relative humidity and air velocity. These were combined with clothing insulation and metabolic activity measures to obtain standard IAQ indices such as the mean age of air, the predicted mean vote and the predicted percentage of dissatisfied room occupants.

Post-processing was carried out with standard Fluent elements and also using Vu, a multi-platform tool which also allows data to be displayed in the Cave immersive environment.     

载人航天空间站舱内通风对流换热数值研究进展

CFD模拟是研究载人航天器舱内环境控制和地面模型试验验证的有效方法,介绍了国内外载人航天器舱内通风对流换热数值模拟的研究进展,目前的相关研究涉及舱内不同通风方式的数值模拟、通风参数的优化设计仿真、人体散热对通风环境的影响分析、舱内壁面温度分布和结露控制、微重力下通风换热问题的地面模型试验及其数值模拟验证、传热传质等诸多方面。指出数值模拟模型、舱内通风空调环境评定、通风空调系统整体优化、舱内环境数字仿真演示系统等是载人航天器舱内环境数值模拟领域值得进一步研究的问题。     

Passenger thermal comfort and behavior: a field investigation in commercial aircraft cabins

Passengers' behavioral adjustments warrant greater attention in thermal comfort research in aircraft cabins. Thus, a field investigation on 10 commercial aircrafts was conducted. Environment measurements were made and a questionnaire survey was performed. In the questionnaire, passengers were asked to evaluate their thermal comfort and record their adjustments regarding the usage of blankets and ventilation nozzles. The results indicate that behavioral adjustments in the cabin and the use of blankets or nozzle adjustments were employed by 2/3 of the passengers. However, the thermal comfort evaluations by these passengers were not as good as the evaluations by passengers who did not perform any adjustments. Possible causes such as differences in metabolic rate, clothing insulation and radiation asymmetry are discussed. The individual difference seems to be the most probable contributor, suggesting possibly that passengers who made adjustments had a narrower acceptance threshold or a higher expectancy regarding the cabin environment. Local thermal comfort was closely related to the adjustments and significantly influenced overall thermal comfort. Frequent flying was associated with lower ratings for the cabin environment.     

Experimental study of ventilation effectiveness and air velocity distribution in an aircraft cabin mockup

Ventilation effectiveness in aircraft cabins is a critical factor for minimizing the cross-contamination of airborne pathogens exhaled by the passengers. In this study, a full-scale section of a Boeing 767 aircraft cabin containing thirty five mannequins was used for evaluating the ventilation effectiveness and characterizing the air distribution. Each mannequin was attached with a body heater and an outlet of carbon dioxide to simulate breathing. A set of experiment trials was conducted to measure the local mean age of air and the ventilation effectiveness factor (VEF) at the breathing level of the passengers. Carbon dioxide was used as the trace gas to determine the local mean age of air and the VEF. The air velocity profiles measured using a volumetric particle tracking velocimetry (VPTV) system was used to generate the airflow patterns and investigate the underlying mechanism affecting the local mean age of air and the VEF. In addition, measurements were conducted at different air supply rates to examine its effect on the ventilation performance.     

Cabin air quality on non-smoking commercial flights: A review of published data on airborne pollutants

We reviewed 47 documents published 1967–2019 that reported measurements of volatile organic compounds (VOCs) on commercial aircraft. We compared the measurements with the air quality standards and guidelines for aircraft cabins and in some cases buildings. Average levels of VOCs for which limits exist were lower than the permissible levels except for benzene with average concentration at 5.9 ± 5.5 μg/m³. Toluene, benzene, ethylbenzene, formaldehyde, acetaldehyde, limonene, nonanal, hexanal, decanal, octanal, acetic acid, acetone, ethanol, butanal, acrolein, isoprene and menthol were the most frequently measured compounds. The concentrations of semi-volatile organic compounds (SVOCs) and other contaminants did not exceed standards and guidelines in buildings except for the average NO₂ concentration at 12 ppb. Although the focus was on VOCs, we also retrieved the data on other parameters characterizing cabin environment. Ozone concentration averaged 38 ppb below the upper limit recommended for aircraft. The outdoor air supply rate ranged from 1.7 to 39.5 L/s per person and averaged 6.0 ± 0.8 L/s/p (median 5.8 L/s/p), higher than the minimum level recommended for commercial aircraft. Carbon dioxide concentration averaged 1315 ± 232 ppm, lower than what is permitted in aircraft and close to what is permitted in buildings. Measured temperatures averaged 23.5 ± 0.8°C and were generally within the ranges recommended for avoiding thermal discomfort. Relative humidity averaged 16% ± 5%, lower than what is recommended in buildings.     

Predicting airflow distribution and contaminant transport in aircraft cabins with a simplified gasper model

This study investigated the air distribution and contaminant transport in aircraft cabins with gaspers by using computational fluid dynamics (CFD). If the detailed gasper geometry were used in the CFD simulations, the grid number would be unacceptably high. To reduce the grid number, this investigation proposed a method for simplifying the gasper geometry. The method was then validated by two sets of experimental data obtained from a cabin mockup and a real aircraft cabin. It was found that for the cabin mockup, the CFD simulation with the simplified gasper model reduced the grid number from 1.58 to 0.3 million and the computing cost from 2 days to 1 hour without compromising the accuracy. In the five-row economy-class cabin of the MD-82 airplane, the CFD simulation with the simplified gasper model was acceptable in predicting the distribution of air velocity, air temperature, and contaminant concentration.     

载人航天器舱内通风空调特性和数值模拟

由于载人航天器这一密闭狭小空间及其微重力这一特殊环境,舱内通风空调问题和热舒适环境与地面的HVAC问题不同,微重力效应特别是自然对流大为减弱影响着通风换热效果。本文首先分析了舱内通风空调问题的特殊性,通过无量纲分析和计算微重力的流体力学效应,然后利用FLUENT软件对两种集中通风方式进行数值模拟。模拟结果表明：微重力下几乎不存在“冷风下坠”或者“热羽”现象;集中斜进风在一定的进风角度和Re数下出现分岔解现象;与常重力相同通风条件下,微重力下自然对流的减弱使得舱内温度降低,换热减少,因此满足常重力热舒适要求的通风条件不一定满足微重力下热舒适性的要求。