Operation of gaspers for reducing airborne disease transmission in commercial airliners with personalized displacement ventilation

Abstract

By 2024, the number of air passengers had reached nearly 5 billion, which is approximately 2.5 times the level observed in 2004. As air travel gets increasingly popular, the flying public is paying more attention to the cabin environment. The air distribution system plays a critical role in creating a comfortable and healthy cabin environment. Personalized displacement ventilation systems have been developed to control contaminant transmission more effectively compared to the prevalent mixing ventilation systems and conventional displacement ventilation systems. Additionally, overhead gaspers are also available in most commercial airliners for individual ventilation and thermal regulation. However, the impact of gaspers on airborne disease transmission remains unclear. Furthermore, practical instructions for passengers on the control of airborne disease transmission in cabins are still not available. Therefore, this study aims to investigate the operation of gaspers for reducing airborne disease transmission in commercial airliners with personalized displacement ventilation system. This study first conducted experimental measurements in a simplified cabin mock-up to validate the computational fluid dynamics (CFD) method. A full-scale mockup of a three-row, single-aisle aircraft cabin with personalized displacement ventilation system was built. A gasper was mounted between the source passenger and the receptor passenger on the ceiling. The distributions of air velocity and contaminant concentration were measured on a plane located 0.05 m in front of the mouth of the second-row passengers. For each measurement point, the sampling duration was 8 minutes. Then, the measured data was used to evaluate the performance of CFD method for calculating air distribution and airborne disease transmission with the RANS SST k−ω model and the Eulerian method. The results showed that the complex interaction of the main flow, gasper-induced jet flow, and thermal plume can be accurately predicted by the CFD model. The overall normalized root mean square errors (NRMSE) of the measurement points was 0.24. Additionally, the CFD method can reliably predict the spatial distribution of contaminants. The above validated CFD method was then used to systematically investigate the impact of source and receptor passengers' gaspers on airborne disease transmission in aircraft cabins with personalized displacement ventilation. Numerical calculations were conducted in a seven-row, single-aisle, fully occupied, economy-class aircraft cabin with. This study first investigated the impact of source gasper direction and flow rate on the airborne transmission near the contaminant source. Then, the protective effect of the receptor's gasper was investigated. For a source passenger's gasper, the direction and flow rate of the gasper flow either increased or decreased the air contaminant transmission to other passengers. Directing the source gasper to the abdomen with a medium flow rate performed best by reducing the receptors' mean exposure index by at least 45%, as this approach minimized the contaminant circulation in the cabin. Turning on a receptor passenger's gasper could be an effective strategy to protect the receptor, and the working mechanism was revealed. The gasper-induced jet flow entrained the surrounding air into the jet region, and the protective effect was related to the contaminant concentration at ceiling level. With a suitable gasper direction and flow rate, the gasper jet formed a virtual barrier between the source passenger and the receptor. When the contaminants were transported upwards to a receptor's breathing zone, turning on the receptor's gasper reduced the contaminant concentration, since the downward gasper jet altered the airflow pattern in front of the receptor. The above study only focused on the impact of a single gasper, while the remaining gaspers in the cabin were assumed to be closed. However, the real situation involves concurrent operation of gaspers by passengers. The interaction between the main airflow and the multiple gasper-induced jet flows inevitably increases the complexity of the contaminant transmission in the cabin. To identify an executable gasper operation strategy by which passengers can control the transmission of airborne diseases, this study performed CFD simulation in a seven-row section of a single-aisle, fully occupied, economy-class aircraft cabin with a personalized displacement ventilation system. First, a seat-type-dependent gasper operation strategy based on the working mechanism of a single gasper was proposed. Next, random gasper operation under realistic conditions was used as the benchmark to evaluate the performance of the proposed gasper operation strategy. The results showed that the effectiveness was sensitive to the seat type of the source and the locations of the passengers. Specifically, when the source passenger was in the window seat or middle seat, the proposed strategy increased the exposure risk for the passengers in front of the source, and on the same side of the aisle as the source passenger. Meanwhile, for passengers in other seats, opening the gaspers in accordance with the proposed operation strategy was effective in controlling the contaminant transmission. When the source passenger was in the aisle seat, there was no significant difference between the proposed strategy and random operation in controlling the transmission. The above findings suggest that it is challenging for passengers to manually adjust their gaspers to effectively mitigate infection risk. Therefore, the key question should be answered: is there a centralized control mode of the gasper system feasible for mitigating airborne contaminant transmission? Moreover, since the gasper system is originally designed to improve individual comfort, the performance of the centralized control mode of the gasper system in maintaining passengers' individual comfort preference should also be considered. To address the above gaps, this study used CFD simulations to evaluate the centralized control mode of the gasper system in a seven-row section of a single-aisle, fully occupied, economy-class aircraft cabin with personalized displacement ventilation. Two centralized control modes were proposed, full control of engaged gaspers, and partial control of engaged gaspers. The no-control mode was used as the benchmark case. The results show that under full control of engaged gaspers, the number of relatively high-risk passengers was effectively reduced by 83%, 79% and 97% when the source passenger was in the window, middle, and aisle seat, respectively, compared with the number of cases under the no-control mode. However, the gasper open ratio and flow direction distributions significantly differed from those under the no-control mode. Under partial control of engaged gaspers, the number of relatively high-risk passengers was effectively reduced by 81%, 66% and 88% for each source location. Meanwhile, individual comfort preference was maintained for the majority of passengers. These findings demonstrate the feasibility of partial-control mode to achieve both airborne infection mitigation and comfort preferences in realistic cabin environments. Overall, this thesis systematically investigated the operation of gaspers for reducing airborne disease transmission in commercial airliners with personalized displacement ventilation system. Firstly, experimental measurements of both airflow and contaminant concentration distributions were conducted in a mock-up of an aircraft cabin to validate the CFD simulation results. Secondly, the validated CFD method was used to numerically investigate the influence of gasper direction and flow rate on the contaminant transport near the source and receptor passengers. Thirdly, a seat-type-dependent gasper operation strategy was proposed based on the working mechanism of a single gasper to provide practical guidance for passengers. Fourthly, since the gasper system is originally designed to improve individual comfort, this study proposed and evaluated a centralized control mode that could achieve both airborne infection mitigation and individual comfort preference in realistic cabin environments. The achievements of this thesis are expected to be implemented in actual aircraft cabins through automation control devices to execute the optimal gasper operations, thereby improving the cabin environment.