Experimental and numerical study of the air distribution in an airliner cabin

Nowadays, more people, including those with impaired health or who are otherwise potentially sensitive to the cabin environment, are traveling by air than ever before. The flying public demands a higher comfort level and a cleaner environment because they encounter a combination of environmental factors including low humidity, low air pressure, and sometimes, exposure to air contaminants such as ozone, carbon monoxide, various organic chemicals, and biological agents. Moreover, international air travel has increased the potential risks associated with airborne disease transmission and the release, whether accidentally or intentionally, of noxious substances during flight. Many studies suggest that the risk of infection during air travel is related to the cabin environment. In commercial airliner cabins, a thermally comfortable and healthy cabin environment is created by air distributions that are used to regulate air temperature and air velocity and to provide adequate ventilation for reducing gaseous and particulate concentrations of contaminant. The facts shown above leave an element of doubt whether the air distribution in airliner cabins is acceptable. Therefore, it is essential to study how the air is distributed in the air cabins to ensure that the cabin environment is safe, healthy, and comfortable for the flying public. This investigation firstly reviewed the methods used in predicting, designing, and analyzing air distributions in the cabins. Two popular methods are experimental measurements and numerical simulations. 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 effectively provide detailed information. Numerous applications using the two methods can be found in the literature for studying air distributions in aircraft cabin, including investigations on more reliable and accurate turbulence models. Our review shows that studies using both experimental measurements and computer simulations are becoming popular. Our review also found that it is necessary to use a full-scale test rig to obtain reliable and high quality experimental data, and that the hybrid CFD models are rather promising for simulating air distributions in airliner cabins. This investigation then experimentally studied the air distributions in the first-class cabin of a functional MD-82 aircraft and compared it at unoccupied and fully-occupied conditions. Heated manikins were used to simulate seated passengers. The experiment applied ultrasonic anemometers (UA) to measure the three-dimensional air velocity field and 64 thermo-couples to obtain air temperature field. UA works at 20 Hz, so the measured data could also be used to determine the turbulence intensity of the air. It was found that the flow fields were of low speed and high turbulence intensity. A combination of hot-sphere anemometers (HSA) and UA were applied to obtain the air velocity magnitude, air velocity direction, and turbulence intensity at the diffusers. The measured results indicate that the flow boundary conditions in this real aircraft cabin were rather complex and the velocity magnitude, air velocity direction, and turbulence intensity varied significantly from one slot opening to another. This study compared the flow fields of different occupation conditions in a real commercial airplane and provided high quality data for evaluating Computational Fluid Dynamics (CFD) models, including boundary conditions of diffusers and high-resolution flow and temperature fields. The third part of this investigation evaluated three turbulence models in different categories: the Re-Normalization Group (RNG) k-ϵ model, Large Eddy Simulation (LES), and Detached Eddy Simulation (DES) based on the measured steady-state flow fields under unoccupied and fully-occupied conditions in the first-class cabin of the functional MD-82 commercial airliner. By comparing the data of the two experimental conditions with the computed results from these three turbulence models, this study found that the RNG k-ϵ model gave acceptable accuracy in predicting the airflow in the unoccupied cabin where the flow was simple, but not for the complicated flow in the fully-occupied cabin. The DES gave acceptable flow fields for both conditions. The LES performed the best and the results agreed well with the experimental data. The comparisons also showed that the errors in the experimental data were more significant than that in the turbulence models