Investigation Of Longitudinal Airflow Characteristics In An Aircraft Cabin Based On The Angle Of Attack

With the steady improvement of the national economic level,civil airliner has gradually entered thousands of households.After the National Health Commission announced the official’under Category B management’of the novel coronavirus,the cross-regional flow of people across the country has soared,and air travel has become a travel choice for more people.Therefore,the attention of cabin safety and comfort will be further improved.The interior space of the aircraft cabin is relatively small,and the longitudinal length is large.The coupling effect of the thermal plume generated by the passenger heating and the air supply jet causes the complex unsteady flow characteristics inside the cabin.Being in a closed cabin environment for a long time is also easy to cause the spread of some respiratory viruses.Therefore,a reasonable airflow organization design not only ensures the cabin comfort but also ensures the personal safety of the crew.In order to improve the reduction degree of the cabin environment and ensure the operability of the experiment,most scholars have adopted a 1:1 partial cabin model.Therefore,in the study of longitudinal scale related problems,the real cabin environment cannot be reflected,resulting in few studies on longitudinal airflow.To guarantee sufficient lift during flight,the aircraft cabin must achieve a certain angle of attack with the horizontal direction.Due to the objective difficulties in experimental operation,there is no research on the flow field of engine room related to angle of attack.In the inclined rectangular cavity with heat source at the bottom,it is easy to form vortex current in the longitudinal direction.The existence of longitudinal airflow causes a certain risk of contaminant transportation.Therefore,this paper takes the whole cabin model of 28 rows as the research object,and takes the effect of the angle of attack into consideration to study the longitudinal flow field characteristics of the cabin.The research method of experimental research combined with numerical simulation has been widely used in the field of aircraft cabin.The reliability of the numerical simulation scheme is verified by the experimental data,so that the simulation can obtain more accurate prediction results.In terms of experiment,this study set up a 28-row cabin model of Boeing 737-800 in a 1:10 scale,using simplified human body and laying resistance wires to simulate human heating.The experimental condition is the cruising stage（angle of attack=8°）.The airflow temperature,temperature and CO2 tracer gas concentration were measured.The numerical simulation is realized by the computational fluid dynamics（CFD）.The large eddy simulation（LES）transient solution is used and this turbulence model has a better performance in revealing the flow field characteristics of the cabin.The component transport model is turned on to simulate the release of CO₂ gas.According to the results of experimental measurement and numerical simulation,this paper analyzes the unsteady flow characteristics of the aircraft cabin based on the angle of attack from the aspects of temperature field,velocity field and vortex structure.The results show that the velocity and temperature within a longitudinal section of an aircraft increase as the angle of attack increases.Compared with that during the horizontal state（angle of attack 0°）,the longitudinal airflow is enhanced under a larger angle of attack,exhibiting an overall trend of forwards airflow.The longitudinal airflow strengthens large vortex separation at the top of the cabin.The vortex structure shows high instability at different times and in different parts of the aircraft.The environmental control system of aircraft cabin is designed to suppress longitudinal airflow and reduce the risk of passenger infection.In this paper,CO₂ tracer gas method and CFD method are used to further verify the characteristics of longitudinal airflow and reveal the transportation law of contaminant.It is found that under the action of longitudinal airflow,the diffusion direction of contaminant is from the release source position forward,and the concentration decreases with the transportation distance.Passengers in the first two rows of the release source have the highest exposure risk,and passengers in the back row are almost unaffected.The larger scale vortex structure will limit the diffusion of contaminant.