Simulation And Inverse Design On Air Distribution In Commercial Airliner Cabins

Nowadays,more and more people are traveling by air than ever before.Many studies suggest that the discomfort and 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.Therefore,this investigation aims to study how the air is distributed in the aircraft cabins and conduct further inverse design to ensure that the cabin environment is safe,healthy,and comfortable for the flying public.To achieve the above objectives,this study conducted the following investigations:1)This investigation 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 the 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.With the high quality data including boundary conditions of diffusers and high-resolution flow and temperature fields,this investigation then evaluated three turbulence models in different categories.The validated turbulence model was further used for the design of the cabin environment.2)With the validated turbulence model,this study then developed the CFD-based adjoint method that can be used for inverse design of enclosed environment.The method can inversely identify the air supply location,size,and parameters.The design objective could be local air distribution.The developed CFD-based adjoint method was implemented in OpenFOAM,which is a CFD toolbox and can be used to simulate a broad range of physical problems.This study further validated the CFD-based adjoint method by experimental data from literature and applied the method to find the optimal design variables of air supply locations,size,and parameters for a single-aisle airliner cabin to design a desired thermal environment.3)To speed up the design procedure,this study employed the fast fluid dynamics to solve the Navier-stokes equations.This study implemented FFD in OpenFOAM and used a local searching method that made the FFD solver applicable to unstructured meshes.Because the split scheme used in FFD is not conservative,this investigation developed a combined scheme that used split scheme for the continuity and momentum equations and iterative scheme for scalar equations.The combined scheme ensures conservation of the scalars.This investigation validated the FFD solver by experimental data from literatures.The above investigations lead to the following conclusions:(1)the measurements found significant longitudinal flow in the cabin.The air distributions also illustrate high decay of turbulence kinetic energy from the diffusers to the occupied area.The thermal plumes from the heated manikins had little influence on the turbulence.The temperature fields in the fully-occupied cabin condition stratified;(2)The LES and DES had better performance in predicting the flow and the RNG k-ε model had the worst performance.Since LES and DES used at least 20 times more computing time than the RNG k-ε model,the RNG k-ε model is preferred;(3)The CFD-based adjoint method could inversely identify air supply conditions or improve the thermal comfort in an aircraft cabin.With different constraints used,the air supply location,size,and parameters found can be very different.The computing costs did not vary with the number of design variables;(4)The FFD simulations with the structured and unstructured meshes predicted similar air velocity and temperature fields,and the predicted results agreed well with the experimental data.