Characteristics Of Unsteady Flow In A Long And Narrow Enclosed Cabin

With the rapid development of society and economy,airplanes have become the transportation mode of choice for more people.At the same time,people have begun to pursue comfort and safety in travel.Issues such as the thermal environment and airflow distribution in the engine room have attracted more attention.Since the cabin is a closed,narrow,and crowded special space,these factors complicate the flow field in the cabin.The densely populated environment such as aircraft cabins is common in our lives.For example,high-speed rail train cars,ship cabins,and special construction environments such as hospital wards and assembly houses also have similar air thermal fluid phenomena and laws.In this type of environment,due to the dense distribution of people,the indoor thermal buoyancy has a great influence on the flow field structure.The engine room is a closed space and is less affected by external factors.When there is a temperature difference between top and bottom in the narrow and long enclosed cabin,multiple unstable vortices will be generated in the longitudinal direction of the enclosed cabin.The appearance of longitudinal vortex will not only cause the unsteady flow of airflow,but also cause the difference in thermal comfort of different rows of passengers inside the cabin.Therefore,this paper uses cabins as a typical environment to study the characteristics of unsteady flow in long and narrow closed cabins.The method of combining experiment and simulation is the key to obtaining the air distribution in the cabin of the aircraft.Experimental measurement is the most accurate method to obtain the airflow organization.Comparing the deviation between the measured experimental value and the simulation result,the agreement between the experimental value and the simulation result can carry out a more complete and comprehensive study of the flow field in the engine room.In terms of experimental research,based on the actual aircraft cabin size,this research designed a 10:1 narrowlength and reduced-ratio cabin model,and built an experimental platform including a constant temperature room,a reduced-ratio cabin model,an air supply system,and a measurement system,in which the human body was reasonably simplified into squares.And lay resistance wires to imitate the heating of the cabin personnel,and then measure and analyze the cabin temperature and speed;in terms of numerical simulation,combined with the actual size of the experimental platform to establish a model,the three turbulence models provided by FLUENT(RNG k-ε,LES,DES)for comparison and verification.The results show that the results obtained by the LES model are closer to the experimental results and can more truly reflect the unsteady flow in the narrow and long enclosed cabin.Based on the results of experiments and simulations,this paper analyzes the airflow characteristics in the reduced ratio model of the cabin from the four aspects of temperature field,flow field,vortex structure and comfort when the cabin is full.The results show that under the condition that the boundary conditions of the air supply on both sides are exactly the same,due to the combined effect of the jet collision and the thermal plume of the human body,the lateral-scale temperature field and the flow field appear asymmetry in the enclosed cabin.The gas loss is stable on the longitudinal scale,resulting in a large number of unstable discrete vortex structures.Compared with the actual size of the aircraft cabin data,the scaled-down model is also suitable for predicting the thermal comfort of the human body in the cabin.The airflow uniformity in the narrow and long enclosed cabin under the side air supply mode is good,and the thermal comfort is generally cold.This article further explores the mechanism of unsteady flow in a long and narrow enclosed cabin driven by a heat source on the bottom surface in an empty cabin.The results show that the asymmetric flow phenomenon in the horizontal scale of the empty cabin is similar to that in the full cabin,and is a common flow feature in the narrow and long enclosed cabin.There will be periodic high temperature areas on the longitudinal scale.The unstable thermal convection in the high temperature area makes the longitudinal direction of the air flow unstable.The high temperature control area is about 2 times the cabin height and 1.3 times the cabin width.