key: cord-0686233-8r59z4u4
authors: Zhang, Yongzhi; Li, Jiayu; Liu, Mingxin; Liu, Junjie; Wang, Congcong
title: Experimental investigation of large-scale flow structures in an aircraft cabin mock-up
date: 2020-08-29
journal: Build Environ
DOI: 10.1016/j.buildenv.2020.107224
sha: e28e4fd9d1fd08577c013472cfa76f57ccd6086d
doc_id: 686233
cord_uid: 8r59z4u4

The purpose of this study was to investigate the influence of large-scale circulation on the flow field in a cabin mockup. The velocity was measured by ultrasonic anemometers (UA). Then, this study analyzed the turbulence kinetic energy spectra of the velocity fluctuation signal. The turbulence kinetic energy spectra of the measurement points reflect the flow characteristic of the large-scale circulation in the cabin mockup. The results contribute to the understanding of the role of the thermal plume on the large-scale circulation in the cabin. The large-scale circulation's impact on air quality was also investigated, and the contaminant distribution was measured using tracer gas in the cabin. The two large-scale circulation interactions made the air flow mixing approximately uniform.

The civil airliner is an important means of transport that has greatly reduced 2 people's travel time. Increasing numbers of people use aircraft for travel. The aircraft 3 brings convenience to passengers but has also increased air quality problems [1] . The 4 cabin environment has a high density of occupants, increasing the risk of passenger 5 cross-infection [2] . There is a mutual coupling effect between the supply-air jet and 6 the human thermal plume, an effect which makes the flow field more complicated in 7 the cabin. Therefore, investigating the flow characteristics within the cabin is 8 necessary during commercial passenger flights [3] . A mixing ventilation system is 9 commonly used in the aircraft cabin; the system consists of air supply at the top of the models were well suited for indoor large-scale circulation ventilation problems [13] . 2 The room geometry can be used to distinguish between unstable to stable room 3 airflow structures [35] . Through Yan's experiment and computational fluid dynamics 4 (CFD), it was found that the location of the pollution source had a significant effect 5 on the transport of pollutants in the cabin [14] . It was also found that an increased 6 ventilation rate does not necessarily protect the passengers close to the source. This is 7 due to the characteristics of the large-scale circulation of the flow field. 8 To fully understand the complex airflow in the cabin, it is necessary to fully 9 study the characteristics of large-scale circulation. Knowledge of the spatial and 10 temporal characteristics of large-scale circulation is becoming increasingly important.

The related research can guide the design of the cabin. The thermal plume and 12 supply-air jet momentum-driven flow have highly complex structures. Bosbach et al. 13 analyzed the interactions between supply-air jets and thermal plumes under two The high thermal load due to high occupant density has an effect on the flow 23 field that is comparable in importance to the supply air jet. These competing flows 24 cause instability. [20] [21] [22] . Due to the heat dissipation of the passengers, the thermal 25 boundary condition of the cabin's thermal environment was similar to 26 Poiseuille-Rayleigh-Benard (PRB) mixed convection flows [23] . From a technical 27 point of view, the dynamics of the large-scale circulation and the effect of spatial 28 distribution on thermal convection are very important [24] . In addition, the large-scale 29 circulation was constantly fluctuating during the exercise [25] . The large-scale 30 J o u r n a l P r e -p r o o f circulation was driven mainly by the supply-air jet in the cabin. The airflow 1 dissipation downstream occurred at a lower frequency, which was due to the 2 turbulence dissipation spectra [26, 27] . The instantaneous velocity vector field 3 obtained by the particle image velocity (PIV) can detect the core and center position 4 of the large-scale circulation through a proper orthogonal decomposition algorithm.

The three-dimensional nature of the large-scale circulation structure is represented by 6 the irregular oscillating shape of the core line [28, 29] . 7 Spectral analysis is a commonly used method to study velocity fluctuation. The 8 turbulence kinetic energy spectra index is an important parameter for characterizing 9 the energy distribution on the double logarithmic power spectral density curve. The the spectral curve with the Re number of the supply-air jet was investigated [33] . It 7 was found that the spectrum has a distinct inertial subregion only after the critical 8 Reynolds number is exceeded.

The performance of large-scale flow structures was studied in an aircraft cabin (2) Tracer gas measurement 15 To investigate the large-scale circulation impact on the cabin environment, the 16 contaminant distribution was measured using tracer gas in the cabin. Sulfur 3. Results and discussion 10 The turbulence kinetic energy spectra of the two cases have similar results, as 11 shown in Figure 5 . In particular, the turbulence kinetic energy spectra of case 1 12 (points 2, 3, 4 and 5) and case 2 (points 7, 8, 9 and 10) are almost the same. Therefore, 13 the results imply the turbulence kinetic energy spectra of the measurement points Figure   1 2. It still has high energy. This is due to the center position of the large-scale 2 circulation constantly fluctuating during movement. The velocity magnitude and 3 direction are also fluctuating. Therefore, the average velocity is smaller. Moreover, 4 the circulation has low turbulence kinetic energy at the entrainment process (point 4).

At that point, the turbulent vortex structure breaks into a small-scale vortex structure, 6 the peak of the turbulent kinetic energy spectrum disappears. The airflow mixed with 7 supply-air jet flow through circulation entrainment. As shown in Figure 6 , the turbulence kinetic energy spectra of cooling condition condition, as shown in Figure 7 (2). This is because the passenger's thermal plume 28 effect is small. Fig. 9 Contaminant concentration distribution around passengers Firstly, the turbulence kinetic energy spectrum analysis method can well reveal 

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