Flow field characteristics in high-speed train cabin: Negative effect of non-vertical air supply

Abstract

Ventilation systems are critical for improving the cabin environment in high-speed trains, and their interest has increased significantly. However, whether air supply non-verticality deteriorates the cabin air environment, and the flow mechanism behind it and the degree of deterioration are not known. This study first analyzes the interaction between deflection angle and cabin flow field characteristics and ventilation performance. The results revealed that the interior temperature and pollutant concentration decreased slightly with increasing deflection angle, but resulted in significant deterioration of thermal comfort and air quality. This is evidenced by an increase in both draught rate and non-uniformity coefficient, an increase in the number of measurement points that do not satisfy the micro-wind speed and temperature difference requirements by about 5% and 15%, respectively, and an increase in longitudinal penetration of pollutants by a factor of about 5 and the appearance of locking regions at the ends of cabin. The results also show that changing the deflection pattern only affects the region of deterioration and does not essentially improve this deterioration. This study can provide reference and help for the ventilation design of high-speed trains.

1. Introduction

Due to the breakthroughs in various key technologies and the improvement of equipment and facilities, the importance of high-speed trains is gradually increasing [1]. A positive cabin environment is the key to ensure the green operation of the railroad and the comfort and health of passengers, and people's concern and demand for this is gradually increasing. As early as about a hundred years ago, people carried out a lot of researches for the good environment of the airplane cabin. With the development of science and technology, many related advanced scientific concepts, techniques and methods have been applied to the optimization of cabin design. To improve the indoor air environment, scholars have conducted many scientific studies from various aspects. These include, but are not limited to: research on the mechanism of flow field action [2, 3]; research on the mechanism of virus diffusion [4−6]; air vent layout [7, 8]; personalized ventilation [9, 10]; air supply uniformity [11]; diffuser optimization [12]; ventilation parameter optimization [13]; and multi-objective optimization [14]. These researches have made great contributions to create good air quality.

Relevant studies have shown that good ventilation can directly improve the indoor air environment, enhance thermal comfort and reduce airborne propagation. LU et al [15] utilized an improved proper orthogonal decomposition reconstruction method for the ventilation performance of high-speed trains to optimize design. By optimizing the three design variables of air supply speed, air supply temperature and air supply angle, the cabin air quality is ultimately improved. XU et al [16] investigated the effects of four ventilation methods on the diffusion characteristics of cough droplets in the passenger compartment of a high-speed train. The results showed that the potential infection risk in the passenger cabin was smaller when top air supply was used, and the longitudinal transport capacity of the disease could be suppressed more effectively. SCHMELING et al [17] used experimental means to investigate the effects of five ventilation methods on thermal comfort in the cabin of a high-speed train, and proposed a novel low-momentum ventilation concept, which was shown to have a great potential for improving thermal comfort. WU et al [18] investigated the formaldehyde distribution characteristics in the cabin of a high-speed train using numerical simulation. The resu