Influences of the Fresh Air Volume on the Removal of Cough-Released Droplets in a Passenger Car of a High-Speed Train Using CFD

The spread and removal of pollution sources,namely,cough-released droplets in three different areas(front,middle,and rear areas)of a fully-loaded passenger car in a high-speed train under different fresh air flow volume were studied using computational fluid dynamics(CFD)method.In addition,the structure of indoor flow fields was also analysed.The results show that the large eddies are more stable and flow faster in the air supply under Mode 2(fresh air volume:2200m3/h)compared to Mode 1(fresh air volume:1100m3/h).By analysing the spreading process of droplets sprayed at different locations in the passenger car and with different particle sizes,the removal trends for droplets are found to be similar under the two air supply modes.However,when increasing the fresh air flow volume,the droplets in the middle and front areas of the passenger car are removed faster.When the droplets had dispersed for 60s,Mode 2 exhibited a removal rate approximately 1%–3%higher than Mode 1 for small and medium-sized droplets with diameters of 10 and 50μm.While those in the rear area,the situation is reversed,with Mode 1 slightly surpassing Mode 2 by 1%–3%.For large droplets with a diameter of 100μm,both modes achieved a removal rate of over 96%in all three regions at the 60 s.The results can provide guidance for air supply modes of passenger cars of high-speed trains,thus suppressing the spread of virus-carrying droplets and reducing the risk of viral infection among passengers.

Impact of a Bundle on Prevention and Control of Healthcare associated Infections in Intensive Care Unit

Inpatients in the intensive care unit（ICU） are at high risk for healthcare-associated infections（HAIs）. In the current study, a bundle of interventions and measures for preventing and controlling HAIs were developed and implemented in the ICU by trained personnel, and the impact of the bundle was evaluated. The incidence of HAIs, the adjusted daily incidence of HAIs and the incidence of three types of catheter-related infections before and after the bundle implementation were compared. The execution rate of the bundle for preventing and controlling ventilator-associated pneumonia（VAP） was increased from 82.06% in 2012 to 96.88% in 2013. The execution rate was increased from 83.03% in 2012 to 91.33% in 2013 for central line-associated bloodstream infection（CLABSI）, from 87.00% to 94.40% for catheter-associated urinary tract infection（CAUTI）, and from 82.05% to 98.55% for multidrug-resistant organisms（MDROs）, respectively. In total, 136 cases（10.37%） in 2012 and 113 cases（7.72%） in 2013 involved HAIs, respectively. Patients suffered from infection of the lower respiratory tract, the most common site of HAIs, in 134 cases（79.29%） in 2012 and 107 cases（74.30%） in 2013 respectively. The incidence of VAP was 32.72‰ and 24.60‰, the number of strains of pathogens isolated was 198 and 173, and the number of MDROs detected in the ICU was 91 and 74 in 2012 and 2013, respectively. The percentage of MDROs among the pathogens causing HAIs was decreased in each quarter of 2013 as compared with the corresponding percentage in 2012. In 2013, the execution rate of the bundle for preventing and controlling HAIs was increased, whereas the incidence of HAIs and VAP decreased as compared with that in 2012.

Smoke movement in a tunnel of a running metro train on fire

Research on the distribution of smoke in tunnels is significant for the fire emergency rescue after an operating metro train catches fire. A dynamic grid technique was adopted to research the law of smoke flow diffusion inside the tunnel when the bottom of a metro train was on fire and to compare the effect of longitudinal ventilation modes on the smoke motion when the burning train stopped. Research results show that the slipstream curves around the train obtained by numerical simulation are consistent with experimental data. When the train decelerates, the smoke flow first extends to the tail of the train. With the decrease of the train's speed, the smoke flow diffuses to the head of the train. After the train stops, the slipstream around the train formed in the process of train operation plays a leading role in the smoke diffusion in the tunnel. The smoke flow quickly diffuses to the domain in front of the train. After forward mechanical ventilation is provided, the smoke flow inside the tunnel continues to diffuse downstream. When reverse mechanical ventilation operates, the smoke in front of the train flows back rapidly and diffuses to the rear of the train.

Review of research on high-speed railway aerodynamics in China

High-speed railway aerodynamics is the key basic science for solving the bottleneck problem of high-speed railway development.This paper systematically summarizes the aerodynamic research relating to China’s high-speed railway network.Seven key research advances are comprehensively discussed,including train aerodynamic drag-reduction technology,train aerodynamic noise-reduction technology,train ventilation technology,train crossing aerodynamics,train/tunnel aerodynamics,train/climate environment aerodynamics,and train/human body aerodynamics.Seven types of railway aerodynamic test platform built by Central South University are introduced.Five major systems for a high-speed railway network—the aerodynamics theoretical system,the aerodynamic shape(train,tunnel,and so on)design system,the aerodynamics evaluation system,the 3D protection system for operational safety of the high-speed railway network,and the high-speed railway aerodynamic test/computation/analysis platform system—are also introduced.Finally,eight future development directions for the field of railway aerodynamics are proposed.For over 30 years,railway aerodynamics has been an important supporting element in the development of China’s high-speed railway network,which has also promoted the development of high-speed railway aerodynamics throughout the world.