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Passenger thermal comfort in high-speed train (HST) carriages presents unique challenges due to factors such as extensive operational areas, longer travel durations, larger spaces, and higher passenger capacities. This study aims to propose a new prediction model to better understand and address thermal comfort in HST carriages. The proposed prediction model incorporates skin wettedness, vertical skin temperature difference (ΔTd), and skin temperature as parameters to predict the thermal sensation vote (TSV) of HST passengers. The experiments were conducted with 65 subjects, evenly distributed throughout the HST compartment. Thermal environmental conditions and physiological signals were measured to capture the subjects' thermal responses. The study also investigated regional and overall thermal sensations experienced by the subjects. Results revealed significant regional differences in skin temperature between upper and lower body parts. By analyzing data from 45 subjects, We analyzed the effect of 25 variables on TSV by partial least squares (PLS), from which we singled out 3 key factors. And the optimal multiple regression equation was derived to predict the TSV of HST occupants. Validation with an additional 20 subjects demonstrated a strong linear correlation (0.965) between the actual TSV and the predicted values, confirming the feasibility and accuracy of the developed prediction model. By integrating skin wettedness and ΔTd with skin temperature, the model provides a comprehensive approach to predicting thermal comfort in HST environments. This research contributes to advancing thermal comfort analysis in HST and offers valuable insights for optimizing HST system design and operation to meet passengers' comfort requirements. [ABSTRACT FROM AUTHOR]

The high-speed train's windshield structure is vital to the boundary layer development and drag reduction design. Up to date, windshield structures are assumed as rigid body in most train aerodynamic numerical simulations. This research investigates the fluid-solid coupling effect of high-speed train's windshield structure based on an 8-car formation model. The influence of speed level and windshield installation location on the flow field parameter and windshield deformation profile are systematically analysed. The results indicate that, with the development the boundary layer, the time-averaged pressure coefficient, lateral force coefficient and windshield's displacement all gradually decrease from 1st windshield to 4th windshield along the stream direction. In the connecting region between the windshield and vestibule, a pair of negative pressure zone are formed and gradually intensify along the downstream direction, such that the time-averaged deformation, as well as the vibration amplitude of windshields experience a slight increase. According to the power spectral density analysis, the vibration frequency of all windshields' displacement varies between 10.25 Hz and 12.5 Hz. Meanwhile, the pantograph structure will lead to the generation of vortex group, these vortices will lead to additional small low frequency peaks for windshields installed on the downstream direction of pantograph. [ABSTRACT FROM AUTHOR]

In high-speed train operations, especially during the passage of two trains or when passing through tunnels, the surface of the train experiences intense transient alternating pressure. The resulting alternating aerodynamic loads can lead to fatigue damage in the train's structure. To address this issue, an experimental device is developed in this study to accurately replicate the alternating aerodynamic loads experienced by trains. In this research, a novel method for simulating variable loads using triangular pressure wave patterns is proposed. Validation tests are conducted to assess the effectiveness of the device in replicating the desired load profiles. Furthermore, a noise suppression mechanism is incorporated into the device design. By incorporating noise source analysis and optimization techniques, the device design effectively controls the noise level within 85 dBA during the loading process. The experimental results demonstrate that the proposed device can achieve a triangular wave loading frequency of 2.5 cycles per minute, with a pressure range of ±3000 Pa for a 250 m3 high-speed train cabin. The pressure load output stability has high consistency in the pressure‒time curves at various measurement points inside the tested object, with a maximum difference of 0.99%. The experimental device designed in this study meets the requirements for simulating the aerodynamic loads on the surface of high-speed trains travelling at speeds of up to 350 km/h. • Novel device accurately simulates aerodynamic alternating loads on high-speed trains. • Integrated mechanism maintains noise levels below 85 dBA during loading. • Achieves stable triangular wave loading, crucial for replicating aerodynamic stresses on train cabin.. [ABSTRACT FROM AUTHOR]

Heating, Ventilation, and Air Conditioning (HVAC) systems in high-speed trains (HST) are responsible for consuming approximately 70% of non-operational energy sources, yet they frequently fail to ensure provide adequate thermal comfort for the majority of passengers. Recent advancements in portable wearable sensors have opened up new possibilities for real-time detection of occupant thermal comfort status and timely feedback to the HVAC system. However, since occupant thermal comfort is subjective and cannot be directly measured, it is generally inferred from thermal environment parameters or physiological signals of occupants within the HST compartment. This paper presents a field test conducted to assess the thermal comfort of occupants within HST compartments. Leveraging physiological signals, including skin temperature, galvanic skin reaction, heart rate, and ambient temperature, we propose a Predicted Thermal Comfort (PTC) model for HST cabin occupants and establish an intelligent regulation model for the HVAC system. Nine input factors, comprising physiological signals, individual physiological characteristics, compartment seating, and ambient temperature, were formulated for the PTS model. In order to obtain an efficient and accurate PTC prediction model for HST cabin occupants, we compared the accuracy of different subsets of features trained by Machine Learning (ML) models of Random Forest, Decision Tree, Vector Machine and K-neighbourhood. We divided all the predicted feature values into four subsets, and did hyperparameter optimisation for each ML model. The HST compartment occupant PTC prediction model trained by Random Forest model obtained 90.4% Accuracy (F1 macro = 0.889). Subsequent sensitivity analyses of the best predictive models were then performed using SHapley Additive explanation (SHAP) and data-based sensitivity analysis (DSA) methods. The development of a more accurate and operationally efficient thermal comfort prediction model for HST occupants allows for precise and detailed feedback to the HVAC system. Consequently, the HVAC system can make the most appropriate and effective air supply adjustments, leading to improved satisfaction rates for HST occupant thermal comfort and the avoidance of energy wastage caused by inaccurate and untimely predictive feedback. • This paper presents thermal comfort model for high-speed train passengers based on skin temperature, galvanic skin response and electrocardiogram. • Differences in physiological signals and thermal sensation votes among different populations (Gender, BMI and position) were analyzed. • The features of the four combinations were used as input factors to obtain accuracy using different machine learning models. • Sensitivity analysis of the best prediction model (Random Forest) was performed using SHAP and DSA methods. [ABSTRACT FROM AUTHOR]

A moving model test method based on stagnation pressure measurements is proposed to measure the train aerodynamic drag coefficient. Because the front tip of a high-speed train has a high pressure area and because a stagnation point occurs in the center of this region, the pressure of the stagnation point is equal to the dynamic pressure of the sensor tube based on the obtained train velocity. The first derivation of the train velocity is taken to calculate the acceleration of the train model ejected by the moving model system without additional power. According to Newton’s second law, the aerodynamic drag coefficient can be resolved through many tests at different train speeds selected within a relatively narrow range. Comparisons are conducted with wind tunnel tests and numerical simulations, and good agreement is obtained, with differences of less than 6.1%. Therefore, the moving model test method proposed in this paper is feasible and reliable. [ABSTRACT FROM AUTHOR]

It has been observed that the condensing air flux through the air-conditioning (AC) unit on a running high-speed train significantly decreases due to the shear stream flowing over the train roof. Insufficient condensing air may put the AC under a risk of overheating. In this study, four shapes of flow deflectors that are able to alleviate the flux drop are designed and investigated using experimentally validated Delayed Detached Eddy Simulation (DDES). Numerical results show that the air flux drop mainly depends on the cross-sectional shape of deflectors, which changes the flow conditions above AC condensing outlets, including the properties of the negative pressure region and the incident angle of the high-speed shear flow produced by the train operation. Meanwhile, the extra aerodynamic drag brought by the installation of deflectors is computed and analyzed. The results presented in this paper can be applied to the design of the AC system, as well as other equipment requiring active convective cooling, on higher speed trains. • Established a numerical model that couples the slipstream of train and the condensing airflow driven by condensing fans. • Analyzed 4 types of flow deflectors that may alleviate the flux decrease while the fans are exposed to slipstream. • Presented the detailed flow characteristics in the vicinity of train and AC units. • Isolated the aerodynamic drag contributed by train body, AC operation, deflectors, and momentum change of condensing flow. [ABSTRACT FROM AUTHOR]

The aerodynamic forces of the high-speed train pantograph increase sharply with the increase in the operating speed. In this study, we simulated the unsteady aerodynamic performance of a high-speed train with the improved delayed detached eddy simulation (IDDES) method and analyzed the influence of the sinking height of the pantograph platform on the aerodynamic drag and lift coefficients of the high-speed train and pantograph. To verify the simulation model, the numerical results were compared with the wind tunnel test results, showing good agreement. The results indicated that the uncovered cavity formed by the pantograph platform sinking shielded the pantograph base frame to varying degrees, lowered the vorticity around it, but caused disturbances to the flow field near the train surface. The sinking platform of the pantograph effectively reduced the range and amplitude of the positive and negative pressure on the surfaces of pantograph base frame and cavity bottom. In addition, the pantograph drag and lift coefficients decreased with the increase in the sinking height. When the sinking height reached 500 ​mm, the aerodynamic drag and lift coefficients of the pantograph and the entire train decreased by 35.3%, 110.3%, 2.9%, and 21.4%, respectively. • Simulation of the unsteady aerodynamic performance of a high-speed train with IDDES method. • Investigation of effects of platform sinking height on the complex flow field around the pantograph. • Investigation of effects of the platform sinking height on the aerodynamic coefficients of the train and pantograph. [ABSTRACT FROM AUTHOR]

With increasing train speed, aerodynamic effects pose a safety risk for train operations, especially for trains passing each other, the strong transient aerodynamic loads could result in window breakage, sideward shaking, trackside worker injuries, and facility fatigue damage. Unsteady compressible numerical simulation is carried out in this paper to investigate the transient flow field induced by two maglev trains passing each other at a speed of 430 km/h in open air. Good agreement is obtained between the numerical method and full-scale experiment results, with differences smaller than 6%. The transient pressure change on train surfaces and the slipstream distributions on trackside are analysed. It was noted that the peak values of pressure coefficient for two trains passing each other are approximately twice as larger as that of a single train passing because of the blocking effect and interference by the motion of the other train in the opposite direction. The maximum slipstream velocity occurs at a height of 1.4 m from the top of rail (TOR) at the meeting position, and the relationship between the slipstream velocity and the distance from the centre of rail (COR) is obtained, based on which, the safe distance is calculated. [ABSTRACT FROM AUTHOR]

Abstract This study investigates the alleviation effect of partially enlarged cross-section on tunnel aerodynamics. By comparing the numerical results to moving model tests data, the SST k-ω turbulence model and hybrid grid are used for the numerical simulations of high-speed train passing through tunnel. The reduction effects of three parameters for the enlarged section are analyzed, i.e., length, cross-sectional area, and slope. Systematic numerical simulations show that the terminal location of the enlarged section should be close to the location of the initial compression wave amplitude along tunnel length direction. The reduction rates of the pressure transient amplitude and the average pressure variation follow a second order polynomial equation with the increase of the enlarged section area, and increase with the increase of enlarged section slope. Positive enlarged section slope is applied for reducing pressure transients in the tunnel. Furthermore, an engineering application equation is proposed, with which the reduction rates of enlarged sections on the pressure transient amplitude and the average pressure variation can be estimated effectively. The equation generalized in this study could well guide the tunnel design process. Highlights • The SST k-ω turbulence model with hybrid grid achieved best accuracy in simulation. • The optimum length of the enlarged section is obtained. • The relationship of pressure transients and cross-sectional area is derived. • An engineering equation regarding pressure transient reduction is proposed. [ABSTRACT FROM AUTHOR]

• Study the mitigation effect of pressure fluctuations caused by train intersection in a tunnel with the enlarged end. • Consider the effects of the total length of tunnels and unit number of trains on the optimal length of the enlarged section. • Analyse the mitigation principle of the pressure fluctuations impacted upon trains. • Obtain an optimal length coefficient to attain the maximum mitigation of the pressure fluctuations. Intense pressure fluctuations generated by the intersection of high-speed trains (HSTs) in a tunnel are unfavourable for the comfort of passengers and the safety of HSTs and tunnel facilities. This study numerically investigated the mitigation principle of the pressure fluctuation impacted upon HSTs using the enlarged tunnel end with taking into account the total tunnel length and the unit number of HSTs. Moving model tests were also performed to validate the numerical method based on the unsteady RANS equations and RNG k - ε turbulence model. The numerical results show that the enlarged end of a tunnel can manifestly alleviate the negative pressure induced by the train intersection and the length ratio of the optimal length of the enlarged section to the total length is in the range of 0.26–0.28. The optimal length of the enlarged section can be implemented by synchronising the contact of the derived waves with the train intersection. Moreover, the increase in the marshalling number of HST augments the mitigation effect of the enlarged section. This study gives insight into the mitigation of the pressure fluctuation in tunnels and can provide valuable data and a theoretical basis for the tunnel design when considering the aerodynamic effect of HST intersection. [ABSTRACT FROM AUTHOR]

With the increase in the speed of metro trains, the aerodynamic effects caused by the train passing through the tunnel, especially the pressure change, will be significantly enhanced. This pressure will have a significant effect on the auxiliary facilities in the tunnel and the passengers in the carriage. Based on the sliding grid technique, Fluent software was used to simulate the aerodynamic performance of six trains passing through different shield transfer structures, and the influences of the shield cross-section area, length, and form on train aerodynamic performance were studied. The results show that when the cross-sectional area of the shield transfer structure increases from 42 m2 to 62 m2, the positive pressure peak P max on the train surface increases significantly, and the peak-to-peak value and positive pressure gradient peak in the large-section tunnel are increased by 20.50 % and 106.83 %, respectively; when the length of the shield transfer structure is increased from 80 m to 120 m, the positive pressure peak and pressure gradient peak in the large-section tunnel are increased by 22.53 % and 21.70 %, respectively; for constant cross-sectional area and ellipsoidal structural forms, the slanting structural form has a smaller train surface pressure amplitude as well as a smaller peak pressure and peak pressure gradient in a large-section tunnel. These findings will contribute to the design of shield transfer structure in subway and tunnel systems. [ABSTRACT FROM AUTHOR]

A moving model (1/20 scale) was used to study the effect of high temperature at the entrance of a tunnel on the aerodynamic performance of a high-speed train passing through it. The air in the tunnel was heated using highly-precise, self-controlling, ultra-thin, silicone rubber heating devices that were firmly attached to the inner surface of the tunnel (covering the first 2 ​m of the tunnel from the entrance). When the specified temperature was reached, tests were performed using a model train moving at different speeds. The experimental results were used to compare and analyze the pressure fluctuations and propagation of pressure waves under normal and localized high-temperature conditions. The results show that the peak-to-peak value of the transient pressure on the tunnel surface decreases by 5–7% in the presence of a normal ambient and high temperature tunnel mode. In addition, the corresponding difference on the surface of the head of the train is 3–4%. Hoping this experimental study will encourage theoreticians to investigate the mechanism responsible for the generation of transient pressures in localized high temperature railway tunnels. The results can provide guidance and support for researchers seeking to improve passenger safety and comfort in high temperature railways. • Study the influence of the local high temperature difference by a moving model test. • Obtain the aerodynamic performance of trains passing through the tunnel under heat. • Compare the pressure curve difference between normal temperature and heating. • Analyze the difference of the pressure change and pressure propagation characteristic. • Study the pressure peak-to-peak difference under normal and heating. [ABSTRACT FROM AUTHOR]

Alleviation of the pressure transients caused by high-speed trains intersecting in a tunnel with partially reduced cross-section is investigated by numerical simulation. The RNG k - ε turbulence model and hybrid grid are adopted for the numerical simulation, which is validated by the moving model test. Two factors, the length of reduced section (L) and the train marshalling number, are considered to analyse the alleviation effect. The results show that, for reduction of the pressure transients induced by the intersection of three-car marshalling trains, the location of the change in cross-section is supposed to be near the location of the maximum value of the initial expansion wave (L → 240 ​m). In addition, for four-car marshalling trains intersecting in a tunnel of L ​= ​240 ​m, the excavation volume of the tunnel (tunnel volume) decreases by 14.4%, and the average pressure amplitude on the train surface decreases by 7.9%. Especially the pressure amplitude at the measurement point in the streamlined area of the tail car decreased by 28.6%. The reduced section tunnel has a good effect on decreasing the pressure transients around train body and the tunnel excavation volume (construction cost), which helps the tunnel design process. • The influence of the reduced section on the pressure transients in high-speed train tunnels are analysed. • For high-speed trains intersecting in the tunnel, the optimal location of the change in cross-section are obtained. • The excavation volume of the tunnel and the average train surface pressure amplitude decreases by 14.4% and 7.9%. [ABSTRACT FROM AUTHOR]

Abstract The air-conditioning units (ACUs) on high-speed trains are responsible for cooling the passenger compartment. Insufficient condensing air flux through the ACU may lead to a suboptimal cooling and causes dangerous levels of overheating or even a shutdown of the ACU itself. In this paper, the air flow through ACU at different speeds of a high-speed train is investigated numerically. A significant drop of the condensing air flux during the train operation at higher speed is observed. This phenomenon is related to the interaction of the air flow through the ACU and the boundary layer on the roof of the train. Simulations show that the motion of the train creates a region of negative pressure above the ACU inlets and a region of positive pressure above the outlets. Thus, a particular structural optimization of the air outlets aimed at reducing the pressure buildup is proposed. The proposed numerical method can be used serve to investigate and to optimize the performance the ACUs on high-speed trains under different structural modifications. [ABSTRACT FROM AUTHOR]

• History of aural sensations was visualized during the train's running in tunnels. • Effect of speed, seal index, car No. and tunnel length on ear comfort was revealed. • Ear sensations were classified into four levels based on the duration of discomfort. • Mathematic model was established to predict pressure-related ear comfort in trains. • A way to seek for preferable speeds was put forward for given train and rail lines. Aural comfort is negatively affected during a train's passage through various tunnel environments. The objective of this study was to propose a prediction model for determining optimal operation parameter combinations to improve train occupants' aural comfort. High-speed train model tests, combined with a mathematical transfer model, were used to obtain the interior pressure transients under varying speeds, tunnel lengths and seal indexes. Then, a middle ear finite element model was used to simulate the dynamic responses under the pressure transients, and three indicators were employed to assess the severity of aural sensations. Meanwhile, the aural discomfort were classified into four groups according to the duration. Based on the simulation results, the ordinal regression analysis method was used to reveal the effects of the considered factors on aural comfort. The results indicate that aural discomfort sensations begin when a train runs in the middle of a tunnel but are mitigated when it approaches the tunnel exit. Furthermore, aural discomfort is positively correlated with the train speed and the distance from the driver cabin of the head car but negatively correlated with the seal index and tunnel length. As a conclusion, a mathematical prediction model was established that incorporates factors including the train speed, seal index, tunnel length and car position. It can not only forecast aural sensations under certain operation parameters and tunnel environments but also be used for determining the optimal operation parameters to ensure the best aural sensations for high-speed-train occupants. [ABSTRACT FROM AUTHOR]