Methodology For Air-conditioning System Design of the Interior Airflow Field in Compartments of High-speed Trains

Abstract

The air-induced transient pressure and thermal environment in the compartment of high-speed trains (HSTs) depend on regulating the air-conditioning system. However, the train operation scenarios are complex and changeable, and the air-conditioning system is prone to mismatch with the external environment, which in turn causes excessive air pressure fluctuations, poor thermal environment, high CO₂ concentration and other problems that endanger the passengers’ travel comfort and safety. In this regard, this dissertation utilized field questionnaire surveys, on-site measurements, numerical simulations, and proper orthogonal decomposition (POD) methods to research air-conditioning system design methods of HSTs oriented to the interior airflow field environment of compartments. It aims to provide scientific guidance for ensuring passenger pressure/thermal comfort and improving the air quality in HSTs. The main work of this doctoral thesis is as follows:

Subjective questionnaire surveys and flow field measurement experiments were carried out in operating HST compartments. A new evaluation index, pressure intensity (PI), which considers several pressure fluctuation parameters, including pressure change amplitude, effect frequency and effect time, was proposed. Then, a mapping relationship between this index and the pressure comfort evaluation scores was established to evaluate the pressure comfort of passengers in HSTs comprehensively. Meanwhile, the influence of thermal environment parameters for HST compartments on the subjective thermal comfort evaluation was explored, and the passengers’ thermal neutral temperature and thermal preference temperature were determined. The existing thermal comfort evaluation model was modified based on actual thermal sensation voting, and its prediction accuracy was improved by approximately 75% compared to the existing model.

A numerical calculation method for HST internal and external pressure transfer based on a high-static-pressure fan model was developed. An equivalent model of the high-static-pressure fan using the porous media model was proposed, and the parameters, including the numerical model, computational meshes, and solution settings covering the high-static-pressure fan module, were determined. The accuracy of the numerical method for HST internal and external pressure transmission was verified by field test data. Additionally, the numerical method of the thermal environment in HST compartments was determined. The boundary condition setting, meshing strategy and solution setting scheme of the numerical model were clarified, and the accuracy of the thermal environment simulation method in HSTs was validated by conducting on-site measurements.

A collaborative control scheme for pressure comfort and CO₂ concentration was proposed. The airtightness performance of HSTs with active/passive pressure protection devices was evaluated, the relationship between the pressure comfort and the dynamic sealing index (τ_dyn) at different sections was explored, and the influencing mechanism of the time-course change of CO₂ concentration in compartments under the active/passive devices was revealed. The results show that the pressure comfort score demonstrates an exponential decay relationship with the increase of τ_dyn ; the CO₂ concentration in compartments has a positive linear correlation with the passenger volume, but a power exponential negative correlation with the fresh air volume. The proposed active/passive pressure protection device combined with the control scheme is capable of making the interior pressure comfort equivalent to that of the existing active device under its τ_dyn increasing by about 20 s; at the same time, the maximum CO₂ concentration in the compartment can decrease by nearly 3000 ppm compared with the current passive device.

An improved POD reconstruction method integrating the radial basis function (RBF) model and orthogonal experimental design was established to complete the rapid design of the thermal environment in HST compartments. The orthogonal experimental design significantly reduced the sample size required for the preliminary numerical simulation. The embedded RBF model was adopted to construct the mapping relationship between the orthogonal basis coefficients of multidimensional scattered data and the design parameters. Then, the numerical simulation method verified by the experiment was implemented to validate the accuracy of the proposed improved POD method. The results indicate that the average R² between the reconstructed and numerical results of each evaluation index for all test cases exceeds 0.97. Given that, the single optimal and comprehensive optimal ventilation parameter values for the internal thermal environment were determined, considering the modified thermal comfort prediction model, draft sensation, and air age as key evaluation indices.

Date of Award	18 Dec 2025
Original language	English
Awarding Institution	City University of Hong Kong
Supervisor	John Z LIN (Supervisor) & Tiantian Wang (External Supervisor)