Analysis On Ground Effects Of High-Speed Trains And The Resultant Fatigue Damage To The Equipment Bay

As a large, long-shaped object running close to the ground, trains are heavily influenced by the so-called’ground effect’, which increases in prominence with higher speeds. Constrained in the narrow space between the train and the ground, the air flow underneath a train is heavily influenced by the operation conditions and shows very complicated characteristics and variations. The aerodynamic loads upon the train also increase with higher speeds. This not only limits the operational speed, ride comfort and running stability, but also causes impact and fatigue damage to the rail and train structures, further endangering operational safety.This paper firstly analyzes the performance of different computational methods for modelling the aerodynamics around a train, as well as the influences of the blockage ratio and Reynolds number on different aerodynamic parameters. Based on these results, numerical models are established of a single train running in the open air and through a tunnel, and additionally, of two trains passing by each other in open air. These models are then applied to analyze the aerodynamic loads, flow structure and the surface pressure distribution on the train. The aerodynamic load spectra are then compiled for the equipment bay and the fatigue damage on the apron caused by the aerodynamic load is thus evaluated. The main research work is summarized as follows:1. RANS and LES are adapted to simulate the air flow around the train. Steady and unsteady results of the train drag force, surface pressure distribution and wake structure are analyzed comparatively to study the performance of the two methods in simulating air flow around trains. By evaluating the accuracy and computational cost, DDES, which combines the RANS and LES is chosen to carry out subsequent research.2. Train simulation models of different blockage ratios and Reynolds numbers are established to investigate the influence of the two factors on a range of aerodynamic parameters. The results indicate that their influences on different aerodynamic parameters differ greatly, which provides justification to choose appropriate blockage ratio and Reynolds numbers for wind tunnel and computational simulation.3. To investigate the ground effect phenomenon,3-dimensional transient DDES is adapted together with a sliding mesh technique, to establish numerical models of a single train running in open air and through a tunnel, and for two trains in a passing event in open air. Through thorough analysis of the data, the characteristics and variations of aerodynamic forces, velocity and pressure fields are gained in both time and frequency domains. The results show that the aerodynamic characteristics in the tunnel operation and passing event are far more complicated than under the open air condition scenario. The influences of the head profile and train length on the aerodynamic parameters are also studied, allowing for a comprehensive picture of the air flow mechanisms around the train.4. Surface pressure distributions on the train in different operational scenarios are analyzed to identify the critical locations of stress on the equipment bay structure. The characteristics of these aerodynamic loads are investigated in both time and frequency domains. The load spectra of different operational scenarios are compiled by the rain flow counting method to gain the "sample" aerodynamic load spectra, which is used in subsequent investigations.5. The Finite Element Method is applied to analyze the strength of the apron. The critical locations of fatigue damage and the load-stress transfer factors are identified by the quasi-static method. Stress spectra of the critical locations are derived from the "sample" aerodynamic loads obtained earlier according to the load transfer factors. These are then extended according to the Wuhan-Guangzhou high speed line operation conditions, to get the cumulative damage on the apron based on the Miner’s law. The results indicate that the aerodynamic loads will not cause apron failure within its standard operational life time.