This paper describes the results of experimental work to determine the structure of the slipstream and wake of a high speed train. The experiments were carried out using a 1/25th scale model of a four-coach train on a moving model rig (MMR). Flow velocities were measured using a rake of single hot films positioned close to the model side or roof. Tests were carried out at different model speeds, with and without the simulation of a crosswind. Velocity time histories for each configuration were obtained from ensemble averages of the results of a number of runs. A small number of particle imaging velocimetry (PIV) experiments were also carried out, and a wavelet analysis revealed details of the unsteady flow structure around the vehicle. It was shown that the flowfield around the vehicle could be divided into a number of different regions of distinct flow characteristics: an upstream region, a nose region, a boundary layer region, a near wake region and a far wake region. If the results were suitably normalized, the effect of model speed was small. The effect of crosswinds was to add an increment to the slipstream and wake velocities, and this resulted in very high slipstream velocities in the nose region.
Recent experience with the operation of high-speed railways in the UK and elsewhere has revealed the phenomenon, termed 'ballast flight', of ballast particles becoming airborne during the passage of trains, potentially causing damage to both the railhead and the vehicle. This article reports the results of an investigation into the mechanical and aerodynamic forces acting on ballast particles that are generated during the passage of a high-speed train and addresses the question whether these might offer a possible explanation for the initiation of ballast flight. As the high-speed trains passed, measurements were made of the air pressure and velocity at various locations across the track, and of the velocity and acceleration of the track system (sleeper and rails) and the ballast itself. The aerodynamic forces exerted on a suspended ballast particle were also measured. An analytical model of the behaviour of small ballast particles was constructed to assist in the interpretation of the measured data. Analysis of the data and modelling suggest that neither mechanical forces nor aerodynamic forces in isolation are likely to be sufficient to initiate ballast flight under the conditions investigated, but that the phenomenon could arise from a combination of the two effects. It appears that the process is stochastic in nature: further work, with an increased number of measurements, is required to explore this.
Extreme high temperatures are associated with increased incidences of rail buckles. Climate change is predicted to alter the temperature profile in the United Kingdom with extreme high temperatures becoming an increasingly frequent occurrence. The result is that the number of buckles, and therefore delays, expected per year will increase if the track is maintained to the current standard. This paper uses a combination of analogue techniques and a weather generator to quantify the increase in the number of buckles and rail related delays in the south-east of the United Kingdom. The paper concludes by assigning a cost to the resultant rise in delays and damage before making recommendations on how these effects can be mitigated.
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