Alexander Orellano

Cross-wind effects on road and rail vehicles

This paper presents a review of recent research that has been carried out on the cross-wind effects on road and rail vehicles. After a brief introduction to the issues involved, the risk analysis framework is set out. All risk analysis methods require some knowledge of cross-wind aerodynamic force and moment coefficients, and methods of obtaining these through full scale and wind tunnel testing and through Computational Fluid Dynamics methods are then described. The picture of the flow fields around vehicles that is suggested by these measurements and calculations is then presented, and the steady and the unsteady aerodynamic force characteristics described. The detailed methodology for using this information to predict accident risk is then set out, including details of the vehicle dynamics system models that can be used. Finally potential alleviation methods are described and suggestions made for further works.

Analysis of Flow Structures in the Wake of a High-Speed Train

Slipstream is the flow that a train pulls along due to the viscosity of the fluid. In real life applications, the effect of the slipstream flow is a safety concern for people on platform, trackside workers and objects on platforms such as baggage carts and pushchairs. The most important region for slipstream of high-speed passanger trains is the near wake, in which the flow is fully turbulent with a broad range of length and time scales. In this work, the flow around the Aerodynamic Train Model (ATM) is simulated using Detached Eddy Simulation (DES) to model the turbulence. Different grids are used in order to prove grid converged results. In order to compare with the results of experimental work performed at DLR on the ATM, where a trip wire was attached to the model, it turned out to be necessary to model this wire to have comparable results. An attempt to model the effect of the trip wire via volume forces improved the results but we were not successful at reproducing the full velocity profiles. The flow is analyzed by computing the POD and Koopman modes. The structures in the flow are found to be associated with two counter rotating vortices. A strong connection between pairs of modes is found, which is related to the propagation of flow structures for the POD modes. Koopman modes and POD modes are similar in the spatial structure and similarities in frequencies of the time evolution of the structures are also found.

Aerodynamic Improvements and Associated Energy Demand Reduction of Trains

The importance for developing energy efficient rail vehicles is increasing with rising energy prices and the vital necessity to reduce the CO2production to slow down the climate change. This study shows a comparison of different train types like regional and high-speed trains and provides estimation for improvements of the aerodynamic drag coefficient. Out of this estimation an assessment ofthe associated energy reduction is shown taking into account typical operational cycles with acceleration, constant speed and deceleration phases. Traditionally, aerodynamic improvements of high-speed trains were in the focus of the engineering community as the resistance to motion is increasing with the square of the velocity. However, this study reveals that it is necessary to consider regional and commuter applications equally. This transport sector is not only the one with the highest share in the market but exhibits also much higher potential for aerodynamic improvements then present day already optimized high-speed trains.