The use of Aeronautical Experimental Facilities and Measurement Techniques for the Aerodynamic Investigation of High Speed Trains

Abstract

The development of future high speed trains is driven by commercial and ecological requirements which determine the increase of speed and payload while reducing weight and improving thermal and acoustical passenger comfort. To ensure the same level of safeness then for today’s rolling stock, additional issues like Reynolds-Number and Mach-Number dependencies have to be explored. The influence of unsteady flow phenomena as well as the impact of the train’s induced flow field on humans and infrastructure has to be investigated. For this purpose, special experimental facilities and techniques originally developed for aeronautical research proved to be extremely useful. For the investigation of viscous flow effects like separation and other boundary layer phenomena, a pressurized wind tunnel can realize high Reynolds numbers without entering the compressible flow regime. Validated results for the Göttingen high pressure wind tunnel show that it is possible to use extremely small models, down to a scale of 1:100, and to get good results if the accuracy of the model manufacturing process is high enough. A second possibility to increase the Reynolds number in a wind tunnel is to cool down the working fluid, thus increasing the Reynolds number up to a factor of 5.5. The main advantage of cryogenic wind tunnels is the possibility of independent adjustment of the Mach and Reynolds number. A third possibility to increase the Reynolds number is to change the working fluid of the facility, e.g. by using water instead of air. Advanced measurement techniques, which were originally developed for aeronautical research, allow a deep insight into the physical mechanisms governing the aerodynamic performance of high speed trains. A broad variety of experimental results is presented, showing that high Reynolds number facilities are in many cases an indispensable research tool for the aerodynamics of railroad vehicles.