Scaling of the Aeroacoustics of High-Speed Trains

Abstract

The present study focuses on the scaling of aeroacoustic sound sources of a high-speed train. To cover a wide Reynolds number range the experimental investigations are carried out with a 1:25 Inter City Express 3 model by measuring in two wind tunnels by means of microphone array technique. The facilities are the Aeroacoustic Wind tunnel (AWB) of the German Aerospace Center (DLR) in Brunswick, which provides nearly perfect acoustical conditions, and in the Cryogenic wind tunnel (DNW-KKK) of the DNW (German - Dutch wind tunnels) in Cologne, which allows measurements at higher Reynolds numbers. Two sources of sound with different characteristics are identified at Reynolds numbers up to Re = 0.46 mio. The aeroacoustic noise from the bogie section is dominant for frequencies f < 5 kHz and can be characterised by cavity mode excitation. The pantograph is the dominant source of sound above f = 5 kHz with a Aeolian tone characteristic. Additionally aeroacoustic measurements at higher Reynolds numbers of up to 3.70 mio have been conducted in the DNW-KKK. By cooling down one can increase the Reynolds number, and besides, this wind tunnel admits to vary the Mach and Reynolds numbers independently. Drawback of this facility is that it is not optimised for aeroacoustic experiments and reflexions as well as the high background noise level can disturb the results. These measurements revealed only a weak Reynolds number dependence of the noise source generated at the first bogie.