Microphone Array Wind Tunnel Measurements of Reynolds Number Effects in High-Speed Train Aeroacoustics

Abstract

The present study focuses on the Reynolds number dependence of high-speed train aeroacoustic sound sources. To cover a wide range of Reynolds numbers the experimental investigations are carried out on a 1: 25 scale-model of the high-speed train Inter City Express 3 by conducting microphone array measurements in two wind tunnels. The latter are the Aeroacoustic Wind tunnel (AWB) of the German Aerospace Center (DLR) in Brunswick, providing nearly perfect acoustical conditions, and the Cryogenic wind tunnel (DNW-KKK) of the DNW (German -Dutch wind tunnels) in Cologne, allowing measurements at higher Reynolds numbers. Two types of sound sources with different characteristics at Reynolds numbers of up to Re = 0.46 × 106 have been identified by measurements in the AWB. It was found, that the aeroacoustic noise from the bogie section is dominant for frequencies f < 5 kHz and can be characterised by cavity mode excitation. Further, the pantograph is the dominant sound source above f = 5 kHz with an Aeolian tone characteristic. Additional aeroacoustic measurements have been conducted in the cryogenic wind tunnel DNW-KKK in order to analyse the Reynolds number dependence of the noise generated at the first bogie, for higher Reynolds numbers of up to Re = 3.70 × 106. The DNW-KKK admits varying the Mach and Reynolds numbers independently. These measurements reveal only a weak Reynolds number dependence of the noise source generated at the first bogie.