Investigations of aeroacoustics of high speed trains in wind tunnels by means of the phased microphone array technique

Abstract

The present study evaluates the capabilities of the acoustic phased array technique for the localization and quantification of aeroacoustic sound sources of a high speed train in wind tunnels. The experiments using a 1:25 ICE 3 model were carried out in two different wind tunnels: The Aeroacoustic Wind tunnel of the German Aerospace Center (DLR) Brunswick (AWB) and in the Cryogenic wind tunnel (KKK) of the DNW (German – Dutch wind tunnels) in Cologne. The AWB is a Goettingen – type wind tunnel with open test section which is surrounded by an anechoic chamber. The microphone array consists of 143 microphones and is positioned outside the flow. In order to achieve reasonable results a shear layer correction is applied. Performing a phase-calibration can increase the signal-to-noise ratio, especially for higher frequencies. The maximum Reynolds number, based in the wind speed and the width of the train, achieved is 0.5 million. In order to obtain higher Reynolds numbers a second measurement campaign has been conducted in the cryogenic wind tunnel, using another array with 144 microphones for cryogenic in-flow applications. The KKK enables higher Reynolds numbers up to 4 million by cooling down the fluid to 100 Kelvin. The KKK has a closed test section and the microphone array is mounted on a side wall inside the wind tunnel, and therefore the measurements are affected by the turbulent boundary layer. Drawback of this facility is that it is not optimized for aeroacoustic experiments and reflexions as well as the high background noise level can disturb the results. Influences between the two different experimental setups on the results and primarily, influence of the Reynolds number on the aeroacoustic of a high speed train will be presented and discussed at the conference.