Investigations of Aeroacoustics of High Speed Trains in Wind Tunnels by Means of Phased Microphone Array Technique

The present study focuses on the analysis of the main aeroacoustic sound sources of a high speed train, measured in a wind tunnel. The experiments using a 1:25 Inter City Express 3 model were carried out in two different wind tunnels: The Aeroacoustic Wind tunnel (AWB) of the German Aerospace Center (DLR) in Brunswick and in the Cryogenic wind tunnel (DNW-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 advantage of this facility is its low background noise level and its nearly anechoic test section. The maximum Reynolds number, based on the wind speed and the width of the train, achieved is 0.46 million. In order to obtain higher Reynolds numbers a second measurement campaign has been conducted in the cryogenic wind tunnel, using another array for cryogenic in-flow applications. The DNW-KKK enables higher Reynolds numbers up to 3.7 million by cooling down the fluid to 100 K. The DNW-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. Differences of 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 discussed.