The double-model measurements have been carried out in the cryogenic wind tunnel DNW-KKK in Cologne. This wind tunnel is a Göttingen-type wind tunnel with closed test section with the dimensions 2.4×2.4 m. The Mach number can be varied between 0.10 < Ma < 0.30 and the Reynolds numbers is adjusted by varying the fluid temperature. The DNW-KKK uses nitrogen as working fluid which can be cooled to temperatures as low as 100 Kelvin, leading to Reynolds numbers of up to profiles disclose a underfloor flow of the train model, which is comparable to the one of a full-scale train moving over the ground. To consider the influence of the temperature on observed amplitudes, the relations for the density and the speed of sound in Curle's equation were assumed to be valid for the present sound source. As a consequence, the sound pressure levels are found to be temperature independent, since the data are discussed in terms of the Mach number. For the temperature dependent scaling of the frequencies, a dimensionless frequency ζ is introduced, which assumes a linear relation between the frequencies and the speed of sound, implying a correlation between the wavelength and a typical length of the sound emitting cavity. The experiments disclose, that ζ is an appropriate nondimensional parameter to describe the characteristics of the considered sound source at different temperatures. The investigations of the Reynolds number influence reveal a significant influence on tones in the spectra of up to ± 9 dB, whereas the influence on broadband noise is less than ± 3 dB. The sound emitted by the bogie with mounted fairing contains more tonal components of lower amplitude, and again these peaks are significantly decreased for the higher Reynolds number. The powerlaw exponent α = 6 according Curle's equation cannot be found for all investigated Mach numbers. The influence of the Mach numbers on the sound pressures show a significant inconsistency, and furthermore this behaviour differs for the two investigated configurations.
Aeroacoustics of a high-speed train double model at high Reynolds numbers
2012
15 Seiten, 8 Bilder, 28 Quellen
Aufsatz (Konferenz)
Datenträger
Englisch
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