Analytical, Numerical and Experimental Investigation of the Tonal Sound Excitation in a Modern Low-speed Fan (de)

* Presenting author
Day / Time: 08.03.2023, 09:20-09:40
Room: Saal Y4
Typ: Regulärer Vortrag
Abstract: To reduce the noise emissions of future aircraft, a detailed understanding of the source mechanisms of fan noise is required. In order to experimentally investigate fan noise, DLR recently started to operate the new CRAFT (Co/Counter Rotating Acoustic Fan Test) rig, which is representative for urban and regional aircraft fan stages. In the noise measurements of the reference fan stage a significant difference (>10dB) is evident between the sound levels radiated upstream and downstream. To identify the acoustic effect that leads to the level difference, the tonal noise generation is evaluated analytically as well as numerically and the results are compared with the experimental data. The fan noise prediction tool PropNoise is used to provide the analytical noise prediction and the Navier-Stokes solver TRACE is used to perform Harmonic Balance simulations. The investigation shows that the phase propagation angle of the dominantly excited acoustic mode has a strong impact on the noise generation. Upstream, the mode propagation direction is almost parallel to the stator leading edge angle, whereas downstream the mode propagation direction is almost perpendicular to the stator vanes. This results in a weaker excitation of the upstream propagating mode and a stronger excitation of the downstream propagating mode.


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