Slat noise measurements in open-jet, hard-wall and hybrid wind tunnel test sections

• Published in: Journal of sound and vibration 2023-03, Vol.546, p.117420, Article 117420
• Main Authors: Sanders, M.P.J., Venner, C.H., de Santana, L.D.
• Format: Article
• Language: English
• Subjects: 30P30N; Aeroacoustics; Comparability; Experimental study; High-lift device; Microphone array
• ISSN: 0022-460X; 1095-8568
• DOI: 10.1016/j.jsv.2022.117420

This paper assesses the comparability of aeroacoustic slat noise measurement in an open-jet, a hard-wall, and a hybrid test section configuration. The 30P30N common research model was tested in the Aeroacoustic Wind Tunnel of the University of Twente at a chord-based Reynolds number up to 1⋅106 and free-stream Mach number 0.15. Pressure distribution measurements were used to determine the aerodynamic similar condition of the flow in the slat cove. These conditions are subsequently validated by time-averaged 2D PIV measurements. The experiments show that general aspects of the flow in the slat cove are similar when the Cp distribution around the leading-edge slat element in each test section configuration is comparable. Overall, the shear layer path and reattachment point are in close agreement, showing that the aeroacoustic noise production mechanisms are comparable. Microphone phased array measurements were subsequently conducted to compare the far-field noise characteristics originating from the slat in each test section configuration. A framework is proposed to correct the acoustic measurements of each test section configuration to a standard free-field condition. Transmission loss corrections are required for the microphone measurements in the hard-wall and hybrid test section configurations, whereas a coherence loss model was validated and applied to correct the microphone measurements in the open-jet. The measured noise spectra in each test section configuration show differences up to approximately 5 dB. In general the differences were found to be smaller. The largest differences are seen for small angles of attack with noise levels in the open-jet test section showing considerably higher values than the hard-wall test section and hybrid test section results. In addition, the behavior of the vortex shedding hump in the high frequency range is different in the open-jet measurements, which could be related to the larger noise level differences at small angles of attack. •Slat-noise measurements performed in different test section configurations are comparable.•The global flow fields in the slat cove are comparable in each test section configuration.•Measured far-field noise levels show a maximum difference of 5 dB but are in general lower.•Coherence loss effects have to be taken into account in the open-jet test section.•The vortex shedding noise mechanisms behaves differently in the open-jet test section.