THE CHALLENGE OF SLAT NOISE REDUCTION BY RETRO-FIT TECHNOLOGY

Abstract

Within the EU co-funded research project Inventor efforts were driven to design and test so called slat cove liners based on porous material. The selected materials were off shelf open cell structures and ALM-based porous media. Acoustic tests were achieved with two basic configurations three different wind tunnels. First, a noise reduction was achieved for the Bristol type inserts in all wind tunnels as shown for UoB and AWB. Second, the TE-inserts showed on the one hand noise reductions up to 3 dB but on the other hand the obtained data show contradicting results for selected test cases. This is shown by the data presented. Banded OASPL data as derived from the F2 measurements e.g. for the Kelvin 2 trailing edge modification showed a noise reduction in F2 but a noise increase in AWB. The latter led to the assumption that not at least installation issues may deteriorate the flow and thus diminish the achieved noise reduction. The current work will emphasize the acoustic achievements, including the final application of porous treatments on a real 3-dimensional high lift wing as can be seen here by the comparison of sound pressure level spectra from the respective measurements in DNW-NWB. Furthermore, next steps in order to improve this technology are proposed.