BRAUNSCHWEIG, Germany - The German Aerospace Center (DLR) has announced that they are now analyzing some 400 gigabytes of microphone data following wind tunnel tests to study how engine placement and porous materials may impact noise levels.
At DLR's acoustic wind tunnel (AWT) in Braunschweig, Germany, the agency studied a pair of concepts, one of which is a traditional configuration where the jet engine is placed below the wing, which is typical of commercial airliners. In addition, DLR studied the configuration in which many business jets use, which places the engine at the tail of the aircraft.
For the latter, they set up several different test series. "We measured three different tail units acoustically on the business jet," explains Jente. "Two conventional tailplanes in a cross and T arrangement, as well as a U-tailplane, in which the horizontal stabilizer should shade the engine noise." The researchers' goal here was to evaluate the acoustic advantages and disadvantages of different configurations.
For this purpose, researchers from the DLR Institute of Propulsion Technology set up two linear microphone arrays, more than three meters long, in the AWB, i.e. an arrangement of microphones, from which the precise positions and the direction-dependent intensities of the sound sources on the engine nozzle, fuselage and wing are calculated became. In addition to the linear microphone arrays, far-field microphones on the ceiling measured the sound radiation in different directions, since this can vary greatly with the different elevator concepts.
In their wind tunnel construction for the commercial aircraft, the researchers carried out another experiment: they chose a porous material for the landing flaps. DLR has already demonstrated in other tests that porous materials have positive acoustic properties. When flowing over porous materials, pressure fluctuations in the turbulent boundary layer are reduced, which are then no longer converted into sound at the trailing edge of the landing flap.
The two DLR institutes are now evaluating 400 gigabytes of microphone data. The results help to develop technologies that can reduce the aircraft noise level of future aircraft. The researchers have prepared the measurements in detail for years with numerous project participants.
