LNA model

DLR Low Noise Aircraft

The acoustic assessment of future commercial aircraft must be carried out analogously to the analysis of aerodynamic and economic effciency through simulations in the design phase of an aircraft. Even today, the sound emission of individual components, such as engines, high-lift systems and landing gears may be evaluated for various layouts and thus the quietest variant can be determined. A further reduction of the noise immission on the ground can be done conceptually only by measures that prevent the sound propagation from the sound source to the observer on the ground, that is, by the shadowing of the sound source from the observer’s point of view. For this reason, the Institute of Aerodynamics and Flow Technology is developing calculation methods to determine the noise immission on the ground for non-conventional aircraft confgurations. To verify these calculation methods, comparative wind tunnel investigations were carried out at the DLR LNA.

As part of the DLR FrEACs (Future Enhanced Aircraft Confgurations) project, DLR investigated the sound shielding properties of non-conventional aircraft confgurations. The civil aircraft concept (DLR Low Noise Aircraft, LNA) was investigated using a model sound source in the DNW-NWB. This test sound source mimics the engine noise on a model scale. The sound source is realised by focusing a pulsed laser beam onto a point. Here, the air is heated at such high temperatures that it briefly breaks down into a plasma creating a small explosion. This bang produces sound waves with an almost equal intensity in all directions. The ratio between the reference sound pressure level and the measured sound pressure level below the aircraft is the shadowing factor, which is the measure of the achieved reduction in ground noise immission.

German Aerospace Center (DLR)

Thomas Weddig · E-Mail: thomas.weddig@dlr.de · DLR.de/en