Methodology

A further significant reduction of aircraft noise per operation is only achievable with major design changes and disruptive aircraft concepts and noise reduction technologies beyond the proven noise reduction means of today’s aircrafts and demonstrators. 

ARTEM therefore chose the following major aspects of future aircrafts and related noise reduction technologies:

• The radiation of noise towards the ground shall be prevented to the best possible extent.

  This includes the effective damping and absorption of noise on all surfaces of the aircraft capable to carry those devices. Furthermore, the shielding capabilities of the aircraft structure should be used to the best possible extent.

• The noise originating from the interaction between different airframe components and between engines and airframe must be well understood in order to avoid them by optimized design, or apply noise reduction means which might be already available. A reduction at the source will be most valuable.

Liners for low frequencies and broad-band attenuation

Future aircrafts will rely – at least in part – on air breathing turbofan engines with a BPR increased to 16 and beyond. In order to reduce the associated weight and drag penalty of these large engines, the nacelles will be shorter and a reduced amount of space will be available for the installation of liners. At the same time, the noise characteristic will be shifted even more from tonal noise towards broad band noise and due to the large dimensions of the engine and blades also to low-frequency broad band noise. Therefore, novel liner concepts will be required for the efficient damping of low-frequency broad band noise for the installation in confined environments. This topic applies to mid-term tube-wing aircraft configurations to the same extent as to more long-term future concepts including blended-wing-body aircraft configurations.

A new dimension of interaction effects

When looking at these future configurations it becomes clear, that interaction effects between airframe components and the interaction between propulsion system and the airframe, will be present as well - however differing significantly depending on the configuration. E.g. for embedded engines, the effect of boundary layer ingestion needs to be considered – as benefit for the aerodynamics and as challenge for the fan inflow conditions in terms of loads, performance, and noise.

 

The project structure resembles the main topics of ARTEM: Reduction Technologies and the configuration analysis

 

Embedding novel noise reduction technologies in future aircrafts

The ambitious target in ARTEM consists of providing detailed configurations for a tube-and-wing configuration with semi-buried engines (building on the NOVA concept of ONERA) as a representation of a possible 2035 configurations

A possible candidate for 2035 air transport: ONERAs NOVA concept with semi-buried engines (© ONERA, 2015)

as well as two blended-wing configurations anticipated for 2050 for short (REBEL) and long range (BOLT). The detailed analysis includes the characterization of the main noise sources of these aircrafts, in order to identify the low noise technologies most appropriate for the noise reduction.

Finally, the new concepts will be assessed with the technologies needed for the best noise reduction.

The noise impact will be evaluated for a single aircraft, but also at fleet and airport level, considering not only a conventional scenario as reference one but also scenarios including the most-suitable trajectories for the novel configurations.

The noise sources at the aircraft, the flight trajectories, and the propagation through the atmosphere are taken into account for the noise prediction to the ground (© Lothar Bertsch, DLR, 2017).

 

A non-metrics based approach will complement the technical assessment: an auralization and subsequent listening study with voluntary participants reveals a psycho-acoustic judgement in terms of annoyance of conventional and novel configurations.

The auralization lab of Empa will allow voluntary participants to listen to the novel aircrafts fly-by (© Empa, 2017).

So ARTEM finally allows listening to the pass-by of the aircraft of the future already today.