Engine Development Buzzkatz Project: DLR And Rolls-Royce Reduce Aircraft Noise

As part of the Buzzkatz project, the German Aerospace Center and Rolls-Royce are working on minimizing engine noise. This is where engine concepts with a large fan diameter come into play.

Aircraft noise affects the quality of life of people living in the vicinity of airports. It is therefore necessary to reduce this for the further growth of the aviation sector. Minimizing noise directly at the source, i.e. at the aircraft engine itself, plays an important role here.

The joint research work of the German Aerospace Center (DLR) and Rolls-Royce has already made a significant contribution to reducing engine noise in recent decades. Now the new UltraFan aircraft engines from Rolls-Royce are set to reduce engine noise by up to 35 percent compared to the current generation of engines. At the same time, Rolls-Roye is aiming to reduce kerosene consumption by 20 percent for future medium-haul aircraft. In order to achieve these goals, the development of technologies and processes to reduce aircraft noise at source is particularly important.

Engine Concepts With Large Dan Diameter

The recently launched Buzzkatz project—a joint project for the acceptance of climate-friendly aviation technologies through noise reduction—focuses on further noise reduction for modern engine concepts with large fan diameters. A higher bypass ratio and the use of a high-performance gearbox can make modern engines significantly quieter. The reason is clear: a larger fan moves a larger volume of air to the rear more slowly. This means that the air does not have to be accelerated as much to generate the same thrust. This reduces the jet noise, which is mainly caused by the rapid mixing of the exhaust jet with the ambient air. At the same time, the large fan can be operated in a particularly low speed range thanks to the gearbox. Lower peripheral speeds of the fan blades also help to further reduce fan noise.

New Challenges

At the same time, this new engine architecture opens up the possibility of making the engine housing shorter and lighter. This reduces drag and helps to further reduce fuel consumption and CO₂ emissions. Acoustically, however, this creates a new challenge: a shorter intake leaves less space for sound-absorbing linings. In addition, the incoming air in front of the fan is less able to be calmed and evenly distributed. Such uneven flows at the engine inlet can cause additional fan noise. To ensure that the new architecture is actually quieter overall, this potential increase in noise from the installed engine must be precisely understood, predicted and limited by suitable measures.

Research Focus on Engine Acoustics

In order to be able to take these effects into account in engine development, the Engine Acoustics department at the DLR Institute of Propulsion Technology in Berlin is investigating them both in computer simulations and experimentally on the modular Co/Contra-Rotating Acoustic Fan Test Rig, or Craft for short. In addition, concepts for sound-absorbing engine linings are being researched on the DUCT flow acoustics test rig. High-resolution microphone arrays are used to localize and evaluate dominant noise sources.

Tests in the Acoustic Wind Tunnel And Simulations

The DLR Institute of Aerodynamics and Flow Technology in Braunschweig (Germany) complements the research on the engines. In the Aeroacoustic Wind Tunnel Braunschweig (AWB), the noise resulting from the installation of the thrust jet with the wing and a special sound propagation phenomenon with turbine sounds are investigated. The phenomenon occurs when turbine sounds pass through the highly turbulent edge of the thrust jet. The sound is scattered and distributed over many frequencies. Instead of individual clear tones, the result is a rather rushing sound that is perceived as less disturbing.

The researchers are also simulating wing shielding for the development of quieter aircraft configurations. Measurements on the DLR research aircraft HALO have successfully validated the simulation methods used. To predict cabin noise, the researchers are also investigating how engine noise propagates around the aircraft. This includes how the sound is reflected by the aircraft structure and how the turbulent flow near the fuselage changes it.

Forecasts for the Future

Aircraft noise has been regulated by international standards and binding noise limits since the 1970s. Today, modern aircraft are significantly quieter than they were just a few decades ago. According to forecasts, the targeted reduction in engine noise by 35 percent could be sufficient to compensate for the expected increase in aircraft movements by 2050 without increasing absolute noise pollution. However, this target is still below the targets set by the European Aviation Council ACARE, which is aiming for a significantly higher reduction in perceived noise emissions by 2050. Further research projects are therefore needed. (se)

Machine Authentication

Machine Operator Authentication - Why knowing "who" matters