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TurboNoiseBB

TurboNoiseBB (Validation of improved turbomachinery noise prediction models and development of novel design methods for fan stages with reduced broadband noise) is a 3,5-year research project aiming to deliver reliable prediction methodologies and noise reduction technologies in order to allow European Aerospace industries to design low-noise aircraft to meet society’s needs for more environmentally friendly air transport and to win global leadership for European aeronautics with a competitive supply chain.

The project is focusing on fan broadband (BB) noise sources and will offer the possibility to acquire an experimental database mandatory to validate the Computational Fluid Dynamics and Aero Acoustic (CAA) simulations from the sound sources to the radiation from aircraft engines.

Fan Test rig UFFA at Anecom AeroTest in Wildau, Germany. The fan tests in the project were conducted in March 2018.

Background

In recent years, the steady growth of the air traffic amount has increased the sensitivity and the concerns of airports neighbouring communities with respect to local environmental issues. While global environmental issues such as climate change and emission of greenhouse gases have recently driven the political and research agendas, noise has remained one of the most significant factors of limitation for air transport growth in Europe. Airports are struggling to gain planning approval for further developments because of the noise implications of future traffic growth, despite the proven demand for air travel that exists in the regions they serve.

The Advisory Council for Aeronautics Research in Europe (ACARE) has successively developed the Strategic Research Agenda (SRA – 2002) and Strategic Research and Innovation Agenda (SRIA - 2012) which focus on specific “challenges” including “Noise and Emissions”. The SRIA provides goals to be achieved beyond 2025, calling for the emergence of “Generation 3” noise reduction solutions such as UHBR powerplant system multi-disciplinary optimisation through Advanced Source Modelling and Applications, aimed at reducing perceived noise by 65% in 2050 relative to the year 2000.

The continuous increase of the bypass ratios of modern aeroengines has led to a new generation of ultra-high-bypass-ratio turbofans (UHBR) with lower-speed fans and has had by design a significant impact reducing jet noise. In addressing the noise goals set by the SRA (2002) for 2020, the previous research efforts aimed at so-called generation 1 and 2 solutions have also been successful in reducing fan tonal noise.

Today’s vision of a UHBR engine drastically differs from current turbofan engines by an increased By-Pass Ratio (BPR) from 12 to 16-20, an even lower fan tip speed, and a shorter intake and exhaust duct. The noise signature of such an engine is highly dominated by fan noise and this trend will even grow for the future UHBR engines. As an example of the increased noise floor represented by broadband noise on future engine concepts, a quantitative assessment on a generic aircraft platform showed that if all tonal components were removed from the total engine noise spectrum, the resulting EPNL (Effective Perceived Noise Level) at approach would be reduced by 2.2 EPNdB for a turbofan engine with BPR (bypass ratio) 5 and by only 1.5 EPNdB for a geared fan engine with an extremely high BPR of 16. Indeed, the noise generated by the fan system is responsible for 50 to 65% of the aircraft noise for all certification conditions. And the broadband part of that contribution is currently estimated to about 80-90% in approach and about 40% at takeoff. So the reduction of fan broadband noise has the maximum effect on noise reduction for modern aeroengines.

Noise source breakdown of a typical large commercial aircraft with BPR10 engine  (picture source: Airbus)

While the need to reduce tonal noise will remain, simultaneously reducing fan broadband noise is definitely a major challenge to address in order to further reduce noise of ultra-high-bypass-ratio ducted turbofans.