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Partnership for Numerical Acoustic Simulation of aero-engines

Final Report Summary - PARNAS (Partnership for Numerical Acoustic Simulation of aero-engines)

=== The aircraft engine noise challenge

Despite significant technology improvements over the past twenty years, aircraft noise is still a major problem in Europe and across the world. It has to be solved by the air transport industry as a whole if current growth is to be sustained. There is a need for an economically viable, but year-on-year quieter global airline fleet to accommodate the expected traffic growth at minimal environmental cost. Already aircraft noise is limiting the capacity of a number of major airports across Europe. Airports are also failing to gain planning approval for further development because of the noise implications of future traffic growth, despite the proven demand for air travel that exists in the regions they serve. The challenge of mitigating aircraft noise has become even more acute in recent years as public and political awareness of the environmental impact of aviation on local air quality and carbon emissions has grown, particularly in Europe. This new awareness, particularly of climate change issues, means that new noise technology must be achieved without compromising fuel efficiency and carbon emissions, an additional and challenging constraint.

=== Solutions

Two major technological routes are followed to reduce aircraft engine noise: (1) increase the by-pass ratio i.e. reduce the fraction of air actually going through the combustion chamber vs. the total air getting into the engine and (2) lining the inside of the nacelle and bypass with advanced acoustic absorption materials. High and ultra-high by-pass ration engines are reaching their technological limit but have succeeded in reducing the all important jet noise contribution; they have however given a major importance to fan noise. Lining the nacelle lips, nacelle walls, bypass walls, splitters, struts and other separators is a solution to reducing fan noise. These lining materials are however expensive, complexify the nacelle and engine manufacturing process and the overall noise reduction appear to be highly dependent on the properties of the materials, the surface occupied by the material, discontinuities in the treatment and local flow velocities near the liners.

=== Computer aided design

In order to optimally design engine liners, engineers rely on computer aided design techniques to evaluate the impact of several types of treatments and to choose the best liner set-up. ACTRAN, developed by Free Field Technologies, is the world leader in acoustic computer aided design tool and ACTRAN/TM, its specialised module for aircraft engines, is used by each and every aircraft, aircraft engine and engine nacelle manufacturer in the world. Rolls-Royce is one of Free Field Technologies' early customers while the Institute of Sound and Vibration Research of the University of Southampton conducts advanced research on the topic, in partnership with both Free Field Technologies and Rolls-Royce. FFT also has a subsidiary in France working closely with Airbus; FFT being located in Louvain la Neuve (BE) also enjoys a natural and fruitful collaboration with the local university UCL.

It therefore seems quite natural to propose a joint R&D project:

- on the use of computer aided design methodologies for aircraft engine noise design
- involving UCL, ISVR, RR and FFT

=== PARNAS overview

The PARNAS IAPP project involved two SME (Free Field Technologies of Belgium and FFT France), two universities (Southampton University's Institute of Sound and Vibration Research and Université catholique de Louvain) and a large industrial company (Rolls-Royce Deutschland). All partners are working in the field of aircraft engine noise control and engine nacelle liner design and specifically in the related computer aided engineering (CAE) techniques. The project had two closely related work-packages: WP1 was dedicated to engine noise modeling and specifically to enhancing the robustness and industrial applicability of existing techniques in industrial environments while WP2 was dedicated to porting some modeling technologies (specifically discontinuous Galerkin methods) on GPU-based high-performance computing environments.

PARNAS is funded by the European Commission through the Marie Curie IAPP (Industry Academia Partnership and Pathways) mechanism. The focus of such a project is the exchange of personnel across the partners. As such:

- a fresh PhD from UCL was seconded to Free Field Technologies for 21 month to transfer his know-how on GPU-based HPC architectures
- two soon-to-be PhD were seconded to Free Field Technologies by ISVR to validate ACTRAN/DGM on selected industrial test cases provided by Rolls-Royce; they globally spent 24 month in Belgium
- a young engineer was seconded from FFT France to ISVR for 2 years to develop an engine nacelle modeling automation script and to gain some academic experience
- two engineers from Rolls-Royce spent respectively 3 month and one month at ISVR to be trained on engine noise modeling and control
- Free Field Technologies also recruited an experienced researcher for 2 years

=== Major projects outcome

The main outcomes of the project are:

For the secondees and recruitees

- an academic experience for 3 engineers from the industry
- an exposure to industrial needs and practices for three PhD from the academic world

For the companies and universities participating:

- a tighter collaboration between researchers, technology providers and industrial stakeholders in a small but strategic area (aircraft noise control)

Exploitable results are:

- more systematic methodologies to successfully use ACTRAN/TM and ACTRAN/DGM in industrial contexts
- an automated modeling script for aircraft engine noise
- a GPU-enabled version of ACTRAN/DGM making it possible to tackle problems of greater scale (large engines, higher frequencies, engine noise reflection on fuselage and wings)

The benefit for the wider community will be innovative engine nacelle designs reducing airport noise nuisance.