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Aeronautical Training Network in Aerodynamic Noise from Widebody Civil Aircraft

Final Report Summary - AEROTRANET 2 (Aeronautical Training Network in Aerodynamic Noise from Widebody Civil Aircraft)

A new Aeronautical Training Network in Aerodynamic Noise from Widebody Civil Aircraft – AeroTraNet 2 - was established in 2012. Following on from the 2006-2010 AeroTraNet programme, AeroTraNet 2 provided between 2012 and 2016 integrated cross-European training, extending the quality of the postgraduate research training offer for Early Stage Researchers and Established Researchers, with strong links to the European aeronautical and power generation industry. AeroTraNet 2 brought together the complementary expertise of five established European academic institutions, two multi-national aerospace and power generation companies, one Small Medium Enterprise (SME), and one national research centre to offer structured, flexible, well-integrated, a la carte, doctoral and post-doctoral training experiences for the new generation of European aerodynamicists and noise specialists.

The five academic partners and the SME joined their competences and research training resources towards the common objective of modelling the broad-band shock cell noise radiation towards the cabin of a wide-body civil aircraft, based on an aircraft engine dual-flux jet configuration from the private sector Associated Partner Airbus SAS. The University of Leicester performed shock-tolerant Detached Eddy Simulations of the under-expanded jets, the Centre Européen de Recherche et de Formation Avancée en Calcul Scientifique (CERFACS) provided Large Eddy Simulations of turbulent jets with weak shocks, the Università degli Studi Roma Tre supplied advanced flow-noise correlations, the Von Karman Institute (VKI) generated a bespoke validation database from a purpose-built new jet noise experimental rig, the Institut National Polytechnique de Toulouse (INP) contributed with a sensitivity analysis on the jet plume dynamics, and the Istituto Nazionale per Studi ed Esperienze di Architettura Navale (CNR INSEAN) supported the development of the instrumentation at a smaller scale test rig at Università degli Studi Roma Tre. Formal methods for evaluating the uncertainty in the predictions and measurements performed by the project participants using such a broad range of tools were developed and implemented by the University of Greenwich. The analysis was developed in close collaboration with industrial Partner Alstom UK Ltd, who joined the General Electric (GE) group as GE Power during the programme. Alstom UK Ltd also provided a review of the knowledge management and knowledge capture tools available, investigating their applicability to knowledge capture the output of the AeroTraNet 2 programme.

The network recruited 11 Early Stage Researchers (ESRs) and one Established Researcher (ER) between 2012 and 2016, 10 of whom were from European countries. The ESRs and the ER benefited from the synergies in the training activities and facilities available through this FP7 Marie Curie Integrated Training Network (ITN), as well as from the trans-national mobility that enhanced their personal development as active Europeans in an inclusive European Community. The Associated Partner Airbus SAS provided a common dual-flux jet configuration and engine operating line as a common target for all ESRs to work towards. This represented the forthcoming generation of turbofan engines for civil transport, featuring an increased by-pass ratio and a staggered nozzle geometry. The programme of computationally intensive Large Eddy Simulations (LES) at CERFACS resolved the flow and near-field pressure unsteadiness in great detail. This has generated a database that was interrogated for velocity-pressure coupling in the near-field, as well as for testing the approximation level of less computationally expensive methods. This result was achieved through concurrent significant advances in the LES code, by implementing shock-tolerant algorithms compatible with the high-order solver. An important contribution came from the interaction among the numerical ESRs, in particular between France and the United Kingdom (UK). The less computationally demanding Detached Eddy Simulation, using a lower-order solver, was found to be able to reproduce enough of the flow dynamics to deliver with appreciable engineering accuracy the characteristic near-field component of broad-band shock-associated noise. The timescales of this computationally lighter method are sufficient for considering this tool in the design timescale of the industrial associate partner.

A further area of successful international collaboration brought about by this network is in the development of a community-based computational fluid dynamics post-processor. This activity used the software platform Antares, from CERFACS, which CERFACS has made available as a royalty-free software subject to copyright. The development of a Ffowcs Williams and Hawkings acoustic analogy post-processor for projecting noise from the vicinity of a sound source to further afield was coordinated between the Coordinator at the University of Leicester, UK, and CERFACS, in France, as a development of Antares. This activity benefited from the external collaboration of Onera, France, as well as from the oversight of Airbus SAS. Joint code validation and testing has strengthened the confidence in this post-processor which, in the spirit of open research, CERFACS has made accessible to the wider research community. The testing included a sensitivity study on the proximity of the source to the Ffowcs Williams and Hawkings integration surface and on the topological sharpness of the surface edges. New insight has been generated in the application of numerical integration and differentiation procedures to this problem as well as more practical guidelines on how to use the software for producing predictions within engineering accuracy. A new module for the convective form of the Ffowcs Williams and Hawkings acoustic analogy was coded at Leicester and ported at CERFACS, specifically for studying jets from turbofan engines at cruise conditions.

AeroTraNet 2 has fostered significant methodological, instrumentation, and technological development across Europe. Joint beneficiaries of this outcome have been VKI, in Belgium, the Università degli Studi Roma Tre and CNR INSEAN, in Italy. VKI and the Belgian government made significant capital investments in the experimental activity of AeroTraNet 2, which produced a dedicated new facility for testing dual-flux jets in the absence of co-flow. The design, commissioning, and testing of the facility was aided by mutual secondments at VKI, Roma Tre, and CNR INSEAN. The exchanges promoted the transfer of knowledge among the experimentalists and the addition of new experimental techniques to the repertoire of VKI, specifically Background Oriented Schlieren photography. This technique enabled the assessments of the oscillating shock train in the dual-flux jet when it was operated over-expanded. Pressure-density gradient correlations have shown the causality between jet shear-layer events and the pseudo-sound recorded outside the jet shear-layer. By a wavelet decomposition technique, the radiating component of the pressure fluctuation that contributes directly to the aircraft cabin noise was decoupled from the non-radiating pressure component.

The University of Greenwich, in collaboration with Alstom UK, developed a framework evaluating the uncertainty in the knowledge generated by the AeroTraNet 2 research activities. Process mapping was used together with a metric system to identify and exploit opportunities for strengthening the conclusions from individual research activities through complementary validation tests as well as through a joint analysis of the results. A systematic technique for evaluating the uncertainties in the chain of tools used for predicting the flow and noise was designed and tested around the network.

By combining their well-established doctoral training schools and graduate training programmes, the academic and industrial partners have trained a well-integrated team of 11 ESRs and 1 ER. By the end of the project, these researchers learnt to combine their different research techniques to push forward the state of the art of shock cell noise prediction applied to aircraft design. This is a significant progress in structuring the European research training capacity in aerodynamics, noise, and knowledge capturing, to support the European knowledge based economy.

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