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Support to Future CROR and UHBR Propulsion System Maturation

Periodic Reporting for period 3 - PropMat (Support to Future CROR and UHBR Propulsion System Maturation)

Reporting period: 2019-01-01 to 2020-06-30

Novel engine technology can deliver a step change in the reduction of fuel consumption and noise. The development of innovative propulsion concepts and their integration in large transport aircraft is therefore a key contributor to achieve the environmental targets for aviation as set in FlightPath2050.

The leading European aircraft and aero-engine industry proceeds in Clean Sky 2 with the development of candidate low fuel burn propulsion concepts following both evolutionary and more revolutionary paths:
• The Ultra High Bypass Ratio turbofan (UHBR)
• The Open-Rotor
Numerical analysis and wind tunnel test campaigns are indispensable for the development of future aircraft that will be designed specifically around such novel propulsion systems, including the preparation of flight test.

Focused towards these Clean Sky 2 activities, the overall PropMat project objective is to make a distinctive contribution to the technology maturation of the novel propulsion concepts with:
• Innovative numerical and experimental methods and tools as needed for aerodynamic &-acoustic characterisation,
• Analyses and experimental results for the novel propulsion concepts for large transport aircraft (aircraft concepts, wind tunnel models, flight demonstrators and/or product aircraft)
Firstly, PropMat investigated an innovative chase aircraft acoustic in-flight measurement methodology through an experimental test campaign in which NLR’s Citation aircraft has been measuring the noise of a propeller aircraft. The feasibility was demonstrated of providing accurate acoustic in-flight measurements in all directions and at various distances from the flying demonstrator of an innovative engine configuration, in various operational conditions.

Secondly, methods for acoustic measurements in wind tunnel have been improved. A data processing method has been developed to separate tones and broadband noise in wind tunnel experimental acoustic data for a CROR configuration . The method has been validated on multiple data sets from two different wind tunnel tests. In addition, a method has been developed and verified to assess the acoustic modes in the inlet of a UHBR with a sensor array, including guidelines for its design.

Thirdly, the possibilities to design and manufacture scaled acoustic liners for wind tunnel models have been investigated. First a design approach for geometrically scaled liners has been developed, taking into account performance requirements, manufacturing, and testing constraints. The design approach was verified on eight samples. For further improvement, parameters of the scaled liners have been tuned.

Fourthly, wind tunnel experimental data in the DNW-LLF data base for the CROR configuration from Clean Sky 1 were extrapolated. Numerical extrapolation techniques were validated with the DNW-LLF experimental data. Next the DNW-LLF experimental data base was extrapolated to higher Mach numbers for representativeness at aircraft take-off.

Fifthly, design and advanced finite element modelling methods were developed to extend the aeroshape of the fan blade at wind tunnel scale with foot and fixation and to define the internal structure of the full composite fan blade, including ply lay-up and orientation, for accurate manufacturing. Design and modelling methods were verified on coupon and element levels. Methods were initially verified against the fan blade aeroshape from the EU ASPIRE project and later applied on the initial aeroshape for the fan blades for an UHBR wind tunnel test, as a contribution to the fan blade Preliminary Design Review in LPA.
Progress beyond state of the art

For acoustic in-flight measurements the state of the art is to assess the take-off and approach acoustic characteristics of an aircraft using ground instrumentation (side-line and fly-over noise microphones). In the NINHA EU project microphones were flush mounted on a A320 (chase aircraft) front fuselage, prepared and operated by Airbus, to measure the noise coming from above (A400M). PropMat’s use of microphones mounted on a nose boom, in an area not impacted by engine noise, enables a much wider angular measurement range (including for noise coming from below). This meets for the first time the angular range that Airbus required for Open-Rotor measurements.

For separation of tonal and broadband noise in wind tunnel experimental acoustic data the state of the art is to couple the data averaging to the 1P signal of the rotor. This is no longer possible for CROR engines. PropMat provides the data processing method to separate the tonal and broadband noise for understanding the noise-generation mechanism of CROR engines based on acoustic wind tunnel data.

Acoustic testing in on scaled wind tunnel models requires also the appropriate scaling of acoustic liners, if present. A design approach has been developed, the first step of which consists of geometrical scaling. This has been applied to a number of samples which have been tested in an impedance tube. Further tuning steps have been prepared.

To understand the generation and propagation of noise inside the nacelle of a UHBR it is necessary to decompose the acoustic field into azimuthal modes. A study has been carried out on different concepts of instrumentation and mode detection methods. Recommendations have been derived for the design of the instrumentation and the choice of mode detection algorithm.

Regarding fan blade design the state of the art is to compute a steady-state shape pre-deformation correction to the metallic turbofan fan blade moulds. For many novel engine concepts the inflow is distorted and light-weight composite fan blades are used. State-of-the-art methods may be insufficient to fully cover the distortion effect. In addition, composite complicates the structural modelling. PropMat has set steps to model such composite fan blades at wind tunnel scale more accurately on the way to the final target of accuracy.

Regarding the wind tunnel experimental database from Clean Sky1, PropMat has extrapolated the database to a Mach number that could not have been tested. PropMat has also validated the extrapolation methods.

Expected impact

On the economic and environmental level PropMat’s results obtained so far are already key steps to reduce the development risk of emission-friendly aircraft with non-conventional acoustic behaviour. It is essential to have a deep understanding of and to master the behaviour of the innovative engines at all aircraft models (concept, wind tunnel model, flight test demonstrator, product aircraft) by numerical and experimental means.
On economic and socio-economic level PropMat therefore enables a technology leap by the European industry in the face of emerging competitors for large passenger aircraft. Investigations on emission-friendly aircraft such as Open Rotor, UHBR, and BLI concepts are not limited to Europe only. With the Clean Sky 2 LPA IADP Europe takes the lead to be the first to enter the market with environmentally and economically friendly aircraft.