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Support to Future CROR and UHBR Propulsion System Maturation

Periodic Reporting for period 2 - PropMat (Support to Future CROR and UHBR Propulsion System Maturation)

Reporting period: 2017-07-01 to 2018-12-31

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 now 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. The associated results are:
• Innovative numerical and experimental methods and tools as needed for aerodynamic &-acoustic characterisation, blade aero-elastic deformation, acoustic measurement techniques, acoustic ground instrumentation, chase aircraft flight testing, and impact numerical simulation and tests.
• 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 worked on an innovative chase aircraft acoustic in-flight measurement methodology. The feasibility of the measurement method has been investigated in an experimental test campaign in which NLR’s Citation aircraft has been measuring the noise of a propeller aircraft. Theanalyses of the experimental data,initial conclusions and recommendations, were presented to Airbus. The work has resulted in the feasibility of the innovative chase aircraft acoustic in-flight measurement methodology to provide accurate measurements in all directions and at various distances from the flying demonstrator of an innovative engine configuration, in various operational conditions, as demonstrated on a propeller aircraft.

Secondly, a data processing method has been developed to separate tones and broadband noise in wind tunnel experimental acoustic data. The method is based on a so-called Vold–Kalman filter, which uses the 1P signals of both rotors of a CROR configuration. The method has been validated successfully on multiple data sets from two different wind tunnel tests and is ready for exploitation.

Thirdly, wind tunnel experimental data were extrapolated. During the Clean Sky 1 programme the CROR configuration was operated in the large open test section of the DNW-LLF low speed wind tunnel at maximum velocity. Airbus however required data at higher Mach numbers for representativeness at aircraft take-off. Numerical techniques were validated with the DNW-LLF experimental data. Next the DNW-LLF experimental data base was extrapolated to higher Mach numbers.

Fourthly, the structural modelling of propeller blades of CROR configurations was investigated for aero-elastic blade deformation. Finite element models have been developed with improvements. Experimental data of CROR propeller blades at wind tunnel scale were better represented with some errors in the structural model decreasing nearly 50%. In addition it was investigated how the methods for CROR propeller blades could be used for UHBR fan blades.
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). Compared to the acoustic chase aircraft during the NINHA EU project, where microphones were flush mounted on a A320 front fuselage, prepared and operated by Airbus, to measure the noise coming from above (A400M), here the 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.

Regarding aero-elastic blade deformation 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 propeller and 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 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 such behaviour 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.
Flight test of the innovative chase aircraft acoustic in-flight measurement method
Detailed analysis of propeller noise measured during flight test of PropMat’s innovative chase aircr
View from NLR’s Citation research aircraft on the propeller aircraft of which the noise is measured
Validation of wind tunnel data processing method for separation of broadband and tonal noise
Extrapolated pressure distribution from DNW-LLF wind tunnel test
Finite element model of fan blade with foot in Abaqus
NLR's Citation research aircraft equipped with nose boom with acoustic sensors
Extrapolation of DNW-LLF acoustic results to higher Mach numbers