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Support to Future CROR and UHBR Propulsion System Maturation

Periodic Reporting for period 4 - PropMat (Support to Future CROR and UHBR Propulsion System Maturation)

Reporting period: 2020-07-01 to 2021-12-31

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 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)
1) An innovative chase aircraft acoustic in-flight measurement methodology was experimentally with NLR’s Citation aircraft 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.

2) 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.

3) A design approach for geometrically scaled liners in wind tunnel models has been developed, taking into account performance requirements, manufacturing, and testing constraints. The design approach was verified on eight samples. Parameters of the scaled liners have been tuned.

4) Wind tunnel experimental data in the DNW-LLF data base for the CROR configuration from Clean Sky 1 were extrapolated to higher Mach numbers for representativeness at aircraft take-off. The numerical extrapolation techniques were validated with the DNW-LLF experimental data.

5) Design methods and advanced finite element modelling methods were developed to extend the aeroshape of the fan blade at wind tunnel scale to a full composite fan blade structure, including ply lay-up and orientation, for accurate manufacturing. Design and modelling methods were verified on coupon and element levels, verified against the fan aeroshape from the EU ASPIRE project, and later applied for an UHBR wind tunnel test.

6) Numerical methods were developed to represent both buzz saw noise (dominant sound source at take-off) and the behaviour of acoustic liners (to reduce engine noise) in the intakes of turbofans in CFD-based simulations. The method for acoustic liners was validated through an experiment in a liner test facility. Realistic sounds were obtained when simulating buzz saw noise in a UHBR engine. The effectiveness of the acoustic liners in attenuating the buzz saw sound waves could be quantified.

7) A new generation of rotating balances was developed for force and moments measurements in wind tunnel models of engines. A defect free topology-optimised balance demonstrator was additively manufactured.

8) A concept for a data acquisition system was developed for a large number of dynamic sensors (microphones and pressure sensors) in the limited space of a UHBR wind tunnel model. A technology demonstrator has been built and its functionality has been validated.
Progress beyond state of the art and specific expected potential impact

1) Take-off and approach acoustic characteristics of an aircraft are measured using ground instrumentation. In the NINHA EU project microphones were flush mounted on a A320 (chase aircraft) front fuselage to measure the noise coming from above (A400M). PropMat’s method with microphones mounted on a nose boom, not impacted by engine noise, enables a much wider angular measurement range, meeting for the first time the angular range required for Open-Rotor measurements.

2) The state of the art data processing method for separation of tonal and broadband noise in wind tunnel experimental acoustic data of turbofans is no longer possible for CROR engines. PropMat provides the method to separate the tonal and broadband noise for understanding the noise-generation mechanism of CROR engines.

3) The scaling/tuning technologies developed for acoustic liners in wind tunnel models are a major step forward to wind tunnel testing with representative acoustic liners, which results in better prediction of the full scale acoustics.

4) The wind tunnel experimental database from Clean Sky1 could be extrapolated to a Mach number that could not have been tested.

5) For metallic fan blade design for wind tunnel models the state of the art is to compute a steady-state shape pre-deformation correction. PropMat has set steps to model light weight composite fan blades at wind tunnel scale more accurately on the way to the final target of accuracy.

6) The novel integration of acoustic liners in CFD computations allows to better predict their contribution to community noise reduction, which previously could not be done. Combined with novel numerical representation of buzz saw noise, this is an essential enabler for industry to master (short-inlet) UHBR engines community and cabin noise during approach.

7) The novel manufacturing method for rotating balances gives opportunities for increased measurement accuracy, while reducing manufacturing cost and time. The new generation of rotating balances thus obtained enables better predictions about the full scale next-generation engine design.

8) The demonstrated concept of the dynamic data acquisition system enables significantly more aerodynamic and aero-acoustic sensors to be used than presently. With the ever increasing needs for such measurements when advancing engines, this will be the dynamic data acquisition system for the next generation wind tunnel models.

Expected impact (overall)

Economic and environmental: PropMat’s innovations on numerical and experimental means are key steps to obtain a deep understanding of and to master the behaviour of innovative engines at all aircraft models (concept, wind tunnel model, flight test demonstrator, product aircraft). This reduces the development risk of emission-friendly aircraft with non-conventional acoustic behaviour.

Economic and socio-economic: PropMat therefore enables a technology leap by the European industry in the face of emerging competitors for large passenger aircraft which are also investigating emission-friendly aircraft such as Open Rotor, UHBR, and hydrogen burn concepts. With the Clean Sky 2 and Clean Aviation, Europe takes the lead to be the first to enter the market with environmentally friendly aircraft.
Validation of wind tunnel data processing method for separation of broadband and tonal noise
Generic concept of PropMat DynDAS technology demonstrator
Master module of DynDAS demonstrator (on the left) with a single chain, consisting of two slave modu
Topology optimized rotating balance design developed at NLR
manufactured geometrically scaled liners for in-situ impedance testing in flow duct facility (scale
Extrapolation of DNW-LLF acoustic results to higher Mach numbers
Detailed analysis of propeller noise measured during flight test of PropMat’s innovative chase aircr
NLR's Citation research aircraft equipped with nose boom with acoustic sensors
Extrapolated pressure distribution from DNW-LLF wind tunnel test
Campbell diagram for fan blade external aeroshape, extended by PropMat with blade foot and internal
Verification of three candidate methods for acoustic mode detection (green) in the inlet of a UHBR a
Tensile test of element representative for composite fan blade with foot of a UHBR engine at wind tu
Flight test of the innovative chase aircraft acoustic in-flight measurement method
Finite element model of fan blade with foot in Abaqus
View from NLR’s Citation research aircraft on the propeller aircraft of which the noise is measured