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Validation of improved turbomachinery noise prediction models and development of novel design methods for fan stages with reduced broadband noise

Periodic Reporting for period 3 - TurboNoiseBB (Validation of improved turbomachinery noise prediction models and development of novel design methods for fan stages with reduced broadband noise)

Reporting period: 2019-09-01 to 2020-08-31

The technical objective of TurboNoiseBB is the development of concepts and enabling technologies aimed at reducing aeroengine noise at source. The addressed fan broadband noise (BBN) is a major aircraft noise challenge. TurboNoiseBB enables a major technical leap in providing the industry with low fan broadband noise concepts, based on an improved understanding of the broadband noise source mechanisms and validated broadband noise prediction methods.
The quantitative objective of TurboNoiseBB was to provide a 3 dB reduction at source on fan noise alone. In the process, TurboNoiseBB was to advance the current noise technologies to higher TR-levels. The plan was to raise the TRL of innovative low noise OGV concepts from 2-3 up to 4-5 by performing large scale fan rig tests. High fidelity CFD/CAA computations advance the state-of-the-art CFD/CAA broadband noise design methods to a higher level that can be integrated within industry-exploitable tools.

The outlet Guide Vane (OGV) design with leading edge serrations for BB noise reduction was lifted from TRL3 to 5. The parametric 3D design of low BB noise OGV through numerical tool was increased from TRL3 to 5.
The TRL of the integrated 3D Aero/Mech/Noise Design for low BB noise OGV was brought from 2 to 5. Semi-analytical methods based on simplified geometries and fed by CFD-based turbulence information wer developed from
TRL 4 to TRL5. The technology readiness level of LES simulations of rotor-stator stage for BB noise prediction was lifted from 3 to 4.
The TRL of CAA (LEE) simulations of rotor-stator stage for BB noise prediction was increased from 2 to 3. The DES simulations of rotor-stator stage with blade count approximation for BBN prediction were brought up from 1 to a TRL of 3.
Finally, the turbine Broadband Noise Model (derived from Fan method) validated against engines database was increased from TRL 1 to 3.
All specifications for the tests, for the simulation work as well as for the data formats and the benchmarking have been issued and documented in collaboration between industrial
key players, research etsablishments and universities. The turbine related work made excellent progress: The industrial partners made use of the fan measurement data,
validated their codes and prepared a read-across to in-house turbine data in order to improve the turbine noise predictions codes.

The unpreceded BBN fan test was completely conducted and delivered an enormous amount of precious measurement data. All measurement data were documented and the
test conditions well described. The database was distributed to all partners, who needed them for their further activities in the project. The data analysis and appraisal was
completed. In the frame of this, an substantial amount of information has been analysed. The appraisal provided the certainty that the data sets are of maximum value,
quality and completeness. The acquired data sets will serve as reference data for fan BB noise and will establish a data-base, which did not exist before. It is
unique in the world in its richness, quality and depth of information.

The benchmark tests as well as a first stage of numerical predictions based on the reference fan geometry were already undertaken.
A lot of numerical results were achieved and could be compared with the experimental outcome of the elaborated fan tests.

A design of an aerodynamically optimized OGV is available for the second stage of the optimization process, being acoustically orientated both on tonal as well as on BBN.
The first stage of the optimization scheme has been accomplished.

The design phase for a novel, serrated, acoustically optimized OGV set has been completed.
The final design was chosen and the high-fidelity simulation work exhibits good progress.
The accurate modelling of a representative turbulence in an aero-engine fan stage is still a huge challenge in all current industry-based design methods. TurboNoiseBB will provide for the first time a step further into the integration of the higher accuracy CFD/CAA methods aforementioned into the multi-disciplinary fan-stage design. Comparisons with the experimental database, acquired using advanced aero-acoustics measurement techniques on the large scale UHBR fan stage (Anecom rig), will highlight the added value of the high fidelity CFD/CAA methods relative to industry RANS-based methods. Experimental results from parametric studies of fan/stator spacing, which shows significant difference in noise and flow behaviour will also be accurately captured through large scale testing at Anecom and will strengthen the quality of the database across the whole of the UHBR fan stage design space.

The final achievements of the project are
1) The unpreceded BBN fan test was completely conducted and delivered an enormous amount of precious measurement data.
2) All measurement data were documented and the test conditions well described. The database was distributed to all partners, who needed them for their further activities in the project.
3) The data analysis and appraisal were completed. In the frame of this, a substantial amount of information has been analyzed. The appraisal provided the certainty that the data sets are of maximum value, quality and completeness.
4) The acquired data sets establish a data-base, which did not exist before. It is unique in the world in its richness, quality and depth of information.
5) Various numerical predictions based on the reference fan geometry were undertaken.
6) The numerical results of four different numerical simulation methods (analytical, (U)RANS, stochastical turbulence based and scale-resolving) and combinations with acoustic prediction schemes were achieved and could be compared respectively with the experimental outcome of the fan tests.
7) Two benchmarks dealing with the impact of 1) turbulence model in RANS simulations and 2) acoustic analytical models in RANS-informed analytical prediction were organized. Over 10 partners were involved in this activity.
8) A design of a classical, aerodynamically optimized OGV is available from WP5, being further optimized acoustically both in terms of tonal as well as on BB noise.
9) The design of a novel, serrated, acoustically optimized OGV set has been completed in WP6. Its aeroacoustic BBN reduction potential has been thoroughly investigated by means of high-fidelity CFD and CAA simulation work.
10) Airbus performed a final assessment of the turbine predictions at aircraft level
10a) A sensitivity study shows that LR aircraft noise level is sensitive (more than 0.1EPNdB variation) to turbine broadband noise prediction uncertainty, when the turbine broadband noise is 2dB over predicted
10b) The TurboNoiseBB project allowed to improve the turbine acoustic prediction methods successfully within this 2dB overprediction limit.
11) Airbus performed a final assessment of the low noise OGV designs at aircraft level
11a) The OGV design showed a significant reduction of fan tonal noise but an increase of broadband noise, which led to no reduction of noise at aircraft level at approach and cutback.
11b) The serrated OGV design showed a promising reduction of EPNL at approach up to 0.7dB assuming the same reduction on the forward broadband
Example of acoustic mode decomposition using advanced analysis techniques
Large eddy simulation: Vorticity iso-contours near the OGV blades
Investigated model fan geometry
Numerical simulation result: Entropy contours in the vicinity of the fan
ANECOM Fan rig in anechoic room