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Core noIse Reduction foR Uhbr engineS

Periodic Reporting for period 1 - CIRRUS (Core noIse Reduction foR Uhbr engineS)

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

The propulsion of the majority of commercial aircraft relies on turbofan engines. A gas turbine is used to drive the fan, which produces a significant part of the thrust. Modern turbofan designs rely on high bypass-ratios, meaning that most of the air flow goes through the bypass duct instead of entering the gas turbine. The current trend for future turbofan engines is towards even higher bypass ratios. These Ultra-High Bypass Ratio (UHBR) engines have large fans rotating at relatively low speeds. As a consequence of the lower fan speed, the fuel consumption can be reduced. Another consequence is that the engine noise signature is modified. The jet exhaust velocity is reduced and the jet noise is significantly decreased. Another benefit is that the low fan speed helps reduce the noise sources due to the fan. It is becoming urgent to tackle other noise sources on UHBR engines, specifically, the core noise generated by the combustion chambers and the turbine require particular attention since it is expected to become significant at certain operating conditions and strongly increased with the next UHBR 2030+ configuration where new clean combustor design and reduced LP turbine stages will be implemented.

The CIRRUS project aims to validate advanced low noise concepts, by developing both advanced numerical and experimental tools, to enable the reduction of the core noise in future UHBR 2030+ turbofan engines.

The overall goals of CIRRUS are to:
• Improve numerical methods to predict the noise source mechanisms and the acoustic core noise radiation up to the far field.
• Improve experimental methods, including new pressure and thermal sensors, to measure the contribution of core noise on real engines.
• Develop, test and integration of new generations of noise reduction acoustic liners made of Ceramic Matrix Composites (CMC).
• Investigate, by comparing various turbine configurations of future UHBR 2030+ architectures, the influence on the core noise sources that reducing the number of stages achieves.

The CIRRUS consortium is made of 5 partners covering a wide range of test and numerical expertise. With the maturation of a new generation of low noise solutions for the next generation of turbomachinery, the program will support the European society to reach a quieter environment in a near future. The project will contribute to the competitiveness of the European aeronautics industry with the access to a new generation of acoustic design tools and the acquisition of unique core noise experimental data base.
During the first period, the development of three main technologies has been started with first promising results.
On the simulation side, main actions are focused on the improvement of the physics to solve the combustion process in the chamber while a second action is dedicated on the extension of the acoustic radiation through the turbine stages. The third main action is focused on the resolution of the acoustic treatments along the wall of the exhaust in the frame of the evaluation of low noise solutions.
On the low noise solution, a technology screening has been conducted to evaluate the potential of Ceramix Matrix Composite acoustic liners. In parallel, the specification of a fist acoustic test campaign has been started with the use of a dedicated acoustic liner test bed.
Third main technology aims to address advanced acoustic methods to measure the contribution of the core noise. During the period, a selection of the most promising approaches and associated instrumentation (dynamic pressure and temperature) has been conducted with a first evaluation on synthetic data. In parallel, the identification of test vehicule and engine configurations has been conducted opening the starting of the experimental test campaigns in the next period.
Progress beyond the state of the art:
1. New physics in the evaluation of the combustion process and the radiation of acoustic waves
2. Implementation of advanced test methods to address core noise measurements
3. Identification of a new generation of core liners

Main expected results are:
• A new design suite for core noise prediction
• A new set of test methods for core noise measurements
• The acquisition of experimental core noise data base on full scale engine architecture
• The evaluation at full scale of the integration of a new generation of low noise solution
CIRRUS project Overview