This project aims to improve understanding of core noise from aero engines with low emission combustors and provide industry with analytical tool that can be used to predict the noise when designing future engines, thereby enabling quieter designs.
The Horizon 2020 goals are a 75% reduction in CO2 emissions per passenger km and 90% reduction in NOx, while the perceived noise is reduced by 65%.
However lean burn combustor technologies introduced to reduce NOx are proving to be inherently noisier than conventional combustors, generating broadband noise that can be heard external to the aircraft. Without careful design and optimisation, the low emission cores may cause aircraft engines to exceed the noise requirement.
The research in this project aims at understanding the flow physics involved in generation and propagation of core noise in low emission cores. It includes both direct noise of combustion, pressure waves generated directly by unsteadiness in the rate of combustion, and indirect noise generated as entropy waves accelerate through the Nozzle Guide Vanes (NGVs) and propagate through turbine blade rows.
The objectives are to:
• predict the turbulent reacting flow field in a low-emission combustor at engine conditions
• predict the generation of indirect noise and the propagation and interaction of acoustic and entropy fluctuations in a high-pressure turbine stage in an aero-engine
• develop a combustion noise prediction tool that can be used by industry to design quieter engines
• quantify experimentally the combustor unsteadiness in an aero-engine representative low-emission combustor and validate the modelling.
The conclusions of the project are:
• The FlaRe combustion model incorporated within the industry partner’s in-house LES (Large Eddy Simulation) code has been has been extensively validated through comparison with unsteady temperature data.
• The comparisons of LES results for single and double sector combustors show that single sector models and experiments should be sufficient to investigate indirect noise.
• High fidelity computations of the unsteady flows in turbine blade rows have identified the main causes of redistribution of temperature fluctuations as they propagate through a turbine. These can be captured in a low-order model that gives excellent agreement with the computational results.
• The experiments have demonstrated for the first time high-speed optical measurement of temperature profiles in a high-pressure combustion environment representative of an aero-engine. These have been validated near combustor exit by excellent agreement with the LES.
