Periodic Reporting for period 2 - SmartAnswer (Smart mitigation of flow-induced acoustic radiation and transmission for reduced aircraft, surface transport, workplaces and wind energy noise)
Période du rapport: 2019-01-01 au 2020-12-31
A step change in our noise mitigation strategies is required in order to meet the environmental targets defined for a number of sectors of activity affecting people through noise exposure, such as air / ground transportation and wind energy production. Radically new concepts for flow and acoustic control, such as meta-materials, porous treatment of airframe surfaces, airfoil leading-edge or trailing-edge serrations, … appear nowadays promising, however still largely as the result of extensive trial-and-error tests conducted at laboratory scale. It appears that the development and maturation of novel noise reduction technologies was hindered by several factors:
1) an insufficient understanding of the physical mechanisms responsible for the alteration of the flow or acoustic fields;
2) very tight design constraints are imposed to any novel noise mitigation strategy making its way to the full-scale application;
3) there is an insufficient knowledge about the possibilities that are nowadays offered by new materials and new manufacturing techniques.
SmartAnswer implements a research and training platform focused on innovative flow and noise control and optimization approaches addressing the above shortcomings. It has the following objectives:
- foster a training-through-research network of young researchers, where the ESR fellows investigate promising emerging technologies for noise reduction, by means of laboratory experiments, simplified theoretical models and numerical simulations.
- bring in a coordinated research environment industrial stakeholders picked from the aeronautical, automotive, wind turbine and cooling/ventilation sectors.
- offer a training infrastructure where the young researchers will be confronted with the design, manufacturing and economical constraints by strong interactions with the industrial final users.
The research carried out during the project addressed the noise generation and propagation mechanisms, and proposed innovative mitigation strategies accounting for their performance, complexity of integration, space, weight, durability, costs, etc. The research is relevant to many sectors of activity, addressing more specifically automotive cooling fans, wind turbine blades, aeroengines and building ventilation fans.
1) an insufficient understanding of the physical mechanisms responsible for the alteration of the flow or acoustic fields;
2) very tight design constraints are imposed to any novel noise mitigation strategy making its way to the full-scale application;
3) there is an insufficient knowledge about the possibilities that are nowadays offered by new materials and new manufacturing techniques.
SmartAnswer implements a research and training platform focused on innovative flow and noise control and optimization approaches addressing the above shortcomings. It has the following objectives:
- foster a training-through-research network of young researchers, where the ESR fellows investigate promising emerging technologies for noise reduction, by means of laboratory experiments, simplified theoretical models and numerical simulations.
- bring in a coordinated research environment industrial stakeholders picked from the aeronautical, automotive, wind turbine and cooling/ventilation sectors.
- offer a training infrastructure where the young researchers will be confronted with the design, manufacturing and economical constraints by strong interactions with the industrial final users.
The research carried out during the project addressed the noise generation and propagation mechanisms, and proposed innovative mitigation strategies accounting for their performance, complexity of integration, space, weight, durability, costs, etc. The research is relevant to many sectors of activity, addressing more specifically automotive cooling fans, wind turbine blades, aeroengines and building ventilation fans.
The mitigation of noise generating mechanisms was achieved through novel technologies including porous materials, leading and trailing edge serrations, and over-the-tip liners. The aeroacoustic effect of rod vortex generators, initially designed to delay flow separation, was investigated as well. Noise can also be attenuated during propagation by means of porous liners, micro-perforate panels and active impedance control. Finally, the transmission of noise through flexible panels has been attenuated by means of architected metamaterials.
In terms of exploitation potential, the industrial partners of the project and those invited in the Advisory Board have provided precious recommendations as to the applicability of the technologies to their fields. About source mitigation, serrations are being implemented on wind turbines, automotive low-speed cooling fans and building ventilation systems. Other technologies such as porous materials, regarded as a promising avenue to reduce airframe noise, will require further research in order to meet the tight airworthiness conditions that apply in the aeronautical sector. In this sector, passive liners have been extensively used for some time already, but the novel technologies proposed in the project (over-the-tip liners, micro-slit systems and active liners) open interesting perspectives. Another innovative noise control technology, based on architected metamaterials to attenuate transmission, show great potential as well. It should be finally stressed that some of the simulation technologies developed in the project, such as domain decomposition techniques for acoustic simulations, and adjoint-based optimization techniques, will find many fields of application beyond the sectors that were already represented in SmartAnswer.
The research outcomes have been continuously disseminated throughout the project evolution, concluding with the organization of a dedicated Lecture Series and open public Workshop. The ESRs have been actively involved in those events for the preparation and delivery of formal lectures to a broad audience constituted by PhD students, young professionals and more established researchers in the various fields addressed by the project. A last and very important tool for dissemination and communication towards both scientific experts and a broader audience is an aeroacoustic demonstrator, jointly developed by the project partners. It consists in a miniature wind tunnel, which gathers all the noise mitigation technologies developed by the ESRs.
Finally, it should be stressed that all the training program, and most of the ambitious secondment programme have been delivered despite the adverse conditions related to the Covid pandemic, requiring only minor adaptations.
In terms of exploitation potential, the industrial partners of the project and those invited in the Advisory Board have provided precious recommendations as to the applicability of the technologies to their fields. About source mitigation, serrations are being implemented on wind turbines, automotive low-speed cooling fans and building ventilation systems. Other technologies such as porous materials, regarded as a promising avenue to reduce airframe noise, will require further research in order to meet the tight airworthiness conditions that apply in the aeronautical sector. In this sector, passive liners have been extensively used for some time already, but the novel technologies proposed in the project (over-the-tip liners, micro-slit systems and active liners) open interesting perspectives. Another innovative noise control technology, based on architected metamaterials to attenuate transmission, show great potential as well. It should be finally stressed that some of the simulation technologies developed in the project, such as domain decomposition techniques for acoustic simulations, and adjoint-based optimization techniques, will find many fields of application beyond the sectors that were already represented in SmartAnswer.
The research outcomes have been continuously disseminated throughout the project evolution, concluding with the organization of a dedicated Lecture Series and open public Workshop. The ESRs have been actively involved in those events for the preparation and delivery of formal lectures to a broad audience constituted by PhD students, young professionals and more established researchers in the various fields addressed by the project. A last and very important tool for dissemination and communication towards both scientific experts and a broader audience is an aeroacoustic demonstrator, jointly developed by the project partners. It consists in a miniature wind tunnel, which gathers all the noise mitigation technologies developed by the ESRs.
Finally, it should be stressed that all the training program, and most of the ambitious secondment programme have been delivered despite the adverse conditions related to the Covid pandemic, requiring only minor adaptations.
On a general level, the project has brought a very significant contribution to the advancement of innovative noise mitigation technologies. The ESRs have been able to bring a lot of insight as to the physics involved in their mitigation. Novel models have been elaborated, which will enable the future optimization of the various technologies and facilitate their adoption by industry.
Porous materials and serrations have demonstrated a good potential for the mitigation of the noise produced by turbulence-surface interactions. The main parameters driving the noise attenuation have been investigated numerically through high-fidelity techniques, and advanced analytical models have been proposed to justify the physical mechanisms responsible for the noise reduction. Another innovative use of acoustic treatments to reduce noise at the source is to place liners over the fan rotor tip on turbofan engines. The results have shown a great potential for reducing fan noise sources. It should be noted that this technology could be easily ported to other sectors of activity such as the propulsion systems of the new aircraft architectures that are considered for urban air mobility.
The availability of new manufacturing techniques for producing anisotropic light micro-perforates with large steady pressure drops and still significant acoustic absorption properties has opened interesting perspectives of integration in ventilation ducts and low-speed cooling/ventilation fans. But high level complex multi-frequency acoustic excitation yields insufficiently understood interaction effects. The combination of high level multi-frequency acoustic excitation and grazing flow or bias flow in the experiments has provided useful data in that respect.
Metamaterials have been studied not only in terms of theoretical absorption / transmission but also, in a more engineering way, to evaluate their sensitivities to sound pressure levels and to grazing flow effects. Likewise, non-local passive and active MDOF liners are currently designed with the assumption that they are locally reacting, however several advanced liner concepts involve non-local impedance. The necessary physical modelling efforts has been carried out jointly with the development of advanced numerical methods. This should eventually promote the advent of lightweight materials with application in many engineering fields.
Porous materials and serrations have demonstrated a good potential for the mitigation of the noise produced by turbulence-surface interactions. The main parameters driving the noise attenuation have been investigated numerically through high-fidelity techniques, and advanced analytical models have been proposed to justify the physical mechanisms responsible for the noise reduction. Another innovative use of acoustic treatments to reduce noise at the source is to place liners over the fan rotor tip on turbofan engines. The results have shown a great potential for reducing fan noise sources. It should be noted that this technology could be easily ported to other sectors of activity such as the propulsion systems of the new aircraft architectures that are considered for urban air mobility.
The availability of new manufacturing techniques for producing anisotropic light micro-perforates with large steady pressure drops and still significant acoustic absorption properties has opened interesting perspectives of integration in ventilation ducts and low-speed cooling/ventilation fans. But high level complex multi-frequency acoustic excitation yields insufficiently understood interaction effects. The combination of high level multi-frequency acoustic excitation and grazing flow or bias flow in the experiments has provided useful data in that respect.
Metamaterials have been studied not only in terms of theoretical absorption / transmission but also, in a more engineering way, to evaluate their sensitivities to sound pressure levels and to grazing flow effects. Likewise, non-local passive and active MDOF liners are currently designed with the assumption that they are locally reacting, however several advanced liner concepts involve non-local impedance. The necessary physical modelling efforts has been carried out jointly with the development of advanced numerical methods. This should eventually promote the advent of lightweight materials with application in many engineering fields.