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Silent Air Flows in transport, buildings and power generation

Final Report Summary - FLOWAIRS (Silent Air Flows in transport, buildings and power generation)

Noise pollution has become one of the environmental pressures that closely affect European citizens, with overall nuisances and health problems. A new approach in noise control solutions is necessary to comply with EU legislation and enhance people quality of life. Thus, there is a real need for a European-wide training in the study of generation, propagation and reduction of sound in flow ducts for transport, buildings and power generation to put Europe in a leading position in the field and foster the competitiveness of the EU industry.

In this sense, FlowAirS gathered a network of European and an Egyptian specialists in aero- and vibro-acoustics, from both the academic and private sector (11 full partners and 5 associated partners), who actively collaborated in training by research a new generation of researchers to make their careers more attractive and enhance their professional opportunities. 18 young researchers (14 Early Stage researchers and 4 post-doctoral fellows) have been involved in the project, 28% of them being women.
Research activities were divided in three main fields: the study of noise production mechanisms and noise propagation, the development of innovative noise reduction techniques, and the improvement of prediction methodologies.

Two of the fellows have studied the noise produced by rotating machines. In one case the fellow has demonstrated that the noise can be a diagnostic tool to predict when a turbo-charger instability starts to occur. The other one develops a new clever method to determine, with a small computational effort, the broadband noise due to turbulence impacting on a fan. This will allow an optimization procedure for the blade design.
Two other fellows have worked on the self-sustained pulsations occurring when acoustic and flow interact near an obstacle in a duct. For one of the students, these obstacles were two diaphragms and for the other two side branch resonators. In this case, a focus has been given on the added acoustical attenuation due to water in a pipe with a two-phases flow containing both air and water.
The development of accurate and economical numerical acoustic prediction tools has been the subject of two fellows. One of the fellows works on a code that predicts the temporal evolution of a wave. A particular attention has been given to the temporal response of the absorbing material, which is very difficult to model. The other student has worked on a very high precision and robust code for a wave at a given frequency taking into account most of the flow effects. Studies are actually engaged at Siemens Industry Software to eventually industrialize and commercialize this tool.
Another topic of this project was the development of innovative noise reduction techniques. Two of the students have worked on metamaterial I.e. material with special proprieties non reachable by classical materials. Among the studied concepts, there were soft metallic patches, resonators embedded in porous materials and materials with labyrinthine shape. One of these students also studies the way of creating a new absorption peak by an interference effect along the material. Another studied concept was the new compact muffler that uses micro-perforated material and a perfectly matched condition. A student has made a more fundamental work on the non-linear behaviour of the resonator at high amplitude and on the flow-noise coupling near the transition from a rigid wall to an absorbing material.
The last topic concerns the improvement of prediction methodologies. Two students apply high-fidelity numerical flow simulation methods such as large-eddy simulation (LES) to study sound generation from obstacles in ducts. One fellow simulates with compressible CFD the flow-acoustic coupling of in-duct orifices (single and double-orifice configuration) and develops a procedure for concurrent identification of both the acoustic scattering and the sources of broad-band noise. The other fellow computes the flow around a three-dimensional obstacle representing an industrial baffle silencer. Those calculations and the experiments made by other fellows (like measurements on the double-orifice configuration, on baffle silencers done at Müller-BBM on the thermostatic expansion valve of an automotive refrigerant circuit done at Audi) are used to identify systems. This allows analysing the different configurations and phenomena responsible for noise generation.

In addition to the training through research at the host institution, FlowAirS fellows had an insight in the complexity of industrial issues and an opportunity of training in an extra-academic framework through the secondments. Compulsory courses and workshop, common to all fellows, have also been organised in order to provide them with indispensable skills. Thank to this, FlowAirS young researchers gained a multi-disciplinary and appropriate background in their field.
The industrial associated partners helped to define the training program according to identified needs. Furthermore, the partners kept permanent contact and met regularly to have an overview of the project progress and to discuss the upcoming steps. Networking activities have also been organised in order to allow the fellows to get to know each other better and to strengthen the relationship among the network members.

After 4 years of close collaboration, FlowAirS project ended in November 2015 having achieved most of its objectives and technical goals.

For more information:
Yves Aurégan, coordinator: