Partially resolved numerical simulation of flow-induced aircraft noise

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This proposal is motivated by the fact that the largest ever European aircraft noise research project, known as SILENCE(R), was launched in April 2001. A consortium of 51 companies have collaborated for 4 years to validate new technologies for reducing aircraft noise by up to 6 decibels (dB) as of 2008. The total budget exceeds 110 million Euros.    Aircraft noise, categorized by airframe and jet noise, has become an increasingly important factor in aircraft design due to its environmental impact on the areas surrounding airports. At takeoff, when the engine is operating at full thrust, the main source of noise is the jet. Although jet noise can be reduced by choosing a turbofan engine with a high bypass ratio, in practice, the maximum bypass ratio is still limited by physical factors such as the length of the fan blade. An alternative approach is to introduce chevrons and tabs in a nozzle to enhance mixing between core, fan and ambient air streams at the expense of engine efficiency.    It is believed that a better understanding of the source mechanism, in which turbulence plays a very important role, will facilitate the generation of new noise-reducing concepts. It is against the above background that a research program is put forward in which both airframe and jet noise will be investigated by adopting a hybrid approach, in which the instantaneous near-field flow solutions will first be obtained with Partially Resolved Numerical Simulation.  The far-field sound can then be calculated using a separate integral method (e.g., the Ffowcs Williams and Hawkings method or the Kirchhoff method) using the source terms obtained from the previous near-field flow solutions.