Characterization of simulated jet noise by means of spherical harmonics decomposition
- Research Area:
Akustische Virtuelle Realität
Master Thesis of Cappellotto, Francesco
This thesis presents a research on the source modeling of aircraft’s jet noise, the goal of which is to reproduce the sound of aircraft in simulated Virtual Reality environments with a high degree of fidelity. At the moment, the acoustical modeling of jet noise follows semi-empirical models, partially derived from fly-over measurements and optimized to include a set of variable configurations, e.g. noise reducing chevrons. However, this method has some limitations. In fact, its spectral resolution is limited to one-third octave bands, and the correlation of single noise components is not defined. Moreover, ground measurements require some approximations to account for the cutback phase (a reduction in the power level right after take-off). This affects not only the power level, but also the directivity of the jet noise, which cannot be approximated due to lack of information. Finally, ground measurements are normalized to standard atmosphere, thus the uncertainty derived from the current weather at the time of the measurements is included in the directivity. In the scope of this thesis a method will be researched, to model the noise of jet engines in a more precise way, using simulated data to compute physically valid directivity patterns, rather than empirical or semi-empirical models, and to achieve results that are independent from meteorological conditions and not restricted to one-third octave bands. To do so, simulated data on a 3d-grid in the near far-field around the jet will be used as input data. A set of points has to be chosen and modeled using spherical harmonics decomposition. Since it is expected that the model will reach high-order spherical harmonics, an acoustic centering of the source will be evaluated to reduce the computational cost. With the use of this method, it is expected to achieve a better auralization, which can be used for more realistic VR simulations.