Abstract
The present study focuses on the prediction of ground-based tonal noise generated by a twin-turboprop aircraft in cruise flight at different heights and thrust conditions, by means of a CFD/CAA-based approach. The unsteady flow solution of the 1:1 scale model is obtained by using the Lattice-Boltzmann/Very Large Eddy Simulation method. Numerical predictions are validated against noise measurements conducted on the entire aircraft configuration. Microphones were positioned both parallel and perpendicular to the flight path, in order to capture the directivity of the aircraft noise.
The far-field noise spectra, computed via the Ffowcs-Williams and Hawkings´ acoustic analogy applied to the propeller and airframe surfaces, show a good correspondence between the numerical and experimental results at the first and second blade passing frequencies. Furthermore, the on-ground noise footprints reveal that the employed method is able to capture the complex acoustic field generated by the propellers and its scattering on the airframe. Finally, the noise signatures over time at prescribed ground microphone locations are calculated using an atmospheric propagation model based on a ray tracing method.
