Aeroacoustics of 2-D and 3-D Blade Vortex Interaction Using the Indicial Method

The aeroacoustics of blade vortex interaction (BVI) has been modeled using the indicial method combined with the acoustic analogy in the form of the Ffowcs Williams-Hawkins (FW-H) equation. The general philosophy has been to explore the capabilities and limitations of the indicial method as it would be employed in a comprehensive rotor analysis. A set of generalized sharp-edged gust functions were derived using both exact subsonic linear theory and indicial computations with a finite-difference (CFD) method. Results for arbitrary gusts were then obtained using Duhamel superposition. For a nominally 2-D BVI problem, numerical comparisons with CFD and also with experimentally measured airloads were found to be good. Finally, the indicial method was integrated into a three-dimensional rotor simulation, and the near and far-field acoustics were computed using the FW-H equation. Good agreement was found with simultaneously measured airloads and acoustics data.