Computational aeroacoustic analysis of propeller installation effects

Abstract

In line with the goal of cleaner and quieter aircraft, this paper investigates propeller acoustics aiming to improve turboprops noise emissions, as they represent the best choice for short and medium range flights in terms of fuel efficiency. CFD is used to analyse the propeller-airframe interaction physics, and assess propeller installation effects, for a full scale twinengined aircraft. The employed propellers represent advanced designs currently used in modern aircraft and the cases of co-rotating and counter-rotating top-in layout are considered. The URANS approach is used on grids of up to 195 M points aiming to directly extract from CFD the noise tonal content. Numerical results are first validated against modelscaled experimental data. A comparison between results of the full aircraft and a propeller in isolation is also carried out. Full aircraft predictions show significant differences in the external acoustics between port and starboard sides for the co-rotating case, with a louder noise generated by the inboard-up propeller. The counter-rotating layout shows a more regular distribution of overall noise, with on average slightly higher noise levels towards the front and the rear of the cabin. Acoustic predictions from an isolated propeller in axial flight significantly underestimate noise levels even on the fuselage sides where the aircraft masks the other propeller, showing the relevance of the propeller- airframe interactions in the evaluation of actual sound pressure levels in flight.