Aerodynamics and Aeroacoustics of Propeller Operation at Negative Thrust: A Computational Study

Future regional and short to medium-range aircraft are expected to use propellers for sustainable aviation, possibly with (hybrid-)electric propulsion systems. This will enable innovative integration of aero-propulsive systems, potentially increasing the overall aerodynamic efficiency of the airframe and propellers, resulting in a lighter airframe and increased passenger comfort. The presence of electric motors and propellers in such configurations, in addition, offers a unique opportunity to leverage propellers as airbrakes by operating them at negative thrust. This approach offers multiple potential advantages, including shorter landing runs, enhanced landing maneuverability, energy harvesting during braking operations, faster aircraft turnaround times, and reduced community noise exposure.

Despite these potential advantages, the aerodynamic and aeroacoustic characteristics of propellers operating in negative thrust mode remain largely unexplored. This dissertation addresses this knowledge gap through computational analysis, comparing the performance of isolated propeller configurations in negative thrust mode with the well-understood positive thrust mode. The results reveal that the distinct aeroacoustic characteristics of propellers operating in negative thrust conditions, compared to conventional positive thrust conditions, offer a promising avenue for reducing community noise, not only through the possibility of steeper descents but also through changes in the noise emissions from the propeller itself.