On the Unsteady Fuselage Loading Induced by a Proximal Propeller

Aircraft cabin noise and structural loading can be strongly influenced by the surface pressure fluctuations experienced by the fuselage as fuselage loading. Fuselage loading can vary significantly depending on the particular aircraft-propulsion arrangement since propulsion systems typically exhibit strong cyclic loads which propagate to the fuselage. The current study reports an experimental study in the case of a propeller operating in close proximity to a surface. The experimental setup consists of a propeller placed adjacent to a flat plate subjected to freestream flow, the propeller distance from the plate is varied which allows the boundary layer ingestion (BLI) scenario to also be evaluated. Three boundary layers of varying characteristics are tested. The plate surface is instrumented with streamwise pairs of surface pressure transducers to allow measurement of the pressure fluctuations and coherence. Results are compared to a base 'hub-only' case to isolate the effect of the propeller. The semi-empirical wall pressure model, Corcos, is used to predict the coherence spectra of the wall pressure fluctuations. It was found that the propeller induces strong tonal contributions and reduces low (<100 Hz) content in the energy spectra. It was observed that the applicability of Corcos to predict the coherence spectra is strongly dependent on the boundary layer thickness, the degree of boundary layer ingestion, and propeller operating speed. The Corcos coefficients that allow fitment to the empirical data where possible are provided. This study highlights the limitations of simple wall pressure models in the case of more complex airframe configurations.