Experimental Identification of Noise Mechanisms Present in a Partially Buried BLI Ducted Fan

A comprehensive experimental investigation was conducted to analyze the noise generated by a boundary layer ingestion (BLI) ducted fan. The study focuses on the Bell X-22A-like ducted fan, which is partially immersed in a turbulent boundary layer developed over a curved S-plate. A thorough assessment was carried out under a wide range of fan thrust loading regimes. The flow field and noise measurements revealed that the noise originates from the complex interactions between ducted fan and the incoming boundary layer. Specifically, in high thrust conditions, the near-upstream region of a BLI ducted fan exhibits a predominant suction effect in the boundary layer. Consequently, the noise signature exhibits a structured pattern organized into haystacks, influenced by the strong interaction between fan noise and the boundary layer. Conversely, at low thrust conditions, the turbulent boundary layer ingests into the ducted fan without undergoing any suction effect. As a result, the noise signature features an altered haystack effects.