Effects of Sideslip Direction on a Rear Fuselage Boundary Layer Ingesting Fan

Abstract

Boundary layer ingestion (BLI) offers potential reductions in fuel burn and emissions. The propulsive fuselage concept features an aft fan that ingests the 360 deg fuselage boundary layer. A critical condition for this configuration occurs when a sideslip angle arises between the aircraft longitudinal axis and the freestream velocity. The sideslip flow in combination with the airframe generates inlet distortion that depends on the sideslip direction. In particular, the sideslip increases flow into the windward side of the intake and reduces the flow on the opposite side, leading to either coswirl or counterswirl at the fan face. This article investigates the effect of sideslip direction on the aerodynamics of an aft BLI fan. Experimental measurements have been taken in a lowspeed fan rig with representative total pressure and swirl distortion. These tests have been complemented by fullannulus unsteady Reynoldsaveraged Navier–Stokes simulations to understand the impact of sideslip on the rotor and outlet guide vane flow fields. The results show that positive sideslip (sideslip that produces counterswirl) increases the fan work and incidence, but the additional losses are relatively small. However, negative sideslip results in lower loading, negative incidence, and greater losses. The stage loading was 28% higher and the stage efficiency was 1.65% higher for positive versus negative sideslip. The positive sideslip case was also found to lose some operating range, equivalent to 2% of nozzle area. Overall, the fan design tolerates the sideslip distortion well and demonstrates the importance of the coupling of both swirl and total pressure distortion with the fan aerodynamics.