Aerodynamic Analysis of Conventional and Boundary Layer Ingesting Propellers

Abstract

The boundary layer ingestion (BLI) concept has emerged as a novel technology for reducing aircraft fuel consumption. Several studies designed BLI-fans for aircraft. BLI-propellers, although, have still received little attention, and the choice of open-rotors or ducted propellers is still an open question regarding the best performance. The blade design is also challenging because the BLI-propulsors ingest a non-uniform flow. These aspects emphasize further investigation of unducted and ducted BLI-propulsors and the use of optimization frameworks, coupled with CFD simulations, to design the propeller to adapt to the incoming flow. This paper uses a multi-objective NSGA-II optimization framework, coupled with 3D RANS simulations and Radial Basis Function (RBF) meta-modelling, used for the design and optimization of three propeller configurations at cruise conditions: (a) conventional propeller operating in the free stream, (b) unducted BLI-propeller and (c) ducted BLI-propeller, both ingesting the airframe boundary layer. The optimization results showed a significant increase in chord and a decrease in the blade angles in the BLI configurations, emphasizing that these geometric parameters optimization highly affects the BLI-blade design. The unducted BLI-propeller needs approximately 40% less shaft power than the conventional propeller to generate the same amount of propeller force. The ducted BLI-propeller needs even less power, 47%. However, the unducted and ducted BLI-configurations presented a higher backward force, 26% and 46%, respectively, compared to the conventional propeller, which can be detrimental and narrow the use of these configurations.