Experimental investigation of boundary layer ingestion in integrated propulsion systems

Abstract

This thesis experimentally assesses the benefit of Boundary Layer Ingestion (BLI) at the unaccelerated condition (thrust equals drag) of an integrated system in an industrial wind tunnel setting. The boundary layer or wake flow of the fuselage is ingested by the propulsor. Previous research shows that ingesting the boundary layer can lead to beneficial savings in terms of power compared to a compared to a non-BLI propulsor. Traditional thrust-bookkeeping methods are not suitable for BLI systems because of the ambiguity between thrust and drag of BLI systems. In order to analyse the performance of such integrated systems the theoretical framework developed by Mark Drela is used: the Power Balance Method (PBM). Furthermore, the classical definition of propulsive efficiency, also named "Froude" efficiency, is not valid for these systems, thus a relatively new propulsive efficiency definition is used. The wind tunnel tests were carried at the Low Speed Wind tunnel (LST) from the German-Dutch Wind tunnels (DNW) located in Marknesse. Four different configurations were tested in the wind tunnel: i) isolated propulsor, ii) isolated propulsor including an upstream strut, iii) BLI configuration and iv) Wake Ingestion (WI) configuration. The isolated propulsor, simply a propulsor in free-stream flow, is used as a reference to compare with the BLI system. The unaccelerated condition at which these systems were tested is at Mach number M = 0:176. The mechanical flow power, jet dissipation and propulsive efficiency are quantified experimentally by using a five-hole probe. Other relevant physical parameters are also measured such revolutions per minute (RPM), thrust and body drag. The designed fuselage is axisymmetric simplifying the measurements and computations. The results from the experiment reveal that BLI systems have power savings around 29% 2:9% when using the electrical power as a reference compared to the non-BLI system. For WI the power savings are slightly lower 24% 2:9%. Moreover, the power savings have also been computed using the mechanical flow power, but a larger variance has been observed in the results from 29:25% up to 56:27% for the BLI case. The flow specially at the outlet plane is shown to be asymmetric between the starboard and port sides. Furthermore, the jet dissipation decreases by 27% compared to a non-BLI system. The slow moving wake flow of the fuselage is re-energized leading to a decrease in jet dissipation. The propulsive efficiency increases between 8% to 10% for both BLI and WI configurations compared to the free-stream propulsor.