Aerodynamic benefits of boundary layer ingestion for the D8 double-bubble aircraft

Abstract

This thesis describes experimental assessments of the aerodynamic boundary layer ingestion (BLI) benefit of the D8 advanced civil aircraft design. Two independent methods were applied for 1:11 scale (4.1 m wingspan) powered aircraft model experiments in the NASA Langley 14x22-foot Subsonic Wind Tunnel. The metric used as a surrogate for fuel consumption was the input mechanical flow power, and the benefit was quantified by back-to-back comparison of non-BLI (podded) and BLI (integrated) configurations. The first method (indirect) was the estimate of mechanical flow power based on the measured electrical power to the propulsors, plus supporting experiments to characterize the efficiencies of the fans and the electric motors that drive them, at the MIT Gas Turbine Laboratory. The second method (direct) was the direct integration of flowfield measurements, from five-hole probe surveys at the inlet and exit of the propulsors, which provided flow angles, velocity components, and pressure coefficients. Data were taken at different wind tunnel speeds, and conditions to determine overall performance dependence on non-dimensional power and angle of attack. At the simulated cruise point, the first method gave a measured aerodynamic BLI benefit of 7.9% +/- 1.5% at 70 mph tunnel velocity, and 8.5% +/- 1.5% at 84 mph, and the second method gave a measured benefit of 8.1% +/- 3.3% at 70 mph, and 12.2% +/- 3.4% at 84 mph. For the aircraft models examined, the aerodynamic benefit was found to come primarily from a decrease in the propulsor jet velocity (increase in propulsive efficiency) and thus a decreased jet dissipation, with the contribution from decreased wake and airframe dissipation being roughly an order of magnitude smaller.