Benefits of Boundary Layer Ingestion Propulsion

This paper presents experimental measurements of propulsive power reduction due to boundary layer ingestion, for an electric ducted fan propulsor behind a NACA 0040 body of revolution at a Reynolds number of approximately 240,000. The propulsive power is defined as the electrical power required by the propulsor to obtain a zero net streamwise force on the body/propulsor combination, mimicking the cruise condition for an aircraft. The benefits of the boundary layer ingestion are quantified as a power saving coefficient, or ratio relative to the no-ingestion case where the propulsor is isolated from the wake. The measurements show a maximum power savings when the propulsor is closest to the body centered on the body axis, with savings of 26% for an untripped flow case and 29% for a tripped flow case. A second iteration of experiments were performed, showing a maximum power savings of 25% for a tripped flow case. Propulsor locations farther downstream and further off-axis show progressively smaller power saving benefits. An uncertainty analysis is performed to verify the measurements to within 99% confidence. Wake profiles were also measured to confirm that the wake was fully ingested for on-axis propulsor locations.