Session: 01-04: Inlet Distortion and Engine Operability

Submission Number: 175298

Applying Boundary Layer Ingestion to Electric Drone Propulsion 

The benefits of electrification and hybridization can be better realized when combined with aircraft architectures and layouts to benefit from Boundary Layer Ingestion (BLI) for reducing the overall aircraft energy consumption. The concept of BLI originates from marine propulsion, where ship propellers are installed at the stern to energize the slow-moving boundary layer flow near the vessel’s hull, generating thrust. This energy recovery principle is also applicable to aircraft. In a typical commercial aircraft cruising at altitude, the fuselage boundary layer contributes roughly 30–35% of the total aerodynamic drag. By ingesting this boundary layer, the overall drag can potentially be reduced. This approach can also lower the power needed to generate the same amount of thrust, resulting in improved propulsive efficiency. According to literature, power savings range from 5 to 13%, with fuel burn reductions between 12 and 36%.

Among the various BLI architectures, the aft-mounted fan design (also known as a tail cone thruster or propulsive fuselage) is considered one of the most promising in terms of enhancing propulsive efficiency. Its nearly axisymmetric inflow reduces unsteady fan blade loading, and the fan design can be optimized to minimize installation penalties. Furthermore, the aft-mounted fan more closely resembles conventional aircraft designs, which helps de-risk the design, analysis, and certification processes compared to more radically unconventional configurations. Although BLI has been studied for a decade as a means to improve aircraft propulsive efficiency, the results to date remain insufficiently quantified and validated, necessitating further experimental investigation. Thus far, the experimental studies have focused on small-scale experiments for only the propulsion system and have not yet been applied to a full aircraft.

The current collaborative research project between the National Research Council Canada (NRC), the University of Alberta (UofA), and UVA Dynamics Inc. (UVAD) aims to integrate a customized BLI propulsion unit into the tail of a medium-sized UAV. It aims at improving propulsive efficiency, reducing drag, and lowering power consumption and battery size by experimentally validating BLI technology on UAVs, a first in this application. This proof-of-concept work addresses knowledge gaps with dedicated numerical analysis and wind tunnel testing to mitigate risks before potentially applying BLI to larger, human-piloted aircraft.

In this paper, high-fidelity CFD analyses were performed to investigate the baseline UAV configuration, and to evaluate the potential benefits of the BLI concept. This involved grid generation and flow simulations on the baseline model, incorporating various propeller configurations, and assessing the impact of BLI on overall drag reduction. The next phase of the project will focus on the design, fabrication, and execution of experimental testing, which will take place in the NRC’s 2 m × 3 m wind tunnel.

The numerical simulations were validated against experimental data obtained from tests on the model without a propeller. CFD results indicate that drag reduction via BLI is highly dependent on the propeller’s size relative to the incoming boundary layer and its aerodynamic performance across varying airspeeds and rotational speeds. Overall, the drag reductions indicated by the CFD results were modest, ranging from 0.1 to 2.5 N (6 to 19%), highlighting the need for precise load cell selection in the experimental setup to accurately capture these subtle force differences. The enhanced propulsive efficiency will be measured following experimental testing.  

Presenting Author: Faezeh Rasimarzabadi National Research Council Canada

Presenting Author Biography: Dr. Faezeh Rasimarzabadi holds a Ph.D. in Aerospace Engineering and completed her Post-Doctoral research in Mechanical Engineering at the University of Alberta. She is currently a Senior Research Officer at the Aerospace Research Centre of the National Research Council Canada, working within the Propulsion and Power Laboratory. Her research primarily focuses on advancing hybrid electric aircraft technologies, including the development and validation of novel airframe-engine configurations and thermal management systems.

Authors:

Faezeh Rasimarzabadi National Research Council Canada
Philip Mccarthy National Research Council Canada
Blair Jensen UVA Dynamics Inc.
Alex Li UVA Dynamics Inc.
Dale Mckay UVA Dynamics Inc.
Arno Claassens University of Alberta
Dylan Hilman University of Alberta
Sina Ghaemi University of Alberta