Session: 01-04 Inlets, Ducts & BLI

Paper Number: 82472

82472 - Impact of Boundary Layer Ingestion on the Performance of Propeller Systems for Hybrid Electric Aircraft 

Boundary layer ingestion (BLI) constitutes a propulsion configuration with demonstrated potential for reduced thrust requirements and therefore, reduced fuel consumption and environmental impact. The theoretical aerodynamic benefits are often outperformed by weight penalties associated with the integration or addition of propulsors into the airframe. Future designs for commuter and regional aircraft include aft-fuselage-mounted propellers which are ingesting part of the airframe boundary layer. Considering mid-term timeframes, BLI propellers are typically powered by hybrid electric power systems. This work sheds light into the impact of BLI on the performance of electrified propeller-driven propulsion systems for small aircraft.

A rotor model is employed based on lifting line theory allowing arbitrary radially varying inflow velocity profiles. A semi-rigid wake representation is adopted for the calculation of rotor self-induced flow. A high-order, two-dimensional panel method is utilized for modelling the flowfield around the fuselage. An integral boundary layer formulation is used for the estimation of boundary layer thickness and a semi-empirical formulation for the approximation of boundary layer profile. The individual modules are coupled within a computational scheme for the rapid evaluation of propeller aerodynamics including the effects of blade design and propulsion installation. The impact of BLI on propeller performance maps is quantified, with efficiencies up to 15% higher compared to a propeller in uniform freestream conditions.

A design space exploration framework is developed for the analysis of BLI effects at propulsor system level, including the impact of weight differentiation, installation technology factors, thrust split between rotors and electrical transmission losses. A reference 19-passenger commuter aircraft featuring two wing-mounter tractor propellers is compared with a series of conceptual designs featuring an aft-fuselage-mounted BLI propeller and two wing-mounted tractor propellers. In each conceptual configuration, the propellers are re-sized based on the disk loading of the reference aircraft to ensure consistent comparisons. A system-wide power saving coefficient is derived for the quantification of performance deltas between the conceptual and the reference system, including all propulsors. For systems with BLI aerodynamic benefits entirely outperformed by weight penalties, and electrical power transmission losses of 10%, a power saving coefficient of 1.5% is accrued for the conceptual configuration relative to the reference aircraft. In a technologically advanced system with 2% thrust benefit due to BLI and 3% electrical transmission losses, power savings rise to 6.5%.

This paper provides insight into the tradeoffs governing the sizing of BLI propeller systems at conceptual design stages. The developed methodology enables the multi-parameter evaluation of propeller systems throughout the feasible design space. The outcomes of design space exploration establish design guidelines for the detailed aerodynamic analysis of the optimal configurations. Finally, this work identifies the maximum potential as well as the limitations of BLI propulsion for the small aircraft of the future.

Presenting Author: Stavros Vouros Mälardalen University

Presenting Author Biography: Post-Doctoral Researcher in Energy and Environmental Engineering within the Future Energy Center of Mälardalen University (Sweden). PhD on the “Aeroacoustic Simulation of Rotorcraft Propulsion Systems” from Cranfield University (UK). Five-year Engineering Diploma (Dipl.-Ing.) from the Aristotle University of Thessaloniki (Greece), focused on turbomachinery and experimental fluid mechanics. More than seven years of experience in academic and institutional research within industrial-, state- and EU-funded projects. Scientific and teaching interests include modelling and control of energy systems, artificial intelligence, optimization, novel propulsion systems, computational aeroacoustics, aerodynamics and experimental fluid mechanics.

Authors:

David Hiebl Mälardalen University
Stavros Vouros Mälardalen University
Konstantinos Kyprianidis Mälardalen University