Aerodynamic Investigation of an Over-the-Wing Propeller for Distributed Propulsion

Abstract

This paper addresses the aerodynamic performance and numerical modeling of overthe-wing propellers. Installing the propeller above a wing has the potential to increase wing lift-to-drag ratio, high-lift capabilities, and to reduce flyover noise. However, the prediction of its performance is difficult, since research on the aerodynamic interaction effects of over-the-wing propellers has been limited so far. For this reason, an exploratory wind tunnel campaign was performed with a wing featuring a fowler flap. A single propeller was installed above the wing at different chordwise locations and inclination angles. Wing surface-pressure and wake-pressure measurements showed strong, bilateral aerodynamic coupling between the propeller and wing. A configuration with the propeller attached to the flap showed wing lift increases of 8% and 3% in cruise and high-lift conditions, respectively. The key findings of the wind tunnel campaign were used to validate a low-fidelity numerical tool, which combines a non-uniform inflow blade-element model for the propeller, a panel method for the wing, and a vortex lattice model for the propeller slipstream. The numerical model was used to assess the effect of propeller axial location and diameter. Results indicated that the optimal axial propeller position is near the trailing edge of the wing, and that reducing the propeller diameter at constant thrust coefficient at this location is beneficial for distributed propulsion applications. The tool allows a rapid computation of over-the-wing propeller and wing performance in cruise conditions. This enables an efficient design space exploration during the conceptual design process of such configurations.

Aero-Propulsive Efficiency Requirements for Turboelectric Transport Aircraft

“…The leading-edge propellers can increase the maximum lift coefficient of the wing [32], leading to a significant increase in wing loading [23,38]. Over-the-wing propulsion, meanwhile, increases the lift-to-drag ratio of the wing [33]. Finally, the use of boundary-layer ingestion affects airframe drag and increases the thrust-to-power ratio of the rear propulsor [34,39], which, from a preliminary sizing perspective, can be modeled as an change in propulsive efficiency and drag coefficient.…”

“…And secondly because, even though several turboelectric aircraft design studies have been performed [13,18,30,31], there is still a large uncertainty regarding the benefits of such aircraft, especially due to the lack of propulsion-airframe integration studies. While the aerodynamic benefits of novel propulsion-system layouts such as leading-edge distributed propulsion [32], over-the-wing propulsion [33], under-the-wing propulsion [13], boundary-layer ingestion [34], or tip-mounted propulsion [35] have been studied at subsystem level, it is still unclear which of these configurations leads to the greatest benefit at aircraft level. Although such propulsion systems do not necessarily need a hybrid-electric powertrain [36], many radical aircraft configurations with improved propulsion-airframe integration are only viable when combined with HEP, and thus the overall benefit is highly dependent on the maturity of the powertrain components [37].…”

A Review of Concepts, Benefits, and Challenges for Future Electrical Propulsion-Based Aircraft

“…The propulsors can be spread in multiple fashions, such as in the leading edge of the wing [56,57], over-the-wing [58][59][60], under-the-wing [59,61], on the wing-tip [57,62], and on the fuselage-aft [26,53,63] to realize aero-propulsive synergistic integration benefits. Such benefits can be materialized in multiple ways: a lower size wing, better cruise performance, a shorter take-off and landing length etc.…”

An Investigation of the Aerodynamic Performance for a Fuel Saving Double Channel Wing Configuration

“…For the purpose of utilizing the suction effect ahead of the propeller, it is better that the propeller is placed above the wing, which is called over-the-wing (OTW) propeller configuration [25][26][27]. The experimental result demonstrates that the OTW configuration has an excellent advantage of reducing the wing drag through the propeller blade suction compared with a tractor propeller arrangement, while its lift enhancing capability is slightly weaker than the latter.…”