Powered Wing Response to Streamwise Gust Encounters

Date of Award

5-5-2024

Degree Name

M.S. in Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Sidaard Gunasekaran

Abstract

Recent advancements in battery technology have led to an increase in the development of electric Vertical Takeoff and Landing (eVTOL) vehicles, typically using electrically-powered propellers to generate both lift and thrust. These vehicles typically operate in low-altitude, and limited-space conditions in urban environments. Unsteady flows from building wakes or atmospheric boundary layer effects raise concern to the stability of eVTOL-capable aircraft under normal operating conditions and during transition from vertical to forward flight and vice-versa in population dense areas. Although all types of unsteady flows have been studied for decades, little has been published on the influence of unsteady flow on a propeller-wing system. Understanding of this system is crucial to ensuring the safety of not only the passengers of these VTOL aircraft, but also the safety of the public. Investigation into powered wing response to streamwise gust encounters was conducted through various propeller locations, angles of attack, reduced frequencies, and thrust levels. All experiments were run at the University of Dayton Low Speed Wind Tunnel (UD-LSWT) in its open-jet configuration. The shuttering system downstream of the test section consists of a set of rotating louvers that change angle to effectively change the blockage ratio of the wind tunnel. Different louver angles and actuation frequencies provide different velocities and reduced frequencies. Particle Image Velocimetry (PIV) was conducted on the freestream flow during actuation of the louvers to spatially characterize the angle of attack variation throughout the test section. The results from PIV were used to determine the optimal testing location and wing size for the test article. The wing was designed to be modular, accepting a number of different propeller Distribution Statement A: Approved for Public Release; Distribution is Unlimited. PA# AFRL-2024-2083 4 locations. Four total configurations were considered – unpowered, midspan, semi-midspan, and wingtip. Each configuration was tested through the entire reduced frequency regime, from steady and quasi-steady to high unsteady flow. Extended analysis provided interesting conclusions about the interconnected effects of each parameter varied through the experiments. Angle of attack and thrust had significant impact in the lift response of the wing in addition to the various trends that occur at the different reduced frequencies. The addition of a propeller lowered the threshold for unsteady behavior, especially at high angles of attack and high thrust. The steady state thrust affects the peak ���� achieved in unsteady flow in a linear fashion. Strategic propeller placement at the midspan, where the unpowered wing is prone to flow separation, can completely eliminate stall and achieve a higher peak ���� compared to other configurations. Various transitional flight profiles with discrete streamwise gusts were designed and implemented on the configurations mentioned previously.

Keywords

unsteady aerodynamics, propeller-wing system, aerodynamics, gust response, streamwise gust, longitudinal gust, powered wing

Rights Statement

Copyright 2024, author

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