Title

Changes in Propeller Performance Due to Ground and Partial Ground Proximity

Author

Jielong Cai

Date of Award

1-1-2020

Degree Name

M.S. in Aerospace Engineering

Department

Department of Mechanical and Aerospace Engineering and Renewable and Clean Energy

Advisor/Chair

Advisor: Sidaard Gunasekaran

Abstract

With the increased usage of propeller-driven unmanned-aerial-vehicles (UAV) in closed spaces such as caves, buildings, pipelines, etc. for photography, surveillance, and inspection, understanding the influence of the ground and ceiling on a remote-controlled (R/C) propeller is of the utmost importance. The flying characteristics of drones changes when an object or a ground plane is in its close proximity due to changes in its propeller performance. The changes in performance are due to the changes in the flow field around the propeller that occur due to ground proximity, which is also known as ground effect.Ground effect on lifting rotor performance has been studied theoretically and experimentally for decades. Historically, most investigations focus on helicopter rotors, which have high aspect ratio, lower pitch and rarely have spanwise twist. This research focuses on smaller size rotors, in particular, the thin-electric propeller which is used widely on small UAVs. The research considers parameter variations not broadly available in the literature such as propeller pitch, diameter, solidity, and blockage. In particular, extreme ground effect is considered, where the ratio of ground plane stand-off distance to propeller diameter is 0.1 or less. Moreover, the propeller is reversed, to examine the ceiling effect. Typically, the ground effect investigation is done with a ground plane that is big enough to be considered an infinite plane. In this research, both infinite plane and circular plates of similar diameter (or less) of the propeller are used as ground planes. Various circular plates with different diameter to propeller diameter ratios are used in the research representing different `blockage ratios'. The investigation gives insight into changes in propeller performance in proximity to fuselages of a given diameter in propeller-driven airplanes under pusher and puller configurations. All experiments were conducted on a thrust-stand built in-house at the University of Dayton Low-Speed Wind Tunnel (UD-LSWT) Laboratory. All propellers used in the experiment are from the "thin electric" APC series, with diameter ranging from 11 inches to 17 inches and pitch from 4.5 inches to 14 inches. The propeller peak Reynolds number varies from 90,000 to 190,000 in the experiment. Circular plates with diameter ratio from 0.5 to 1.0 are used in the blockage effect experiment. Force, torque and RPM propeller data are taken during the experiment from a propeller diameter normalized ground distance of -1.5 to 1.5. Results from the infinite ground experiment are separated into three major sections: thrust coefficient and power coefficient, power required at constant thrust, and effective thrust. A significant increment in the thrust coefficient and decrement in the power coefficient is found in ground proximity among the propellers with a pitch-to-diameter ratio less than 0.7. This results in a decrement of power required at constant thrust in ground effect. Almost identical changes in the power required at constant thrust in the ceiling effect is also found in most of the low pitch to diameter ratio propellers. For the blockage experiment, a less significant reduction in the power required in constant thrust for all propellers is found at lower blockage ratios as expected. Similar trends in the effect on? thrust for different propellers at the same blockage ratio are found. Results for the positive h/D region (the puller configuration), overlap regardless of the propeller pitch to diameter ratio or solidity. A phenomenological expression (an algebraic equation) for power required at constant thrust as a function of propeller parameter is established during the research to predict the changes in the propeller performance in ground effect which will benefit the operation of small UAVs in both open and confined areas.

Keywords

Aerospace Engineering, Propeller aerodynamics, Ground effect, Partial ground effect, Ceiling effect

Rights Statement

Copyright 2020, author

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