Wind Tunnel Investigation of the Effect of Duct and Cross-flow on Small Propellers for Unmanned Aerial Vehicles

  • Author / Creator
    Serrano, David
  • The expanding field of unmanned aerial vehicles (UAV) has introduced a variety of flight operating conditions and thus, performance requirements. As a method to improve performance in the propulsion systems of UAVs, two topics of interest are emphasized in this thesis: the potential improvements offered by ducted propellers, and the relatively uninvestigated performance of small-scale rotors at non-zero angle-of-attack. The growing capabilities of UAVs equipped with propellers imply that rotor disks operate at a much higher angle-of-attack than in the case of helicopters or propeller powered airplanes. These two topics are the focus of this thesis, namely: the aerodynamic performance of a small ducted propeller with in axial flow condition; and the performance of small propellers at angles-of-attack ranging from 0° to 90°. The experiments were performed inside a close-loop wind tunnel facility. Load cell measurements performed at free stream velocities of 0 m/s to 15 m/s demonstrated that the four ducted propeller models tested outperformed the open propellers in thrust generation up to an advance ratio of 0.25~0.35. Inlet flow visualization using planar particle image velocimetry demonstrated that one of the reasons for the drop in performance of the ducted propeller with increasing advance ratio was a reduction in the mass flow rate through the rotor disk plane relative to the open propeller by approximately 2.5%. Flow visualization at the exit of the duct using stereoscopic particle image velocimetry revealed that the ducted propeller mitigated the contraction of the propeller jet by achieving an exit area-to-rotor disk area ratio of 1.04. In the second investigation, the performance of four 12 inch propellers was investigated at angles-of-attack ranging from 0° to 90° and free-stream advance ratios ranging from 0 to 0.55. The propellers differed in terms of airfoil section, chord length and pitch angle distribution along the span of the blade. Wind tunnel load measurements revealed that with increasing angle of attack and constant advance ratio, an increase in thrust was achieved, for constant propeller rotational velocity. Aerodynamic moments provided evidence of pitch and yaw moments generated by the non-uniform distribution of the blade angle-of-attack over the rotor disk area. An analytical performance prediction model was developed using blade element theory, where a first harmonic induced velocity model was applied. The model was adjusted using the experimentally obtained data and the Genetic Algorithm from MATLAB. The resultant model successfully predicted distributions of the effective angle-of-attack of the blade elements and of the differential thrust generated that coincided with the experimental wind tunnel data.

  • Subjects / Keywords
  • Graduation date
    Fall 2018
  • Type of Item
  • Degree
    Master of Science
  • DOI
  • License
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