Experimental Investigation of the Rear-Body Aerodynamics of a Helicopter Fuselage

• Author / Creator

  Gingras, Drew R.

• Helicopters have proven to be a versatile air vehicle in today’s society and are used in a variety of applications. Many complexities arise in the aerodynamics of helicopters due to the presence of the main rotor downwash and the diverse range of flight conditions. The various uses of helicopters result in large variations in the aerodynamic loading, which can be problematic to safe flight operation.
  An experimental setup was developed in the University of Alberta wind tunnel to analyze and improve the aerodynamic performance of a helicopter fuselage under a wide array of flight conditions. The experimental model was comprised of a 3D printed fuselage equipped with a motorized main rotor used to emulate the downwash. A six-axis load cell was used to measure the aerodynamic forces and moments acting on the fuselage. Stereoscopic and multiple-camera planar particle image velocimetry (PIV) techniques were used to analyze the development of the separation bubble in the rear-fuselage wake.
  The forward flight condition was analyzed over an angle-of-attack range of -15° ≤ α ≤ 15° at zero side-slip. The drag force coefficients had the largest magnitude and decreased as the angle-of-attack was swept from positive to negative, while the lift force coefficients showed a linear increase over the same range. A down-force was present over for -15° ≤ α ≤ 5° while positive lift was noticed for 5° ≤ α ≤ 15°. The pitch moment was the only moment that showed any dependency on angle-of-attack for the forward flight condition. Nose-down moments were present for -15° ≤ α ≤ 7° while nose up moments existed for 7° ≤ α ≤ 15°.
  The level flight condition was analyzed over the side-slip angles of 0° ≤ β ≤ 180° at zero angle-of-attack. The aerodynamic forces were found to have much larger magnitudes at high side-slip relative to the forces measured in the forward flight condition. Drag and side force coefficients were shown to have significant variation with changing side-slip. The drag increased to a maximum value occurring at β = 80°. The side force coefficients were positive for 0° ≤ β ≤ 100° and before transitioning to negative magnitudes for 100° ≤ β ≤ 180°. The lift force coefficients showed small fluctuations around a magnitude of zero. The dominant moment acting on the fuselage was in the yawing direction, which is countered by the tail rotor. The roll moments showed a near linear increase for 0° ≤ β ≤ 90° before decreasing back to zero over 90° ≤ β ≤ 180°. The pitch moment coefficients showed large changes in magnitude, particularly from β = 20 ° to 30° and from β = 60 ° to 70°. These large magnitude variations draw concern for safe flight operation.
  Stereo and multiple-camera planar PIV was used to analyze the effect of the main rotor downwash in the rear-fuselage wake. The presence of the downwash consistently resulted in a more rapid expansion of the wake, resulting in a larger separation region. The larger separation region would add to the pressure drag of the fuselage. The downwash also introduced an additional downwards component of velocity across the measurement region that resulted in a 10% increase of the mean velocity magnitude in the vertical plane of the wake.
  Four rear-fuselage designs including a removable motor geometry, streamlined casing, and round casing were developed and analyzed at side-slip angles between β = 0° and 40°. The load measurements revealed that the streamlined case achieved up to 20% drag reduction over 0° ≤ β ≤ 30°, while the round case increased the drag by up to 18% for 0° ≤ β ≤ 40°. The magnitude of the pitch moment variation between β = 20° and 30° was reduced by 36% and 67% using the streamlined and round cases respectively.
  A four-camera planar PIV campaign was performed to investigate the effect of the four rear-fuselage geometries on the wake for side-slip angles of 0° ≤ β ≤ 40°. The streamlined case was found to consistently reduce the size of the separation bubble, thus explaining the reduced drag. Sharp flow separation points were noticed to cause large regions of high velocity fluctuations. The constant aft-body curvature of the rounded case reduced the effects of the sharp separation point, resulting in less abrupt changes in the aerodynamic forces and moments for changing side-slip angle.

• Subjects / Keywords

  • Aerodynamics
  • Helicopters

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Master of Science

• DOI

  https://doi.org/10.7939/R3X34N756

• License

  Permission is hereby granted to the University of Alberta Libraries to reproduce single copies of this thesis and to lend or sell such copies for private, scholarly or scientific research purposes only. Where the thesis is converted to, or otherwise made available in digital form, the University of Alberta will advise potential users of the thesis of these terms. The author reserves all other publication and other rights in association with the copyright in the thesis and, except as herein before provided, neither the thesis nor any substantial portion thereof may be printed or otherwise reproduced in any material form whatsoever without the author's prior written permission.