The Reduction of Rotorcraft Power and Vibration Using Optimally Controlled Active Gurney Flap

Open Access
Author:
Bae, Eui Sung
Graduate Program:
Aerospace Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
November 02, 2012
Committee Members:
  • Farhan Gandhi, Dissertation Advisor
  • Edward A Smith, Committee Member
  • Mark David Maughmer, Committee Member
  • Christopher Rahn, Committee Member
  • George A Lesieutre, Committee Member
Keywords:
  • Rotorcraft
  • Performnce Improvement
  • vibration Reduction
  • Gurney flap
  • MiTEs
  • microflap
  • vibration
  • power
Abstract:
The main topic of the present study is the application of active control scheme for the reduction of rotorcraft main rotor power reduction and vibratory load. When the helicopter is operated near its flight boundary, the required power and vibratory loads rapidly increases which impose a limit on the helicopter operation. Various methods were proposed and studied in order to achieve performance improvement under such operating condition. The effect of active control scheme was examined for its impact on the performance improvement and vibration reduction in the present study. Numerical simulations are based on the UH-60A Blackhawk helicopter with an active Gurney flap spanning from 70$\%R$ to 80$\%R$ of the main rotor. For obtaining the aeroelastic response of the rotor blade, finite element method was used to represent elastic blade. The aerodynamic loads acting on the blade are provided by CFD based 2D lookup table. Prescribed wake model was used to resolve the induced inflow over the rotor disk. The unsteady aerodynamic behavior due to the higher harmonic actuation of active Gurney flap was resolved by the time-domain unsteady aerodynamic model. The first part of preliminary study covers parametric study using Gurney flap. Starting with simple rigid blade representation of the rotor blade, the effect of 1/rev Gurney flap actuation was examined on three different gross weights. The effect of active Gurney flap width, the chordwise location of active Gurney flap, the effect of unsteady aerodynamic model, and the effect of 2/rev actuation frequency were examined. The second part of preliminary study was conducted with the elastic blade model to include the effect of torsion dynamics. Performance improvement using active Gurney flap was examined for maximizing thrust capability at two flight speeds. 1/rev Gurney flap actuation increased the gross weight capability up to 1,000 lbs. Also, 1/rev actuation of Gurney flap increased maximum altitude limit of baseline rotor by 1,400 ft. Furthermore, it was predicted that the maximum level flight speed can be increased by 30 knots with respect to that of the baseline rotor. The effect of active Gurney flap on the vibration reduction was first examined at the stall condition. Using 1/rev actuation, in-plane vibratory force and moment can be reduced by 68$\%$ and 44$\%$, respectively. The effects of higher harmonic frequencies were investigated at the high-speed cruise speed, and single frequency phase sweep was conducted to find the best phase angle that minimizes each vibratory components. 3/rev actuation yielded 36$\%$ reduction in in-plane vibratory moment. 74$\%$ reduction in vertical vibratory force was predicted with 4/rev actuation. With 5/rev actuation, 81$\%$ reduction in vertical vibratory load was observed. With the input-output information obtained from single frequency phase sweep, the plant model which correlates active control inputs to helicopter vibratory loads was constructed. Multicyclic controller was applied to the plant model, and 25$\%$ reduction in the cost function was reported. Vertical vibratory load was reduced by 51$\%$, and inplane force and moment were reduced by 18$\%$, 22$\%$, respectively.