CHARACTERISTICS OF A ROTOR OPTIMIZED FOR HOVER AND FORWARD FLIGHT

Open Access
Author:
Kroninger, Christopher Matthew
Graduate Program:
Aerospace Engineering
Degree:
Master of Science
Document Type:
Master Thesis
Date of Defense:
None
Committee Members:
  • Farhan Gandhi, Thesis Advisor
Keywords:
  • circulation
  • optimization
  • rotorcraft
Abstract:
A methodology has been implemented to minimize the total power consumption of a rigid hingeless rotor. The baseline rotor has a 20ft radius with both 10% root cutout and blade solidity and operates at a CT of 0.007 in hover. The rotor is optimized at five advance ratios, 0.0, 0.1, 0.2, 0.3, and 0.4. A free wake model is developed with a lifting line to model the wing. The input of the code can be either the desired circulation or pitch distribution. A gradient based optimizer built around the free wake analysis allows the distribution to be modified at 15 radial by 36 azimuthal elements. A perturbation contour is added to the original distribution to obtain an improved distribution and then a new perturbation contour is found in an iterative process. This process repeats until the change in power is less than one percent for a given perturbation contour. The resulting optimized contours yield savings in hover of 30.0% with more modest gains of a few percentage points in forward flight. The main source of power savings is a reduction in induced power at all speeds. The lift distributions tended to move lift production inboard although this would be accomplished in different regions of the disk depending on the flight speed. The optimized solutions also responded to sharp and discrete features in the wake. Effects of trailing vortices near the disk can be seen in the downwash and the optimized twist distribution seeks to follow these features. The lift and twist distributions vary with significant non-linearity both radially and azimuthally. There is also little coherence radially between the magnitude and phase of respective harmonics composing these distributions.