Measurement Around A Rotor Blade Excited In Pitch, Part 1: Dynamic Inflow.
Shiuh-Guang Liou, Narayanan Komerath, Mihir Kumar Lal .
Journal of the American Helicopter Society, Vol. 39, No. 2, April 1994,
Abstract: This is the first of two papers describing experiments on a two-bladed
rotor in hover, under controlled pitch excitation. Measurements of the inflow
to the rotor are described, first under steady conditions, and then under
prescribed 4-per-rev pitch excitation. The high data rates, data acquisition
techniques and data quality required for this experiment are demonstrated,
including 4-per-rev velocity variations due to 1-degree pitch oscillation,
extracted over a single period of rotor revolution at 600rpm. The steady
case results agree with lifting-line-based analytical predictions except
in the tip region, as expected. The excited-blade case shows the 4-per rev
velocity perturbation, and the dependence on the phase of the excitation.
Spectral analysis of the LDV data shows multiple harmonics of the excitation
frequency. The rate of pitch change is seen to be high enough to produce
substantial hysteresis effects, whose variation with radial position is
measured. The hysteresis is seen to arise from the inboard shed vorticity,
and to decay towards the tip.