In all rotorcraft, the main rotor is the primary source of helicopter vibration, transmitting aerodynamic and inertial loads to the fuselage at a frequency proportional to the rotor speed. However, simulation of progressive immersion into an idealised sharp-edged gust induces a split around this frequency proportional to the relative velocity between gust and aircraft. To test for this effect in more complicated gust patterns, a realistic operational flowfield was generated using a computational fluid dynamics package. Numerical experiments suggest that a realistic atmospheric environment can be found which induces this split about the fundamental forcing frequency. A simple mathematical expression is derived which also predicts changes in frequency as a function of flight condition. The sensitivity of a class of optimal frequency-tuned active vibration control algorithms (higher harmonic control), to this type of disturbance is found to be poor. Enhancements to the algorithm through the inclusion of a Kalman state estimator and multi-harmonic inputs fail to yield any performance improvement. A novel modification to the algorithm allowing for direct feed forward of a Fourier estimate of the gust is shown to significantly improve controller performance. However accurately estimating the disturbance vector significantly complicates implementation of the technique.
Helicopter vibration induced by highly structured turbulence
Anregung mechanischer Schwingungen eines Helikopters durch hochgradig strukturierte Turbulenz
Journal of the American Helicopter Society ; 48 , 4 ; 244-252
2003
9 Seiten, 12 Bilder, 1 Tabelle, 22 Quellen
Aufsatz (Zeitschrift)
Englisch
Diskontinuität , Fourier-Analyse , Frequenzverschiebung , Hubschrauber , Kalman-Filter , mechanische Schwingung , numerische Strömungssimulation , Oberschwingung , pulsierende Strömung , Regelungsmodell , Rotor (Drehflügel) , Schwingungsanregung , Schwingungsfrequenz , Schwingungsregelung , Turbulenz , unstetige Strömung , Windverteilung , Zustandsschätzung , Zustandsvektor , Schwingungsbegrenzung
Helicopter Vibration Induced by Highly Structured Turbulence
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