A time-stepping flutter analysis code was introduced, combining an unsteady, two-foil panel code with a two-degree-of-freedom spring/mass structural dynamic model for simulating inviscid, incompressible flows. The accuracy and limitations of the approach were demonstrated through comparisons with past frequency-domain studies for single-degree-of-freedom pitching motions. Computed results agreed well with the frequency-domain results. The time-stepping approach provided the additional capability to analyze the evolution of the motion in time. Qualitatively, trends in the resultant pitching frequency due to sectional thickness and moment of inertia were clearly correct, and quantitative agreement was within the expected bounds afforded by the panel method. Feedback loop algorithms were developed, and the included results demonstrated their success in simulating wake interference in rotary-wing flows, flutter in ground effect, and actively suppressing flutter. Wake interference in rotary wing flows was modeled by placing a second airfoil in appropriate distance upstream to simulate the interfering wake from the previous blade. The computed stability boundaries agreed well with past frequency domain studies. Flutter in ground effect was simulated by placing an image airfoil within the ground, moving in a mirror-image fashion. Presented results demonstrated the stabilizing effect of low-level flight and suggest that vehicles designed to fly in ground effect do so at an altitude of less than three chord lengths. For the conditions tested, it was shown that flight near a ground plane at higher altitudes promotes instability. A more extensive study of the conditions promoting stability and instability is recommended in the future. Active control simulations indicated that the controlling airfoil remains effective even with greatly reduced chord lengths, but that effectiveness was lost as the distance between the foils increased. This suggests that a closely placed canard or leading-edge flap may be sufficient for controlling flutter. The time-domain approach presented here is quite robust and efficient. Typical single airfoil simulations run in a workstation in a few minutes.
Time-domain analysis of low-speed airfoil flutter
Zeitbereichsanalyse des Tragflügelflatterns bei niedrigen Geschwindigkeiten
AIAA Journal ; 34 , 5 ; 1027-1033
1996
7 Seiten, 16 Bilder, 15 Quellen
Article (Journal)
English
Tragflügel , Flattern , inkompressible Strömung , reibungsfreie Strömung , Software , Frequenz , Kippmoment , Schwingungsdämpfung , Stabilisierung , Wirbelstraße , Strömungsvorgang , Interferenz , Aerodynamik , Algorithmus , Auftrieb , Differenzialgleichung , Rückkopplung , Trägheitsmoment , Instabilität
Time-Domain Analysis of Low-Speed Airfoil Flutter
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