The paper presents a detailed general vortex model of the unsteady aerodynamics of small perturbations about a basic axisymmetric state of hovering or axial flight. The basic state includes general distributions of circulation along the blades and general wake geometry. The perturbations are caused by small motions of the blades that are superimposed on the basic state. These motions cause small perturbations in the vorticity distribution over the lifting surfaces and in the wake. In addition, since the wake originates at the trailing edge of the blades, the small motions of the blades result in variations in the wake geometry that have an influence on the induced velocity. Moreover, variations in the locations of the blades change the distances between the vortex elements in the wake and points on the surface of the blades. These changes in the distances result in variations in the induced velocities. The two geometric effects were not included in previous unsteady models. After the presentation of the general model the case of harmonic perturbations is considered. The entire flow field is divided into near and far fields. Useful simplifications for the far field are derived. At last the case of constant circulation along the blade and radial trailing edges is presented.
A model of the unsteady aerodynamics of a hovering helicopter rotor that includes variations of the wake geometry
Ein Modell zur instationären Aerodynamik eines Hubschrauber-Rotors im Gleitflug unter Berücksichtigung von Variationen der Wirbelgeometrie
Journal of the American Helicopter Society ; 40 , 3 ; 6-16
1995
11 Seiten, 18 Quellen
Aufsatz (Zeitschrift)
Englisch
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