A slotted tip was developed to modify the characteristics of the strong vortex trailed from the tip of a small-scale helicopter blade. Forward-facing slots directed a slight amount of the incident flow in the spanwise direction, which was vented at the side edge of the blade tip. This caused the tip vortex to detach from the blade tip face, and also introduced turbulent vortlets into the laminar core of the developing vortex. The resulting wake flowfield was investigated using flow visualization and laser Doppler velocimetry. Measurements were conducted to quantify the vortex swirl velocity components, the inner core development, and the overall vortical flow inside the vortex trails. The results were then compared to a baseline blade with a standard unmodified rectangular tip. It was found that the slotted blade reduced the peak value of the swirl velocity components in the tip vortex by up to 60% relative to those of the baseline blade. The core growth of the tip vortices from the slotted blade suggested a much higher rate of diffusion, up to as much as three times that of the baseline case. Measurements of rotor power showed only a 3% increase relative to the baseline tip. Based on the overall results, the slotted blade is considered a highly effective design in diffusing vorticity and reducing the flow high field velocities that would otherwise be induced by a rotor tip vortex.
Investigation of helicopter rotor-blade-tip-vortex alleviation using a slotted tip
Schwächung des Spitzenwirbels an einem Hubschrauberrotor durch an der Flügelspitze ausströmende Luft
AIAA Journal ; 42 , 3 ; 524-535
2004
12 Seiten, 13 Bilder, 2 Tabellen, 34 Quellen
Aufsatz (Zeitschrift)
Englisch
Ausflussströmung , Diffusionsströmung , Drallströmung , Geschwindigkeitsprofil , Hubschrauber , Laser-Doppler-Anemometrie , Leistungsbedarf , Loch (Öffnung) , Nebenstromkanal , Radius , Rotor (Drehflügel) , Strömungsgeschwindigkeit , Strömungsumlenkung , Visualisierung , Wirbel (Strömung) , Wirbelkern , Wirbelstärke , Zirkulation
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