An Aerodynamic Analysis of a Singlebladed Rotor in Hovering and Low- Speed Forward Flight as Determined From Smoke Studies of the Vorticity Distribution in the Wake

Abstract

= "».• " "»/«o« iracber of helical vortex filaments used to approximate the vortex sheet In hovering flight •a-»«" manber of vortex filaments approximating vortex sheet in forward flight analysis radius of helical tip vortex, ft. radial distance from helix axis of any point at vhich the Induced velocities are desired, ft. radial position of vortex filaments as defined by eq. A-53> ft. radius of point (X/yO on helix from wake axis (^-axis), ft. radius of r^tor, ft. pop-d 1 mensional induced velocities associated with tip vortex non-dimensional induced velocities associated with vortex sheet in forwari flight time, measured from »o , sec. time required for wake to reach steady configuration, sec. rotor thrust, lbs. rtdial velocity component associated with vortex sheet in forward flight, ft/sec. radial induced velocity associated with lifting line, ft/sec. radial induced velocity associated with tip vortex, ft/eec. \uan*m T ~ " "-wij<..i...wt».-^A-JJU»^ ■ ."■ ■ * i^g.rf ^c' i'ii' 1 n ii 1 i>iiiiyrigiBrjiwiij'ii3tii'i

An Analytical and Experimental Investigation of Helicopter Rotor Hover Performance and Wake Geometry Characteristics

“…reasing number of blades, blwde loading, and tip Mach number. In addition, 3 tendency for improved agreement with increased blade twist was noted with the models.…”

“…Perhaps a we dramatic example of the instability is presented in the series of Figu. 3 30, in which the fourth vortex cross section moves radially out and eventually to the side of the third. Although it is recognized that a small perturbation such as a small amount of ambient wind or a slight blade-out-of-track may be necessary to precipitate the instability, this is believed to be an academic consideration since full-scale rotor operation is certainly subject to greater disturbances than those present wnder the laboratory conditions of this investigation.…”

Flow Visualizations and Extended Thrust Time Histories of Rotor Vortex Wakes in Descent

“…In view of the acute effect the wake has on the rotor performance, researchers began to undertake more detailed experimental studies of the wake flow field, beginning with wind tunnel testing and smoke flow visualization as early as the 1920s (Refs. 7,13,14). Later, experiments were done using hot wire anemometry (HWA) and other techniques (Ref.…”

Large-eddy simulation of impinging jets on smooth and rough surfaces

“…This flow field is complex in structure: the coherent helical vortices generated at the rotor-tip and the vortex sheet generated by the inner part of the blade are embedded into the jet. [1] If the rotor forms an angle to the horizontal plane, further complexity occurs. [2] A laboratory-scale visualisation of this flow field is shown in Figure 1(a).…”