Wakes of lifting propellers (rotors) in ground effect: final report
The report presents the development of a wake model for a lifting propeller (rotor) in ground effect and the computational procedure used to determine the spacial distribution of wake vorticity and the induced velocity field accompanying that vorticity distribution. Sample calculations for a two-bladed rotor were carried out on an IBM 7044 computer. Locations of wake vortical elements and the associated induced velocities at selected field points are presented for advance ratios of 0, 0.02, 0.05, and 0.10 for an H/R (ratio of rotor height above ground to rotor radius) of 1.0. Also, a few results for a hovering case with H/R = 0.5 are presented. A calculated root-mean-square velocity map is compared with measured hovering data (time averaged) and good agreement is obtained in the outer half of the slipstream. The implications of computed results with respect to the flow field at a horizontal stabilizer or tail rotor are noted as examples of the use of the model. The wake vortex model used for these calculations is a distorted continuous helix emanating from each blade tip. (Author).
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GENESIS OF THE IDEALIZED MODEL
RESULTS OF SAMPLE COMPUTATIONS
2 other sections not shown
actuator advance ratio azimuth position blade bound vortex Blade Number blade vortex boundary circulation computer program coordinates core diameter CORE LOCATIONS Cornell Aeronautical Laboratory Crimi degrees Figure Equation Fixed Field Points FIXED POINTS flow field fluid FUSELAGE LOCATION ground effect ground plane Helicopter Rotor HELIX MODEL HELIX SOLUTIONS hovering induced velocity LIFTING PROPELLERS ROTORS LINE OF LOCATION loading parameter LOCATION OF FIXED LOCATION VS REFERENCE Longitudinal Plane measurements Naval Research Navy Washington NONDI Nondimensional Velocities NXPT obtained ONAL VELOCITIES Plane of Symmetry Plane vs Reference Positions of Wake radial radial velocity Reference Blade Position RING AND HELIX roll-up rotor blade rotor radius self-induced velocity shown in Figure slipstream SPONSORING MILITARY Symmetry When Blade Tip Path Plane variable variations VELOCITIES ALONG GROUND Velocities at Fixed velocity field velocity time histories vortex element VORTEX RING vortex tube Wake Vorticity Cores Wright-Patterson AFB zero