Accession Number : ADA135555

Title :   Helicopter Rotor Wake Geometry and Its Influence in Forward Flight. Volume 1. Generalized Wake Geometry and Wake Effect on Rotor Airloads and Performance.

Descriptive Note : Contractor rept.,


Personal Author(s) : Egolf,T A ; Landgrebe,A J

PDF Url : ADA135555

Report Date : Oct 1983

Pagination or Media Count : 218

Abstract : An analytic investigation to generalize wake geometry of a helicopter rotor in steady level forward flight and to demonstrate the influence of wake deformation in the prediction of rotor airloads and performance is described. Volume 1 presents a first level generalized wake model based on theoretically predicted tip vortex geometries for a selected representative blade design. The tip vortex distortions are generalized in equation form as displacements from the classical undistorted tip vortex geometry in terms of vortex age, blade azimuth, rotor advance ratio, thrust coefficient, and number of blades. These equations were programmed to provide distorted wake coordinates at very low cost for use in rotor airflow and airloads prediction analyses. The sensitivity of predicted rotor airloads, performance, and blade bending moments to the modeling of the tip vortex distortion are demonstrated for low to moderately high advance ratios for a representative rotor and the H-34 rotor. Comparisons with H-34 rotor test data demonstrate the effects of the classical, predicted distorted, and the newly developed generalized wake models on airloads and blade bending moments. Use of distorted wake models results in the occurrence of numerous blade-vortex interactions on the forward and lateral sides of the rotor disk. The significance of these interactions is related to the number and degree of proximity to the blades of the tip vortices. The correlation obtained with the distorted wake models (generalized and predicted) is encouraging.

Descriptors :   *Wake, *Vortices, *Helicopter rotors, *Aerodynamic loading, *Rotor blades(Rotary Wings), Level flight, Air flow, Boundaries, Load distribution, Computerized simulation, Thrust, Coefficients, Mathematical prediction, Bending moments, Shape, Distortion, Mathematical models, Correlation

Subject Categories : Helicopters
      Fluid Mechanics

Distribution Statement : APPROVED FOR PUBLIC RELEASE