Accession Number : ADA294466

Title :   The Effects of Vortex Modeling on Blade-Vortex Interaction Noise Prediction,

Corporate Author : NATIONAL AERONAUTICS AND SPACE ADMINISTRATION MOFFETT FIELD CA AMES RESEARCH CENTER

Personal Author(s) : Gallman, Judith M. ; Tung, Chee ; Low, Scott L.

PDF Url : ADA294466

Report Date : 1995

Pagination or Media Count : 18

Abstract : The use of a blade vortex interaction noise prediction scheme, based on CAMRAD/JA, FPR and RAPP, quantifies the effects of errors and assumptions in the modeling of the helicopter's shed vortex on the acoustic predictions. CAMRAD/JA computes the wake geometry and inflow angles that are used in FPR to solve for the aerodynamic surface pressures. RAPP uses these surface pressures to predict the acoustic pressure. Both CAMRAD/JA and FPR utilize the Biot-Savart Law to determine the influence of the vortical velocities on the blade loading and both codes use an algebraic vortex model for the solid body rotation of the vortex core. Large changes in the specification of the vortex core size do not change the inplane wake geometry calculated by CAMRAD/JA and only slighty affect the out-of-plane wake geometry. However, the aerodynamic surface pressure calculated by FPR changes in both magnitude and character with small changes to the core size used by the FPR calculations. This in turn affects the acoustic predictions. Shifting the CAMRAD/JA wake geometry away from the rotor plane by 1/4 chord produces drastic changes in the acoustic predictions indicating that the prediction of acoustic pressure is extremely sensitive to the miss distance between the vortex and the blade and that this distance must be calulated as accurately as possible for acceptable noise predictions. The inclusion or exclusion of a vortex in the FPR-RAPP calculation allows for the determination of the relative importance of that vortex as a BVI noise source. (AN)

Descriptors :   *MATHEMATICAL MODELS, *VORTICES, *WAKE, *NOISE REDUCTION, VELOCITY, PREDICTIONS, COMPUTATIONAL FLUID DYNAMICS, ROTOR BLADES(ROTARY WINGS), VORTEX SHEDDING, HELICOPTERS, AERODYNAMIC LOADING, WIND TUNNEL TESTS, HYDRODYNAMIC CODES, FLOW NOISE, SOUND PRESSURE, WING BODY CONFIGURATIONS, PRESSURE DISTRIBUTION, GAS SURFACE INTERACTIONS, ACOUSTIC FIELDS, MISS DISTANCE, BLADE TIPS.

Subject Categories : Aerodynamics
      Fluid Mechanics
      Helicopters
      Acoustics

Distribution Statement : APPROVED FOR PUBLIC RELEASE