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The effects of vortex modeling on blade-vortex interaction noise predictionThe 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 slightly 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 calculated 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.
Document ID
19960001162
Acquisition Source
Legacy CDMS
Document Type
Technical Memorandum (TM)
Authors
Gallman, Judith M. (NASA Ames Research Center Moffett Field, CA, United States)
Tung, Chee (NASA Ames Research Center Moffett Field, CA, United States)
Low, Scott L. (NASA Ames Research Center Moffett Field, CA, United States)
Date Acquired
September 6, 2013
Publication Date
January 1, 1995
Subject Category
Acoustics
Report/Patent Number
AD-A294466
NASA-TM-110823
NAS 1.15:110823
Accession Number
96N11163
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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