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A new methodology for free wake analysis using curved vortex elementsA method using curved vortex elements was developed for helicopter rotor free wake calculations. The Basic Curve Vortex Element (BCVE) is derived from the approximate Biot-Savart integration for a parabolic arc filament. When used in conjunction with a scheme to fit the elements along a vortex filament contour, this method has a significant advantage in overall accuracy and efficiency when compared to the traditional straight-line element approach. A theoretical and numerical analysis shows that free wake flows involving close interactions between filaments should utilize curved vortex elements in order to guarantee a consistent level of accuracy. The curved element method was implemented into a forward flight free wake analysis, featuring an adaptive far wake model that utilizes free wake information to extend the vortex filaments beyond the free wake regions. The curved vortex element free wake, coupled with this far wake model, exhibited rapid convergence, even in regions where the free wake and far wake turns are interlaced. Sample calculations are presented for tip vortex motion at various advance ratios for single and multiple blade rotors. Cross-flow plots reveal that the overall downstream wake flow resembles a trailing vortex pair. A preliminary assessment shows that the rotor downwash field is insensitive to element size, even for relatively large curved elements.
Document ID
19910009754
Acquisition Source
Legacy CDMS
Document Type
Contractor Report (CR)
Authors
Bliss, Donald B. (Continuum Dynamics, Inc. Princeton, NJ, United States)
Teske, Milton E. (Continuum Dynamics, Inc. Princeton, NJ, United States)
Quackenbush, Todd R. (Continuum Dynamics, Inc. Princeton, NJ, United States)
Date Acquired
September 6, 2013
Publication Date
December 1, 1987
Subject Category
Aerodynamics
Report/Patent Number
NASA-CR-3958
CDI-84-6
NAS 1.26:3958
Accession Number
91N19067
Funding Number(s)
PROJECT: RTOP 505-61-51
CONTRACT_GRANT: NAS2-11295
Distribution Limits
Public
Copyright
Work of the US Gov. Public Use Permitted.

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