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Flap-lag damping in hover and forward flight with a three-dimensional wakePrediction of lag damping is difficult owing to the delicate balance of drag, induced drag and Coriolis forces in the in-plane direction. Moreover, induced drag is sensitive to dynamic wake, both shed and trailing components, and thus its prediction requires adequate unsteady-wake representation. Accordingly, rigid-blade flap-lag equations are coupled with a three-dimensional finite-state wake model; three isolated rotor configurations with three, four and five blades are treated over a range of thrust levels, Lock numbers, lag frequencies and advance ratios. The investigation includes convergence characteristics of damping with respect to the number of radial shape functions and harmonics of the wake model for multiblade modes of low frequency (less than 1/rev.) to high frequency (greater than 1/rev.). Predicted flap and lag damping levels are then compared with similar predictions with (1) rigid wake (no unsteady induced flow, (2) Loewy lift defficiency and (3) dynamic inflow. The coverage also includes correlations with the measured lag regressive-mode damping in hover and forward flight and comparisons with similar correlations with dynamic wake model are consistently higher than the predictions with the dynamic inflow model; even for the low frequency lag regressive mode, the number of wake harmonics should at least be equal to twice the number of blades.
Document ID
19950040968
Acquisition Source
Legacy CDMS
Document Type
Reprint (Version printed in journal)
Authors
Manjunath, A. R.
(Indian Inst. of Science Bangalore, India)
Nagabhushanam, J.
(Indian Inst. of Science Bangalore, India)
Gaonkar, Gopal H.
(Florida Atlantic Univ. Boca Raton, FL, United States)
Peters, David A.
(Washington Univ. Saint Louis, MO, United States)
Su, AY
(Yuan-Ze Inst. of Tech. Chungli, Taiwan)
Date Acquired
August 16, 2013
Publication Date
October 1, 1993
Publication Information
Publication: American Helicopter Society, Journal
Volume: 38
Issue: 4
ISSN: 0002-8711
Subject Category
Aerodynamics
Accession Number
95A72567
Funding Number(s)
CONTRACT_GRANT: DAAL03-91-G-0007
CONTRACT_GRANT: NAG2-462
Distribution Limits
Public
Copyright
Other

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