Note
College of Engineering and Computer Science
Member of
Contributors
Publisher
Florida Atlantic University
Date Issued
1991
Description
The atmospheric turbulence that a blade station experiences is called blade-fixed
turbulence. It can qualitatively differ from the conventional body-fixed turbulence
such as experienced by an element of the body or fuselage. This difference is due
to the rotational ,-elocity, which causes fore-and-aft motions of the blade station
through the turbulence waves. A closed-form solution of a frequency-time spectrum
for the dominant vertical turbulence velocity at an arbitrary blade station is
dc,·eloped. This solution makes it possible to explain qualitatively the turbulence
cllcrgy transfer due to rotational velocity from the low-frequency region (< 1P or
1/ rcv.) to the high-frequency(> 1P) region with the occurrence of spectral peaks
and split peaks at 1P /2, 1P, 3P /2, 2P etc. Comparison of blade responses to bladeand
body-fixed turbulence is also presented over a comprehensive range of turbulcuce
scale length and advance ratio; the comparison covers frequency-time spectra,
correlations including standard deviations, and average threshold-crossing rates of
a flapping blade. A major contribution is to formulate both the cyclostationary
turbulence and blade response by the frequency-time spectra, which predict simultaneously
the time- ancl frequency-dependent characteristics such as the energy
culltained in the frequency and time intervals. For low-altitude and low-advanceratio
flights, such as nap-of-the earth or NOE flights, rotational velocity effects on
turbulence modeling qualitatively affect the prediction of turbulence ancl response
statistics.
turbulence. It can qualitatively differ from the conventional body-fixed turbulence
such as experienced by an element of the body or fuselage. This difference is due
to the rotational ,-elocity, which causes fore-and-aft motions of the blade station
through the turbulence waves. A closed-form solution of a frequency-time spectrum
for the dominant vertical turbulence velocity at an arbitrary blade station is
dc,·eloped. This solution makes it possible to explain qualitatively the turbulence
cllcrgy transfer due to rotational velocity from the low-frequency region (< 1P or
1/ rcv.) to the high-frequency(> 1P) region with the occurrence of spectral peaks
and split peaks at 1P /2, 1P, 3P /2, 2P etc. Comparison of blade responses to bladeand
body-fixed turbulence is also presented over a comprehensive range of turbulcuce
scale length and advance ratio; the comparison covers frequency-time spectra,
correlations including standard deviations, and average threshold-crossing rates of
a flapping blade. A major contribution is to formulate both the cyclostationary
turbulence and blade response by the frequency-time spectra, which predict simultaneously
the time- ancl frequency-dependent characteristics such as the energy
culltained in the frequency and time intervals. For low-altitude and low-advanceratio
flights, such as nap-of-the earth or NOE flights, rotational velocity effects on
turbulence modeling qualitatively affect the prediction of turbulence ancl response
statistics.
Language
Type
Form
Extent
144 p.
Subject (Topical)
Identifier
14683
Additional Information
College of Engineering and Computer Science
FAU Electronic Theses and Dissertations Collection
Thesis (M.S.E.)--Florida Atlantic University, 1991.
Date Backup
1991
Date Text
1991
Date Issued (EDTF)
1991
Extension
FAU
FAU
admin_unit="FAU01", ingest_id="ing1508", creator="staff:fcllz", creation_date="2007-07-19 03:00:00", modified_by="staff:fcllz", modification_date="2011-08-16 07:56:33"
IID
FADT14683
Issuance
monographic
Organizations
Attributed name: Florida Atlantic University
Attributed name: College of Engineering and Computer Science
Attributed name: Department of Ocean and Mechanical Engineering
Person Preferred Name
Vellathottam, George V.
Graduate College
Physical Description
144 p.
application/pdf
Title Plain
Frequency-time spectral analysis of helicopter turbulence and response in forward flight
Use and Reproduction
Copyright © is held by the author, with permission granted to Florida Atlantic University to digitize, archive and distribute this item for non-profit research and educational purposes. Any reuse of this item in excess of fair use or other copyright exemptions requires permission of the copyright holder.
http://rightsstatements.org/vocab/InC/1.0/
Origin Information
1991
monographic
Boca Raton, Fla.
Florida Atlantic University
Physical Location
Florida Atlantic University Libraries
Place
Boca Raton, Fla.
Sub Location
Digital Library
Title
Frequency-time spectral analysis of helicopter turbulence and response in forward flight
Other Title Info
Frequency-time spectral analysis of helicopter turbulence and response in forward flight