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Experimental investigation of Fenestron noise

Olsman, W.F.J. (2022) Experimental investigation of Fenestron noise. Journal of the American Helicopter Society, 67 (3), pp. 16-27. American Helicopter Society. doi: 10.4050/JAHS.67.032002. ISSN 0002-8711.

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Official URL: https://doi.org/10.4050/JAHS.67.032002

Abstract

The noise radiation of an EC135 Fenestron is investigated by means of flight tests. The noise emission was measured with ground microphones during several different maneuvers. These include hover, rearward flight, and forward flight at different combinations of the side slip angle and the airspeed. In hover, a high level of broadband noise is observed. A comparison with available engine noise data suggested that engine noise is not dominant in hover. In rearward flight, the Fenestron may encounter a relatively clean aerodynamic inflow. However, the measurements do not indicate a reduction in noise radiation of the Fenestron. For rearward flight, a significant increase in main rotor noise is observed. Flights at different combinations of the side slip angle and airspeed show that the Fenestron radiates high levels of tonal noise at high-speed flight at negative side slip. The most likely cause for this is a highly disturbed inflow caused by flow separations of the diffusor outlet edge and the sharp trailing edges of the stator blades. Measurements of the tail boom yaw moment and Fenestron drive shaft torque imply that a reverse flow is possible at medium airspeed, while the Fenestron thrust does not reverse sign. Only at higher airspeeds and negative side slip, it is possible to achieve a thrust reversal in addition to a flow reversal.

Item URL in elib:https://elib.dlr.de/138687/
Document Type:Article
Title:Experimental investigation of Fenestron noise
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Olsman, W.F.J.jurrien.olsman (at) dlr.deUNSPECIFIED
Date:July 2022
Journal or Publication Title:Journal of the American Helicopter Society
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:67
DOI:10.4050/JAHS.67.032002
Page Range:pp. 16-27
Editors:
EditorsEmailEditor's ORCID iD
UNSPECIFIEDigenta connectUNSPECIFIED
Publisher:American Helicopter Society
ISSN:0002-8711
Status:Published
Keywords:acoustics, helicopter, Fenestron, tail rotor noise
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:rotorcraft
DLR - Research area:Aeronautics
DLR - Program:L RR - Rotorcraft Research
DLR - Research theme (Project):L - The Quiet und Comfortable Rotorcraft (old)
Location: Braunschweig
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Helicopter, BS
Deposited By: Olsman, WFJ
Deposited On:11 Oct 2022 12:02
Last Modified:11 Oct 2022 12:02

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