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Wake Unsteadiness and Tip Vortex System of Full–Scale Helicopters in Ground Effect

Wolf, Christian and Weiss, Armin and Schwarz, Clemens and Braukmann, Johannes N. and Koch, Stefan and Raffel, Markus (2021) Wake Unsteadiness and Tip Vortex System of Full–Scale Helicopters in Ground Effect. In: Vertical Flight Society's 77th Annual Forum and Technology Display. Vertical Flight Society's 77th Annual Forum 2021, 10.-14. Mai 2021, Virtuell.

Full text not available from this repository.

Official URL: https://vtol.org/annual-forum/forum-77-proceedings-and-access

Abstract

The main rotor wake of free–flying helicopters in ground effect was investigated during a measurement campaign with the DLR test rotorcraft Airbus Bo105 and EC135. An advanced measurement system combined high–speed schlieren imaging with point–wise constant temperature anemometry for a comprehensive analysis of the flow. In hover conditions, the wake structure was similar to earlier data, in spite of the environmental conditions, which were found to have a significant influence. The schlieren system tracked the blade tip vortices convecting along the slipstream boundary. Depending on the rotorcraft, the vortices developed either instabilities of individual filaments or cooperative pairing instabilities. Both instability types occurred one to two revolutions below the rotor plane, and the decayed tip vortices fell below the schlieren sensitivity limit soon after. The velocity footprint of the vortices was detected by fiber–film sensors further downstream along the slipstream boundary, but harmonic oscillations play a minor role in comparison to broad–banded turbulence with a Kolmogorov–like spectrum. The wake was found to be hover–like for vertical take–off cases until breaking down into low–frequency oscillations when exceeding a hub height of approximately 1.4 rotor radii. In forward flight conditions, blade–vortex interactions were found in the frontal area of the main rotor plane, and between the main rotor tip vortices and the Bo105’s tail rotor.

Item URL in elib:https://elib.dlr.de/141956/
Document Type:Conference or Workshop Item (Speech)
Title:Wake Unsteadiness and Tip Vortex System of Full–Scale Helicopters in Ground Effect
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Wolf, ChristianChristian.Wolf (at) dlr.dehttps://orcid.org/0000-0002-9052-7548
Weiss, ArminArmin.Weiss (at) dlr.dehttps://orcid.org/0000-0002-7532-2974
Schwarz, ClemensClemens.Schwarz (at) dlr.deUNSPECIFIED
Braukmann, Johannes N.Johannes.Braukmann (at) dlr.dehttps://orcid.org/0000-0001-8046-9623
Koch, StefanStefan.Koch (at) dlr.deUNSPECIFIED
Raffel, MarkusMarkus.Raffel (at) dlr.dehttps://orcid.org/0000-0002-3340-9115
Date:May 2021
Journal or Publication Title:Vertical Flight Society's 77th Annual Forum and Technology Display
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In SCOPUS:No
In ISI Web of Science:No
Status:Published
Keywords:Helicopter, Rotor Wake, Background Oriented Schlieren, Constant Temperature Anemometry, Full-Scale Testing, Blade Tip Vortex
Event Title:Vertical Flight Society's 77th Annual Forum 2021
Event Location:Virtuell
Event Type:international Conference
Event Dates:10.-14. Mai 2021
Organizer:Vertical Flight Society
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:Efficient Vehicle
DLR - Research area:Aeronautics
DLR - Program:L EV - Efficient Vehicle
DLR - Research theme (Project):L - Virtual Rotorcraft and Validation
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Helicopter, GO
Institute for Aerodynamics and Flow Technology > High Speed Configurations, GO
Deposited By: Carter, Beatrice
Deposited On:14 Jul 2021 14:51
Last Modified:14 Jul 2021 15:36

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