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A full-scale rotor-wake investigation of a free-flying helicopter in ground effect using BOS and PIV

Schwarz, Clemens and Bauknecht, Andre and Wolf, Christian and Coyle, Alexander and Raffel, Markus (2020) A full-scale rotor-wake investigation of a free-flying helicopter in ground effect using BOS and PIV. Journal of the American Helicopter Society, 65 (3), pp. 1-20. American Helicopter Society. doi: 10.4050/JAHS.65.032007. ISSN 0002-8711.

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Official URL: https://doi.org/10.4050/JAHS.65.032007

Abstract

Measurements in the wake of a free-flying full-scale helicopter in ground effect were performed for both quasi-steady an unsteady maneuvering flights using stereoscopic particle image velocimetry (PIV), a time-resolved background-oriented schlieren (BOS) setup, and an opt cal marker tracking technique. The systems were used in a complementary way to both visualize blade tip vortices in a large portion of the rotor wake and to capture spatially resolved wake velocity data close to the ground. The high sensitivity of the BOS system enabled the detection of vortices up to an age of ψ = 630◦. Different instability mechanisms as long-wave, short-wave, and pairing instabilities were observed with varying intensity for different flight conditions. A quantitative analysis of vortex locations showed a periodic variation resulting from interactions between consecutive vortices that led to vortex pairing. Characteristics of the wake outwash close to the ground were investigated by means of averaged velocity fields. Different patterns such as wall jet, recirculation, and ground vortex flow were quantitatively analyzed and found to be in good agreement with previous model helicopter experiments. The instantaneous velocity data were used to detect individual blade tip vortices with ages above 450◦ close to the ground and to extract vortex parameters. For a takeoff maneuver, both concentrated vortices and the formation of larger vortex structures due to bundling of several vortices were observed.

Item URL in elib:https://elib.dlr.de/135807/
Document Type:Article
Title:A full-scale rotor-wake investigation of a free-flying helicopter in ground effect using BOS and PIV
Authors:
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Schwarz, ClemensClemens.Schwarz (at) dlr.deUNSPECIFIED
Bauknecht, AndreAndre.Bauknecht (at) dlr.dehttps://orcid.org/0000-0002-4076-780X
Wolf, ChristianChristian.Wolf (at) dlr.dehttps://orcid.org/0000-0002-9052-7548
Coyle, AlexanderUNSPECIFIEDUNSPECIFIED
Raffel, MarkusMarkus.Raffel (at) dlr.dehttps://orcid.org/0000-0002-3340-9115
Date:1 July 2020
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:65
DOI :10.4050/JAHS.65.032007
Page Range:pp. 1-20
Editors:
EditorsEmailEditor's ORCID iD
UNSPECIFIEDVertical Flight SocietyUNSPECIFIED
Publisher:American Helicopter Society
ISSN:0002-8711
Status:Published
Keywords:Full-Scale Helicopter, Particle-Image-Velocimetry (PIV), Background-Oriented Schlieren (BOS), Ground Effect, Free Flight Experiments, Blade-Tip Vortex
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 Virtual Aerodynamic Rotorcraft (old)
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Helicopter, GO
Deposited By: Carter, Beatrice
Deposited On:07 Sep 2020 15:40
Last Modified:07 Sep 2020 15:40

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