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The Onset of Dynamic Stall Revisited

Mulleners, Karen und Raffel, Markus (2012) The Onset of Dynamic Stall Revisited. Experiments in Fluids, 52 (3), Seiten 779-793. DOI: 10.1007/s00348-011-1118-y ISSN 0723-4864

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Offizielle URL: http://www.springerlink.com/content/0723-4864/52/3/


Dynamic stall on a helicopter rotor blade comprises a series of complex aerodynamic phenomena in response to the unsteady change of the blade’s angle of attack. It is accompanied by a lift overshoot and delayed massive flow separation with respect to static stall. The classical hallmark of the dynamic stall phenomenon is the dynamic stall vortex. The flow over an oscillating OA209 airfoil under dynamic stall conditions was investigated by means of unsteady surface pressure measurements and time–resolved particle image velocimetry. The characteristic features of the unsteady flow field were identified and analysed utilising different coherent structure identification methods. An Eulerian and a Lagrangian procedure were adopted to locate the axes of vortices and the edges of Lagrangian coherent structures, respectively; a proper orthogonal decomposition of the velocity field revealed the energetically dominant coherent flow patterns and their temporal evolution. Based on the complementary information obtained by these methods the dynamics and interaction of vortical structures were analysed within a single dynamic stall life cycle leading to a classification of the unsteady flow development into five successive stages: the attached flow stage; the stall development stage; stall onset; the stalled stage; and flow reattachment. The onset of dynamic stall was specified here based on a characteristic mode of the proper orthogonal decomposition of the velocity field. Variations in the flow field topology that accompany the stall onset were verified by the Lagrangian coherent structure analysis. Furthermore, the orientation of the trajectories of vortices that originated at the very leading edge shortly before and after stall onset was observed to be altered. The mechanism that results in the detachment of the dynamic stall vortex from the airfoil was identified as vortex induced separation caused by strong viscous interactions. Finally, a revised criterion to discern between light and deep dynamic stall was formulated.

Zusätzliche Informationen:Published online: 24. May 2011
Titel:The Onset of Dynamic Stall Revisited
AutorenInstitution oder E-Mail-AdresseAutoren-ORCID-iD
Mulleners, Karenkaren.mulleners@dlr.deNICHT SPEZIFIZIERT
Raffel, Markusmarkus.raffel@dlr.deNICHT SPEZIFIZIERT
Erschienen in:Experiments in Fluids
Referierte Publikation:Ja
In Open Access:Nein
In ISI Web of Science:Ja
DOI :10.1007/s00348-011-1118-y
Seitenbereich:Seiten 779-793
Stichwörter:dynamic stall, time–resolved PIV, coherent structure analysis, unsteady separation
HGF - Forschungsbereich:Luftfahrt, Raumfahrt und Verkehr
HGF - Programm:Luftfahrt
HGF - Programmthema:Drehflügler (alt)
DLR - Schwerpunkt:Luftfahrt
DLR - Forschungsgebiet:L RR - Drehflüglerforschung
DLR - Teilgebiet (Projekt, Vorhaben):L - Der virtuelle Drehflügler (alt)
Standort: Göttingen
Institute & Einrichtungen:Institut für Aerodynamik und Strömungstechnik > Hubschrauber
Hinterlegt von: Mulleners, Karen
Hinterlegt am:01 Mär 2012 15:16
Letzte Änderung:07 Dez 2015 02:23

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