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Experimental lnvestigation of Separated Shear Flow under Subharmonic Perturbations over a Backward-Facing Step

Ma, Xingyu and Geisler, Reinhard and Schröder, Andreas (2017) Experimental lnvestigation of Separated Shear Flow under Subharmonic Perturbations over a Backward-Facing Step. Flow Turbulence and Combustion, 99, pp. 71-91. Springer. DOI: 10.1007/s10494-017-9814-1 ISSN 1386-6184

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Subharmonic-perturbed shear flow downstream of a two-dimensional backwardfacing step was experimentally investigated. The Reynolds number was Reh = 2.0x104, based on free-stream velocity and step height. Planar 2D-2C particle image velocimetry was employed to measure the separating and reattaching flow in the horizontal-vertical plane in the center position. The subharmonic perturbations were generated by an oscillating flap which was implemented over the step edge and driven by periodic Ampere force. The subharmonic frequency was 55 Hz as the half of the fundamental frequency of the turbulent shear layer. As a result of the subharmonic perturbations, the size of recirculation region behind the backward-facing step is reduced and the time-averaged reattachment length is 31.0% shorter than that of the natural flow. The evolution of vortices, including vortex rollup, growth and breakdown process, is analyzed by using phase-averaging, cross-correlation function and proper orthogonal decomposition. lt is found that Reynolds shear stress is considerably increased in which the vortices roll up and then break down further downstream. In particular, rapid growth of vortices based on the "step mode" occurs at approximate half of the recirculation region, caused by in interaction between the shear layer and the recirculation region. Furthermore, the coherent structures, which are represented by a phasecorrelated POD mode pair, are reconstructed in phases in order to show regular patterns of the subharmonic-perturbed coherent structures.

Item URL in elib:https://elib.dlr.de/118452/
Document Type:Article
Additional Information:ISSN: 1573-1987 (Online); pp 71-91, Volume 99, lssue1, July 2017; Published online: 24 April 2017; ©Springer Science+Business Media Dordrecht 2017
Title:Experimental lnvestigation of Separated Shear Flow under Subharmonic Perturbations over a Backward-Facing Step
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Ma, XingyuXingyu.Ma (at) dlr.deUNSPECIFIED
Geisler, ReinhardReinhard.Geisler (at) dlr.deUNSPECIFIED
Schröder, Andreasandreas.schroeder (at) dlr.dehttps://orcid.org/0000-0002-6971-9262
Journal or Publication Title:Flow Turbulence and Combustion
Refereed publication:Yes
Open Access:No
Gold Open Access:No
In ISI Web of Science:Yes
DOI :10.1007/s10494-017-9814-1
Page Range:pp. 71-91
Keywords:Backward-facing step · Separated shear flow · Subharmonie· Coherentstructure · Particle image velocimetry · Proper orthogonal decomposition
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Aeronautics
HGF - Program Themes:fixed-wing aircraft
DLR - Research area:Aeronautics
DLR - Program:L AR - Aircraft Research
DLR - Research theme (Project):L - Simulation and Validation
Location: Göttingen
Institutes and Institutions:Institute for Aerodynamics and Flow Technology > Experimental Methods, GO
Deposited By: Bachmann, Barbara
Deposited On:25 Jan 2018 15:24
Last Modified:05 Nov 2020 13:35

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