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

Ma, Xingyu; Geisler, Reinhard; Schröder, Andreas

doi:10.1007/s10494-017-9814-1

Cited by 18 publications

(7 citation statements)

References 37 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…According to the previous literatures, Xr behind step was about (4.2~8.6) h when flow was fully turbulent, and it was even longer for a lower Reynold number [1,11,20,30]. To study the evolution process of the CVS, a global view of velocity fields with no less than 10 h (about 60 cm) behind the The flow tunnel was made of transparent PMMA (polymethyl-methacrylate) to provide a clear view for the PIV system.…”

Section: Measurement Systemmentioning

confidence: 99%

“…Hudy et al (2007) [15] further propose a "wake model" that the CVS grow in place before reaching a height equivalent to h, and at this position the CVS shed and accelerate downstream to the ultimate convection speed. This opinion compares the evolution of this flow Various quantitative measurements are applied to obtain velocity or pressure information such as hot-wire, x-wires, hydrogen bubble, laser doppler velocimetry, and particle image velocimetry (PIV) [11,16,20,[26][27][28][29][30]. Many of the measurements can only measure and analyze point-by-point characteristics or time-averaged flow fields information such as X r , turbulent shear stress, turbulent intensity, backflow, and characteristic frequency, etc.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Experimental Investigation of Coherent Vortex Structures in a Backward-Facing Step Flow

Wang

Gao

et al. 2019

Water

View full text Add to dashboard Cite

Coherent vortex structures (CVS) are discovered for more than half a century, and they are believed to play a significant role in turbulence especially for separated flows. An experimental study is conducted for a pressured backward-facing step flow with Reynolds number (Re h ) being 4400 and 9000. A synchronized particle image velocimetry (PIV) system is developed for measurement of a wider range of velocity fields with high resolution. The CVS are proved to exist in the separation-reattachment process. For their temporal evolution, a life cycle is proposed that vortices form in the free shear layer, develop with pairings and divisions and finally shed at the reattachment zone, and sometimes new vortical structures are restructured with recovery of flow pattern. The CVS favor the free shear layer with frequent pairings and divisions particularly at the developing stage around x/h = 2~5 (x: distance from the step in flow direction, h: step height), which may contribute to the high turbulent intensity and shear stress there. A critical distance is believed to exist among CVS, which affects their amalgamation (pairing) and division events. Statistics show that the CVS are well organized in spatial distribution and show specific local features with the flow structures distinguished. The streamwise and vertical diameters (D x and D y ) and width to height ratio (D x /D y ) all obey to the lognormal distribution. With increase of Re h from 4400 to 9000, D x decreases and D y increases, but the mean diameter (D=0.5 × (D x + D y )) keeps around (0.28~0.29) h. As the increase of Re h , the vortical shape change toward a uniform condition, which may be contributed by enhancement of the shear intensity.

show abstract

Section: Measurement Systemmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Experimental Investigation of Coherent Vortex Structures in a Backward-Facing Step Flow

Wang

Gao

et al. 2019

Water

View full text Add to dashboard Cite

show abstract

“…The experiment was carried out in the low-speed wind tunnel at the German Aerospace Center (DLR) and the experimental dataset was obtained by planar PIV. The model, the PIV system and the flow control results have been presented in detailed on a topic of subharmonic-waves by Ma et al 30 Furthermore, the dataset were used for improving accuracy of Reynolds stress calculation by Ma et al 31 For clarity and completeness, the bio-inspired flapping actuator and the basic flow properties are briefly described in the present article.…”

Section: Experimental Datasetmentioning

confidence: 99%

“…Two-dimensional two-component (2D-2C) velocity vector field is obtained by planar PIV in a rectangular field of view covering 240 Â 60 mm 2 in the vertical plane. 30 The vector spacing in the horizontal and vertical directions is 0.3 mm, resulting from a final interrogation window size of 16 Â 16 pixel at 75% overlap. The sampling frequency is 1.7 Hz, which leads to a sequence of 4000 statistically independent velocity vector fields in each flow case.…”

Section: Planar Piv Measurementmentioning

confidence: 99%

“…The free stream flow velocity is U 0 = 10.0 m/s with a turbulence level below 0.15% in the open test section of the wind tunnel. 30 A zero-pressure gradient boundary layer develops over a 900 mm long horizontal flat-plate with an elliptical leading edge and it is artificially tripped near the leading edge for transition to turbulence. The turbulent boundary layer has a thickness of 15.0 mm and a momentum thickness of 2.0 mm on the step edge.…”

Section: Experimental Datasetmentioning

confidence: 99%

See 1 more Smart Citation

Reduced-order coherent structures in active flow separation control using a bio-inspired flapping actuator

Schröder

2018

Proceedings of the Institution of Mechanical Engineers, Part C:

Self Cite

View full text Add to dashboard Cite

An experimental study was conducted to investigate large-scale coherent structures induced by a bio-inspired flapping actuator in a turbulent backward-facing step flow. The flow field velocity dataset in the horizontal-vertical plane was obtained by planar particle image velocimetry. The flapping actuator was implemented over the step edge and it was driven to vertically oscillate, generating periodic small perturbations into the separated shear layer. As a result of active flow control, time-averaged reattachment length was reduced by 31% and Reynolds stresses as well as in-plane turbulent kinetic energy in the separated shear layer were considerably increased. In proper orthogonal decomposition analysis, the first two modes are found to be phase-correlated in the phase portrait of the coefficients. Therefore, reduced-order coherent structures are reconstructed by the first two modes, showing the phase evolution of the vortex shedding process. The extracted reduced-order coherent structures provide a better understanding of the underlying flow physics and are beneficial to effective flow separation control.

show abstract

Unsteady Behavior of a Backward-facing Step in Forced Flow

Chovet

Lippert

Keirsbulck

et al. 2018

Flow Turbulence Combust

View full text Add to dashboard Cite

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L'archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

show abstract

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

Cited by 18 publications

References 37 publications

Experimental Investigation of Coherent Vortex Structures in a Backward-Facing Step Flow

Experimental Investigation of Coherent Vortex Structures in a Backward-Facing Step Flow

Reduced-order coherent structures in active flow separation control using a bio-inspired flapping actuator

Unsteady Behavior of a Backward-facing Step in Forced Flow

Contact Info

Product

Resources

About