Three-dimensional wake dynamics of a blunt and divergent trailing edge airfoil

El-Gammal, M.; Hangan, Horia

doi:10.1007/s00348-007-0428-6

Cited by 15 publications

(4 citation statements)

References 33 publications

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“…7d) correspond to lower streamwise velocities. As shown by Mansy et al (1994) and Wu et al (1996) in the case of a circular cylinder, and El-Gammal and Hangan (2008) in the case of a blunt trailing edge airfoil, a correlation exists between the small-scale secondary instabilities and spanwise variations of streamwise velocity (u) in the near-wake region, in which both have a similar spanwise wavelength. Considering this correlation, the streamwise velocity (u) data acquired from the PIV measurements have been used here to determine the wavelength of the secondary instabilities.…”

Section: Secondary Instabilitiesmentioning

confidence: 79%

Secondary wake instabilities of a blunt trailing edge profiled body as a basis for flow control

2012

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Flow in the wake of a blunt trailing edge profiled body, comprised of an elliptical leading edge and a rectangular trailing edge, has been investigated experimentally, to identify and characterize the secondary instabilities accompanying the von Kármán vortices. The experiments, which involve laser-induced fluorescence for visualization and particle image velocimetry for quantitative measurement of the wake instabilities, cover Reynolds numbers ranging from 250 to 2,150 based on thickness of the body, to include the wake transition regime. The dominant secondary instability appears as spanwise undulations in von Kármán vortices, which evolve into pairs of counterrotating vortices, with features resembling the instability mechanism predicted by Ryan et al. (J Fluid Mech 538:1-29, 2005). Feasibility of a flow control approach based on interaction with the secondary instability using a series of discrete trailing edge injectors has also been investigated. The control approach mitigates the adverse effects of vortex shedding in certain conditions, where it is able to amplify the secondary instability effectively.

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Section: Secondary Instabilitiesmentioning

confidence: 79%

Secondary wake instabilities of a blunt trailing edge profiled body as a basis for flow control

2012

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“…Later, however, it was shown that the implemented analysis was inadequate and it was suggested that a more complete proper orthogonal decomposition analysis would lead to lower spanwise wavelength values, similar to the ones reported here. In an experimental study of an airfoil with relatively thin finite trailing edge (h TE ¼ 1:8% chord), 26 it was found that the spanwise distribution of ribs does not change with incidence. However, that investigation was performed at significantly lower Reynolds numbers (Re ¼ 0:7 Â 10 6 ; Re TE ¼ 1:26 Â 10 4 ) and the examined incidence range did not exceed a ¼ 6 .…”

Section: Wake Structurementioning

confidence: 99%

“…In fact, while the wake structure downstream of cylinders has received significant attention, this is not the case for the wake of streamlined bodies 25 and even less so for FB airfoils at high Reynolds numbers. 26 However, secondary instabilities in the wake of bluff bodies can be used to implement efficient flow control strategies [27][28][29][30] and their knowledge is crucial. These are knowledge gaps that need to be covered, since FB profiles are now commonly used in wind turbine design.…”

Section: Introductionmentioning

confidence: 99%

Investigation of the three-dimensional flow past a flatback wind turbine airfoil at high angles of attack

Μανωλέσος

Papadakis

2021

Physics of Fluids

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Flatback airfoils are airfoils with a blunt trailing edge. They are currently commonly used in the inboard part of large wind turbine blades, as they offer a number of aerodynamic, structural, and aeroelastic benefits. However, the flow past them at high angles of attack (AoA) has received relatively little attention until now. This is important because they usually operate at high AoA at the inboard part of Wind Turbine blades. The present investigation uses Reynolds averaged Navier-Stokes (RANS) and hybrid RANS þ large eddy simulation predictions to analyze the flow in question. The numerical results are validated against previously published wind tunnel experiments. The analysis reveals that to successfully simulate this flow, the spanwise extent of the computational domain is crucial, more so than the selection of the modeling approach. Additionally, a low-drag regime observed at angles of attack before stall is identified and analyzed in detail. Finally, the complex interaction between the three-dimensional separated flow beyond maximum lift (stall cells) with the vortex shedding from the blunt trailing edge is revealed.

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“…Due to shedding vortices from the blunt trailing edge, the aerodynamic performance of blunt airfoils is unsteady. The shedding vortices adversely increase the base drag and lead to unfavorable noise and aeroelastic problems [26] . In 2011, the authors primarily studied the unsteady characteristics of blunt airfoils and described the unsteady characteristics of lift and drag coefficients of blunt airfoils [27] .…”

Section: Introductionmentioning

confidence: 99%

LES simulation and experimental validation of the unsteady aerodynamics of blunt wind turbine airfoils

Wang

Zhang

Shen

2018

Energy

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In order to investigate the unsteady performance of blunt wind turbine airfoils caused by boundary layer separation and wake eddies, this paper studies the aerodynamic performance by large eddy simulation (LES) and wind tunnel experiment at a Reynolds number of 2.62×10^5. The blunt airfoils are obtained by enlarging the trailing edge of the DU 91-W2-250 airfoil to 6% and 10% chords symmetrically on both pressure and suction sides of the airfoil. The simulation was carried out with the incompressible finite-volume Navier-Stokes code EllipSys3D; and, the experiment was done in a wind tunnel with a cross-section of 0.5m × 0.5m by measuring the surface pressure and wake velocities using ESP-64HD pressure scanner and TSI hot-wire anemometer. The unsteady wake was captured by hot-wire in the wind tunnel, and LES with EllipSys3D. Both experiment and LES show that the spectrum of aerodynamic forces has a broadband nature which is in coincidence with the wake eddies, implying that the unsteady Kármán vortex sheet is the driving mechanism of the force fluctuation. Moreover, the trailing edge size affects the separation bubbles and transition process in the boundary layer. It shows that the boundary layer near the leading edge is unstable in the spanwise direction, which is characterized by low frequency waves.

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Three-dimensional wake dynamics of a blunt and divergent trailing edge airfoil

Cited by 15 publications

References 33 publications

Secondary wake instabilities of a blunt trailing edge profiled body as a basis for flow control

Secondary wake instabilities of a blunt trailing edge profiled body as a basis for flow control

Investigation of the three-dimensional flow past a flatback wind turbine airfoil at high angles of attack

LES simulation and experimental validation of the unsteady aerodynamics of blunt wind turbine airfoils

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