Wake instabilities of a blunt trailing edge profiled body at intermediate Reynolds numbers

Naghib-Lahouti, Arash; Lavoie, Philippe; Hangan, Horia

doi:10.1007/s00348-014-1779-4

Cited by 19 publications

(37 citation statements)

References 26 publications

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“…Thus far, all results presented regarding the secondary wake vortices suggest that the cylinder mode B is the dominant secondary instability within the wake of the elongated blunt body studied here with AR = 46.5 for Re(h) = 3500, 5200, and 7000. No evidence of the BTE mode B nor S has been found within the collected data as was anticipated from the stability analysis of Ryan et al (2005) for 2.5 AR 17.5 and a maximum Re(h) of 700 and the experimental work of Naghib-Lahouti et al (2012, 2014 for AR = 12.5 and 250 Re(h) 5 × 10 4 , although we would like to emphasise the large differences in AR between these studies and the present investigation. The visual inspection and spatialcorrelation analysis of both the time-resolved and statistical stereo-PIV data have been used to reach this conclusion.…”

Section: Temporal Behaviour Of the Streamwise Wake Vorticescontrasting

confidence: 39%

“…(i) Provide experimental insight regarding the wake modes of a highly elongated blunt body. The analysis will extend the numerical predictions made by Ryan et al (2005) for 2.5 AR 17.5 and also the experimental investigations of Naghib-Lahouti et al (2012, 2014 at AR = 12.5 to a larger AR of 46.5, which is more relevant to industrial applications. Specifically, the secondary instability in the wake will be statistically characterised in terms of spanwise wavelength and the spatio-temporal symmetry of the vortices.…”

Section: Introductionmentioning

confidence: 60%

“…The relationship between the secondary instability and the upstream boundary layer is explored by tracking the spacing and evolution of the low-speed structures in the boundary layer as they move past the BTE and by determining the strength of the streamwise vortices in both the boundary layer and wake. Finally, the proper-orthogonal-decomposition-based analysis used by Naghib-Lahouti et al (2012, 2014 is applied here to compare the present results with previous estimations of the secondary instability wavelength.…”

Section: Introductionmentioning

confidence: 86%

“…Re(h) 5 × 10 4 by Naghib-Lahouti et al (2012, 2014. Both investigations found secondary instability wavelengths varying from 2.0 to 2.5h.…”

Section: Introductionmentioning

confidence: 90%

“…The use of POD on snapshots of the fluctuating component of streamwise velocity (u ) in the x-z plane of the wake is investigated in this section. This is done to study the energy content of the secondary instability in the wake and to carry out characterisation of the secondary instability wavelength (λ z ) using the POD-based method applied by Naghib-Lahouti et al (2012, 2014. This comparison is primarily motivated by the differences in the wake structures reported between these studies and the present investigation, as it is not clear if the differences are physical or an artifact of the analysis techniques used.…”

Section: The Proper Orthogonal Decomposition Of Streamwise Velocity Imentioning

confidence: 99%

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Secondary instabilities in the wake of an elongated two-dimensional body with a blunt trailing edge

2018

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The secondary instability in the wake of a two-dimensional blunt body with a chord to thickness ratio of 46.5 was experimentally investigated for Reynolds numbers of 3500, 5200 and 7000 based on the blunt trailing edge height $h$. Planar, stereoscopic and high-speed particle image velocimetry (PIV) measurements were performed to characterise the wake and upstream boundary layer. The same mode B secondary instability that is found in the cylinder wake was found to be present in the wake of the elongated body studied here. The most probable wavelength of the secondary instability, defined as the spanwise distance between adjacent streamwise vortex pairs in the wake, was found to range from $0.7h$ to $0.8h$ by applying a spatial autocorrelation to the spanwise–wall-normal instantaneous fields of the $Q$-criterion. The temporal evolution of the secondary wake vortices was investigated using time-resolved stereoscopic PIV measurements and it was shown that the vortices maintain both their directions of rotation and spanwise positions during the primary vortex shedding cycles. In agreement with previous literature, the secondary instability did not greatly change as the upstream boundary layer transitioned from laminar to turbulent. Moreover, any upstream boundary layer structures were found to rapidly evolve into wake structures just past the blunt trailing edge. The wavelength of the secondary instability was shown to match the spanwise distance between adjacent low-speed zones of streamwise velocity in the wake. These undulating velocity patterns proved to be a viable method for determining the secondary instability wavelength; however, this type of analysis is highly sensitive to the energy content used for data reconstruction when proper orthogonal decomposition is applied beforehand.

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Section: Temporal Behaviour Of the Streamwise Wake Vorticescontrasting

confidence: 39%