Bluff body wakes with free, fixed, and discontinuous separation at low Reynolds numbers and low aspect ratio

Petrusma, M. S.; Gai, S. L.

doi:10.1007/bf00190274

Cited by 16 publications

(6 citation statements)

References 18 publications

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“…6). Petrusma and Gai (1996) have observed similar secondary peaks and have attributed them to the effects of the large-scale secondary wake instability …”

Section: The Von Kármán Vortex Streetmentioning

confidence: 56%

“…This process, which starts at Reynolds numbers as low as Re(d) = 49 in the case of circular cylinder (Williamson 1996), continues to remain the primary instability mechanism in the wake, although its intensity and frequency vary as Reynolds number increases. While the trend of variation of vortex shedding frequency with Reynolds numbers is different for different profile geometries, this trend is often found to be affected by discontinuities, which have been attributed to secondary instabilities, as noted by Eisenlohr and Eckelmann (1988), Bull et al (1995), and Petrusma and Gai (1996).…”

Section: Introductionmentioning

confidence: 91%

“…The geometric configuration of the body studied herein (an elliptical leading edge followed by a rectangular section) is similar to the ones studied by Selby and Miandoab (1990), Bearman and Tombazis (1993), Petrusma and Gai (1996), Kim et al (2004), Mills et al (2005), Park et al (2006), Pastoor et al (2008), andStanlov et al (2010). The geometric proportions of the body (shown in Fig.…”

Section: Introductionmentioning

confidence: 95%

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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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“…6). Petrusma and Gai (1996) have observed similar secondary peaks and have attributed them to the effects of the large-scale secondary wake instability …”

Section: The Von Kármán Vortex Streetmentioning

confidence: 56%

Section: Introductionmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 95%

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

2012

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“…At this point, the vorticity concentration in the wake is once again asymmetric and the cycle repeats. This process forms the well-known von Kármán vortex street and has been shown to begin as low as Re(d) = 40 in the case of a circular cylinder with diameter d (Roshko 1954) and Re(h) = 154 in the case of a two-dimensional body with a BTE of height h (Petrusma & Gai 1996). Further increasing Re leads to the onset of threedimensionality in the wake and eventually a transition to turbulence, which occurs by either large-scale distortion of the primary spanwise vortices or by the amplification of Tollmien-Schlichting waves in the separated shear layers (Bloor 1964).…”

Section: Introductionmentioning

confidence: 93%

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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“…One is to use segmented trailing edges. The effect of geometry on the base pressure recovery of segmented blunt trailing edges was investigated by Petrusma and Gai (1994), while a comparison experiment was carried out by Petrusma and Gai (1996) to examine the bluff body wake with free, fixed, and discontinuous separation. Bearman (1965) found that the decrease of base drag with an increase of formation length has been linked to the curvature of the separated shear layer.…”

Section: Introductionmentioning

confidence: 99%

Experimental investigation of the mean and fluctuating forces of wavy (varicose) cylinders in a cross-flow

Lam

Wang

et al. 2004

Journal of Fluids and Structures

106

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Bluff body wakes with free, fixed, and discontinuous separation at low Reynolds numbers and low aspect ratio

Cited by 16 publications

References 18 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

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

Experimental investigation of the mean and fluctuating forces of wavy (varicose) cylinders in a cross-flow

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