On the volumetric reconstruction of transiting wakes using stereoscopic-PIV

Bond, Clinton; Marzanek, Matthew; Neeteson, Nathan; Rival, David E.

doi:10.1007/s00348-019-2802-6

Cited by 3 publications

(6 citation statements)

References 10 publications

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“…Laser sheet and cameras were fixed, while the model was towed through thus allowing for a scanning reconstruction; see the work of Bond et al. (2019). Figure 2( b , c ) shows a schematic of the sPIV set-up.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…As the laser sheet location was fixed, starting the acceleration earlier or later allowed one to capture a different stage of the dynamic process via the sPIV set-up, as explained by Bond et al. (2019). In figure 3, the instantaneous velocity () is plotted against the dimensionless distance () for and .…”

Section: Experimental Methodsmentioning

confidence: 99%

“…To quantify the development of the cross-flow separation, we used a time-resolved stereoscopic particle image velocimetry (sPIV) system. Laser sheet and cameras were fixed, while the model was towed through thus allowing for a scanning reconstruction; see the work of Bond et al (2019). Figure 2(b,c) shows a schematic of the sPIV set-up.…”

Section: Experimental Set-upmentioning

confidence: 99%

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Dynamic separation on an accelerating prolate spheroid

Guo,

Kaiser,

Rival

2023

J. Fluid Mech.

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Time-varying flow separation on an accelerating prolate spheroid has been studied at various angles of incidence. Instantaneous pressure and scanning stereoscopic particle image velocimetry were used to shed light on the evolution of cross-flow structures for the Reynolds number ( $Re$ ) range of $1.0\times 10^6\leq Re \leq 1.5\times 10^6$ . The movement of separation lines is examined for various model accelerations to investigate on the interplay between acceleration and flow separation. The results demonstrate that for axial accelerations, the streamwise pressure distribution in the rear part of the prolate spheroid switches from an adverse to a favourable pressure gradient. At the same time, the circumferential adverse pressure gradient present during steady motion vanishes during said accelerations. In contrast, both streamwise and circumferential adverse pressure gradients strengthen when the model is axially decelerated. These dynamic pressure distributions influence the location of the separation line, which in turn moves closer to the model meridian during accelerations while moving outwards during decelerations. The streamwise vorticity distribution and the streamwise circulation both show how the separation-line position impacts the vortex formation. A high-vorticity region near the model surface is established during acceleration. In contrast, a decelerating model leads to transport of high-vorticity fluid into the outer area of the cross-flow separation. We further assess the memory effects following the near-impulsive velocity changes. The cross-flow retains the memory of moving separation lines shortly after the acceleration. However, the separation recovers quickly to a steady state.

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Section: Experimental Methodsmentioning

confidence: 99%

Section: Experimental Methodsmentioning

confidence: 99%

Section: Experimental Set-upmentioning

confidence: 99%

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Dynamic separation on an accelerating prolate spheroid

Guo,

Kaiser,

Rival

2023

J. Fluid Mech.

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“…Scanning stereoscopic particle image velocimetry (sPIV) measurements, as described in Bond et al (2019), were conducted to obtain the phase-averaged velocity distribution and provide insight into the generation of the complete vorticity field over the prolate-spheroid body. In a stationary measurement system, it is reasonable to assume that structures remain frozen in the wake based on Taylor's frozen-flux hypothesis (Taylor 1938;Townsend 1980;Zaman and Hussain 1981).…”

Section: Scanning Stereoscopic Particle Image Velocimetrymentioning

confidence: 99%

“…However, to the best of the authors' knowledge, the 3D flowfield around a prolate spheroid (sketch in Figure 1b) has not yet been captured experimentally. In the present study, we use a moving model to apply the scanning stereo-PIV approach presented in Bond et al (2019). The approach allows one to gather volumetric flowfield data of the complex crossflow separation for a wide variety of boundary conditions at high Re and with reasonable experimental effort.…”

Section: Introductionmentioning

confidence: 99%

Vortex-wake formation and evolution on a prolate spheroid at subcritical Reynolds numbers

Guo

Kaiser

Rival

2023

Preprint

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Three-dimensional (3D) flow reconstruction over a 6:1 prolate spheroid using scanning stereoscopic particle image velocimetry has been conducted in a towing-tank facility. Forces, moments, surface pressure and reconstructed 3D vortical-flow structures are acquired in order to characterize the separated flow within the subcritical regime at three Reynolds numbers (Re = 0.5 × 106, 1.0 × 106 and 1.5 × 106), and at four incidence angles (α = 5◦, 10◦, 15◦ and 20◦). Key flow features are evaluated through the reconstructed 3D flowfield data. In particular, the interaction of the crossflow vortices and the surface-pressure distribution are discussed. It is shown that the crossflow vortices consist of helical vortex tubes as the dominant coherent structures, which are more distinct at large α. For α ≥ 15◦, four high-vorticity regions were observed. A pair of upper vortex tubes, originate on the windward side of the model, while a lower vortex tube is formed on the strong curvature region on the leeward side of the model. The vortex dynamics are further characterized through stretching and tilting terms via the vorticity-transport equation. Larger incidence angles α lead to a stronger alignment of the crossflow vortices with the mean flow direction, which is reflected in the tilting terms. A weak Re dependency of the loads and flow structures within the range 1.0 × 106 ≤ Re ≤ 1.5 × 106 is reported, while a significantly different result was captured for separation at Re = 0.5 × 106. An increase in separation size at Re = 0.5 × 106 at 20◦ results in an additional flow structure; a pair of secondary vortices is formed, leading to a change in the pressure distribution on the model surface when compared to higher Re.

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