Volumetric Velocity Measurements in the Wake of a Hemispherical Roughness Element

Johnson, Kyle; Thurow, Brian S.; Kim, Tae-Hoon; Blois, Gianluca; Christensen, Kenneth T.

doi:10.2514/1.j055454

Cited by 22 publications

(14 citation statements)

References 25 publications

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“…In the vast body of literature concerning flow around finite width, wall‐mounted obstacles—such as hemispheres (Acarlar & Smith, ; Carr & Plesniak, ; Johnson et al, ; Manhart, ; Wood et al, ), ellipsoids (Hajimirzaie & Buchholz, ), cubes (Martinuzzi & Tropea, ), cylinders (Hajimirzaie et al, ; Kim & Christensen, ; Pattenden et al, ; Sumner, ), and axisymmetric hills (Garcia‐Villalba et al, ; Lardeau et al, )—observations of, and models for, the vortex structure in the wake have been presented that are relevant to the interpretation of the results presented herein. While many of these studies have been undertaken in thin boundary layers or at relatively low

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—allowing the identification of large‐scale vortices in the wake to be somewhat simpler—all of these studies have identified vortices with a significant streamwise component similar to that identified herein.…”

Section: Discussionmentioning

confidence: 99%

Secondary Flows and Vortex Structure Associated With Isolated and Interacting Barchan Dunes

et al. 2020

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The three‐dimensional, crescentic morphology of a barchan dune induces secondary flows and a complex vortex structure in its wake. In scenarios where barchans are in close proximity to each other, the flow modifications introduced by the wake of the upstream barchan are important for understanding the morphodynamics of the downstream barchan. The results herein detail the flow structure in a plane normal to the mean flow (cross‐plane) through stereo particle image velocimetry measurements in a refractive‐index‐matching flow facility, utilizing solid, fixed‐bed barchan models. Spatial distributions of streamwise‐oriented swirling motions and Reynolds shear stress components reveal distinct flow regimes in the wake region of an isolated barchan: flow downstream of the horn tips and flow in the separated shear layer closer to the centerline. Streamwise rollers appear downstream of the horns, and measurements upstream demonstrate their origin on the stoss side of the dune in the form of a horseshoe vortex. Flow downstream of the separated shear layer in the wake embodies features consistent with that of hairpin vortices shed from the arched crestline of the barchan. These structures constitute the induction of secondary flows in the flow that, in the case of barchans in close proximity with a lateral offset, are preferentially amplified in accordance with local topography. Further analysis reveals the spatial scales and turbulent stresses associated with these structures, which are discussed in the context of larger fields of bedforms and the formation of protodunes.

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Section: Discussionmentioning

confidence: 99%

Secondary Flows and Vortex Structure Associated With Isolated and Interacting Barchan Dunes

et al. 2020

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“…Acarlar & Smith 1987;Martinuzzi & Tropea 1993;Manhart 1998;Pattenden, Turnock & Zhang 2005;Wood et al 2016). These flows differ significantly from cases where the obstacle extends only to the log layer of the turbulent boundary layer (up to H/δ ≈ 0.2, where δ is the boundary layer thickness), at which point it is more appropriately viewed as a roughness element, exposed to much higher turbulence levels (Tomkins 2001;Ryan, Ortiz-Dueñas & Longmire 2011;Zheng & Longmire 2014;Pathikonda & Christensen 2015;Johnson et al 2017;Tan & Longmire 2017;Tang et al 2016;Kim & Christensen 2018).…”

Section: Introductionmentioning

confidence: 99%

Unsteady dynamics of turbulent flow in the wakes of barchan dunes modulated by overlying boundary-layer structure

et al. 2021

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“…The result is a compact camera capable of sampling volumetric information in instantaneous snapshots, thereby enabling many possibilities in the realm of flow diagnostics. The Advanced Flow Diagnostics Laboratory (AFDL) of Auburn University has constructed many plenoptic cameras for use in PIV [16][17][18][19][20] and PTV [21][22][23], with a recent focus on scalar-field diagnostics, such as background-oriented schlieren [24], chemiluminescence [25], and pyrometry [25]. Although volumetric reconstructions can be performed using a thin-lens assumption, a volumetric calibration procedure provides many advantages.…”

Section: Plenoptic Camerasmentioning

confidence: 99%

“…Thus, every camera samples both angular and spatial content (i.e., the light field). A few methods exist to capture multiple views per camera: (1) fiber optic bundles that branch from the main sensor with independent optics and mounting, effectively creating miniature cameras, have been used for optical coherence tomography [5,6] and background oriented schlieren (BOS) [7]; (2) relay prisms and mirrors in front of the primary objective produce either a stereoscope [8] or a quadscope [9], which have been demonstrated for a variety of high-speed diagnostic techniques, including tomo-PIV [10,11], LIF [9,12], and multi-color LIF [13,14]; (3) insertion of a microlens array between the primary objective and imaging sensor creates a plenoptic camera [15], which has been used for a wide variety of applications, including PIV [16][17][18][19][20], PTV [21][22][23], background-oriented schlieren [24], chemiluminescence [25], and pyrometry [25].…”

Section: Introductionmentioning

confidence: 99%

On the Impact of Subaperture Sampling for Multispectral Scalar Field Measurements

Clifford¹,

Thurow²

2020

Optics

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The novel 3D imaging and reconstruction capabilities of plenoptic cameras are extended for use with continuous scalar fields relevant to reacting flows. This work leverages the abundance of perspective views in a plenoptic camera with the insertion of multiple filters at the aperture plane. The aperture is divided into seven regions using off-the-shelf components, enabling the simultaneous capture of up to seven different user-selected spectra with minimal detriment to reconstruction quality. Since the accuracy of reconstructed features is known to scale with the available angular information, several filter configurations are proposed to maintain the maximum parallax. Three phantoms inspired by jet plumes are simulated onto an array of plenoptic cameras and reconstructed using ASART+TV with a variety of filter configurations. Some systematic challenges related to the non-uniform distribution of views are observed and discussed. Increasing the number of simultaneously acquired spectra is shown to incur a small detriment to the accuracy of reconstruction, but the overall loss in quality is significantly less than the gain in spectral information.

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Volumetric Velocity Measurements in the Wake of a Hemispherical Roughness Element

Cited by 22 publications

References 25 publications

Secondary Flows and Vortex Structure Associated With Isolated and Interacting Barchan Dunes

Secondary Flows and Vortex Structure Associated With Isolated and Interacting Barchan Dunes

Unsteady dynamics of turbulent flow in the wakes of barchan dunes modulated by overlying boundary-layer structure

On the Impact of Subaperture Sampling for Multispectral Scalar Field Measurements

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