Flow structure in the wake of a low-aspect-ratio wall-mounted bluff body

Hajimirzaie, Seyed M.

doi:10.17077/etd.l1o4bniu

Cited by 2 publications

(2 citation statements)

References 93 publications

(309 reference statements)

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“…The wake structures, vortex shedding behavior, and primary parameters governing the flow fields around wall-mounted obstacles including obstacle shape, aspect ratio (AR = height/width = H/D), boundary layer characteristics, and Reynolds number have been studied extensively for decades as reviewed in detail by Hajimirzaie (2013). In particular, much attention has been given…”

Section: Introductionmentioning

confidence: 99%

“…In the case of dipole wakes, bending and reconnection of Kármán vortices occurs only at the free end resulting in a "half-loop" structure (Hosseini et al, 2013). Hajimirzaie (2013) reviewed the wake structures and shedding dynamics of wall-mounted bodies of AR ≈ 1 including hemispheres, spheres, tapered plates, pyramids, and cones. In particular, the detailed review of research on the origins of vortices in the near wake demonstrated that the wake structures (tip, base, and spanwise vortices) and their dynamics can be highly varied for obstacles of AR ≈ 1 depending on obstacle shape and flow conditions (i.e., Re and δ/D or δ/H).…”

Section: Introductionmentioning

confidence: 99%

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Flow patterns around confined low-aspect-ratio obstacles

Hajimirzaie

Buchholz

2023

Preprint

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An experimental study was conducted on the wakes around three different obstacles confined between two parallel walls: semi-ellipsoids with the major axes of the base ellipses aligned in the streamwise and transverse directions, and a sphere. The Reynolds number was 1.78 × 104 based on ellipsoid height, H, and sphere diameter, D. The study was performed using thermal anemom-etry and two-dimensional digital particle image velocimetry. Common to each of these geometries is a convex surface of the obstacle intersecting the top and/or bottom walls, which was shown to result in a wall jet in the vicinity of the junction. Large streamwise counter-rotating vortex structures were found to be a robust feature of the wakes, which are referred to as lobes, due to their resemblance to previously coined lobe structures identified in the wake of a deeply-submerged sphere. Inner lobe structures, of opposite sense to the primary lobes, were also observed in all cases, and it is proposed that the primary and inner lobe structures are formed by the wall jet deforming vorticity shed by the obstacle into a hairpin-like loop. Wavelet analysis of velocity time series on both sides of the wake revealed approximately antisymmetric vortex shedding in the ellipsoid wakes; however, intermittent in-phase shedding was observed in the wake of the sphere. Spectral analyses confirmed the approximate ReDm dependence of the Kelvin-Helmholtz (KH) instability frequency fKH with values of m varying between 0.46 and 0.49. This study showed that the shape of the obstacle junction (convex vs. flat) plays an important role in the behavior of the wake.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Flow patterns around confined low-aspect-ratio obstacles

Hajimirzaie

Buchholz

2023

Preprint

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Solid-flow interactions of a large aspect ratio cylinder in a shallow open channel

et al. 2020

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The complex wake created by an emergent slender circular cylinder in a shallow open channel flow is studied at a cylinder Reynolds number (ReD) of 3300 and at a subcritical Froude number of 0.58 in water. Methodical laser Doppler velocimetry measurements were taken in a very fine grid in three horizontal planes at near bed, mid-depth, and near free surface both upstream and downstream of the cylinder. Demarcation of the entire wake region starting from the first point of the onset of disturbed flow upstream to undisturbed flow downstream entirely based on experiments successfully added a novel contribution to the research on wake flow over a single cylinder. The proximity of the bed and free surface has a significant effect on the structure of the wake compared to the mid-depth. The size, shape, and development of the recirculation region behind the cylinder vary in the vertical direction from the bed to free surface. The longest wake closure point was found in the near bed region and the shortest was found near the free surface. The new model developed pertinent to longitudinal velocity deficit can be used as a velocity deficit scale for the entire far wake region for shallow wakes at mid-depth and near free surface. Urms/Us profiles along the transverse direction initially show a double peak behavior for all three levels, and well away from the cylinder downstream, the double peak becomes broader and less distinct, which is attributed to the effect of the separating shear layers. It is also noted that the wake characteristics of slender cylinders are significantly different from those of wakes generated by cylinders with small aspect ratios.

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Flow structure in the wake of a low-aspect-ratio wall-mounted bluff body

Cited by 2 publications

References 93 publications

Flow patterns around confined low-aspect-ratio obstacles

Flow patterns around confined low-aspect-ratio obstacles

Solid-flow interactions of a large aspect ratio cylinder in a shallow open channel

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