Re-examination of the effect of a plane boundary on force and vortex shedding of a circular cylinder

Lei, Chengwang; Cheng, Liang; Kavanagh, Kenneth

doi:10.1016/s0167-6105(98)00204-9

Cited by 254 publications

(203 citation statements)

References 14 publications

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“…As concerns the influence of the boundary layer, Zdravkovich 11 reported that the rapid decrease in drag occurred as the gap was reduced to less than the thickness of the boundary layer, ␦ B , on a fixed ground, and concluded that the variation of the drag coefficient was dominated by h / ␦ B rather than by the conventional gap ratio h / d. However, Hiwada et al 12 reported, for the case of ␦ B / d = 0.23, that the decrease in drag started around h / d = 0.5, at which the cylinder was still outside the thin wall boundary layer and the regular vortex shedding was still observed. A further investigation was conducted for a wider range of ␦ B / d by Lei et al, 13 but no clear relation was observed between ␦ B , ͑h / d͒ c and the gap at which the decrease in drag occurred in their measurements. More recently, Zdravkovich 14 measured the drag on a circular cylinder placed near a moving ground at a higher Reynolds number of 2.5ϫ 10, 5 and reported that, in contrast to all the above investigations, the decrease in drag due to the decrease in h / d did not occur.…”

Section: ͔ Bearman and Zdravkovichmentioning

confidence: 92%

Vortex shedding from a circular cylinder near a moving ground

2007

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The flow and force characteristics have been experimentally investigated of a circular cylinder with an aspect ratio of 8.33, with and without end-plates, placed near and parallel to a moving ground, on which substantially no boundary layer developed to interfere with the cylinder. Mean drag and lift measurements, surface oil flow visualization, and particle image velocimetry ͑PIV͒ measurements were carried out at two upper-subcritical Reynolds numbers of 0.4 and 1.0ϫ 10 5 ͑based on the cylinder diameter d͒ to investigate the mechanisms of the ground effect, i.e., the effect of the gap-to-diameter ratio h / d, where h is the gap between the cylinder and the ground. For the cylinder with end-plates, on which the oil flow patterns were observed to be essentially two-dimensional, the drag rapidly decreased as h / d decreased to less than 0.5 but became constant for h / d of less than 0.35, unlike that usually observed near a fixed ground. This critical drag behavior was found to be directly related to a global change in the near wake structure of the cylinder; as h / d decreased the Kármán-type vortex shedding became intermittent at h / d = 0.4, and then totally ceased and instead two nearly parallel shear layers were formed behind the cylinder at h / d = 0.3 and below. For the cylinder without end-plates, however, no such critical change in drag was observed as the Kármán-type vortices were not generated in the near wake region at all h / d investigated. Based on the experimental results obtained, further discussions are also given to the essential cause of the cessation of the Kármán vortex shedding in the ground effect.

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Section: ͔ Bearman and Zdravkovichmentioning

confidence: 92%

Vortex shedding from a circular cylinder near a moving ground

2007

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“…When water must pass through a constricted opening (the gap), the velocity increases and the pressure decreases; the decreased pressure under the piece causes a downward force. Gap lift coefficients can be estimated from Lei et al [1999] as…”

Section: Interactions With the Flowmentioning

confidence: 99%

Factors influencing wood mobilization in streams

Merten

Finlay

Johnson³

et al. 2010

Water Resources Research

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[1] Natural pieces of wood provide a variety of ecosystem functions in streams including habitat, organic matter retention, increased hyporheic exchange and transient storage, and enhanced hydraulic and geomorphic heterogeneity. Wood mobilization is a critical process in determining the residence time of wood. We documented the characteristics and locations of 865 natural wood pieces (>0.05 m in diameter for a portion >1 m in length) in nine streams along the north shore of Lake Superior in Minnesota. We determined the locations of the pieces again after an overbank stormflow event to determine the factors that influenced mobilization of stationary wood pieces in natural streams. Seven of 11 potential predictor variables were identified with multiple logistic regression as significant to mobilization: burial, effective depth, ratio of piece length to effective stream width (length ratio), bracing, rootwad presence, downstream force ratio, and draft ratio. The final model (P < 0.001, r 2 = 0.39) indicated that wood mobilization under natural conditions is a complex function of both mechanical factors (burial, length ratio, bracing, rootwad presence, draft ratio) and hydraulic factors (effective depth, downstream force ratio). If stable pieces are a goal for stream management then features such as partial burial, low effective depth, high length relative to channel width, bracing against other objects (e.g., stream banks, trees, rocks, or larger wood pieces), and rootwads are desirable. Using the model equation from this study, stewards of natural resources can better manage in-stream wood for the benefit of stream ecosystems.

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“…doi:10. /j.jfluidstructs.2007 The flow around a circular cylinder placed near and parallel to a ground has been experimentally investigated by Bearman and Zdravkovich (1978), Zdravkovich (1985), Lei et al (1999), and the present authors , among others [see for a more extensive review]. The characteristics of the flow and force acting on the cylinder in this case are governed not only by the Reynolds number Re but also by the gap ratio, i.e., the ratio of the distance between the cylinder and the ground, h, to the cylinder diameter d (Bearman and Zdravkovich, 1978).…”

Section: Article In Pressmentioning

confidence: 99%

“…The characteristics of the flow and force acting on the cylinder in this case are governed not only by the Reynolds number Re but also by the gap ratio, i.e., the ratio of the distance between the cylinder and the ground, h, to the cylinder diameter d (Bearman and Zdravkovich, 1978). However, the mechanisms of the flow and force variations caused by different h/d, or 'ground effect', are in general rather complicated since they can be significantly affected by the state of the boundary layer formed on the ground (Zdravkovich, 1985;Lei et al, 1999). Hence the present authors recently carried out a series of experiments on a circular cylinder placed near a moving ground running at the same speed as the free-stream (Re ¼ 0.4 and 1.0 Â 10 5 based on the cylinder diameter d) to avoid the confusing effects of the boundary layer and thereby to elucidate the essence of the ground effect .…”

Section: Article In Pressmentioning

confidence: 99%

Unsteady RANS and detached-eddy simulations of flow around a circular cylinder in ground effect

Nishino

Roberts

Zhang

2008

Journal of Fluids and Structures

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Unsteady Reynolds-averaged Navier-Stokes (URANS) simulations and detached-eddy simulations (DES) were performed of flow around a circular cylinder placed near and parallel to a moving ground, on which substantially no boundary layer developed to interfere with the cylinder. The results were compared with experiments previously reported by the authors to examine how accurately the URANS and DES can predict the cessation of von Ka´rma´n-type vortex shedding and the attendant critical drag reduction of the cylinder in ground effect. The DES, which were performed in a three-dimensional domain with spanwise periodicity imposed, correctly captured the cessation of the vortex shedding, whereas both two-and three-dimensional URANS also predicted it but at a much smaller gapto-diameter ratio compared with the experiments. The wake structures of the cylinder predicted by the DES were in good agreement with the experiments in both large-and small-gap regimes, and also in the intermediate-gap regime, where the DES captured the intermittence of the vortex shedding in the near-wake region. Based on the results obtained, further discussions are also given to the reason why the von Ka´rma´n-type vortices in the URANS solutions incorrectly 'survived' until the cylinder came much closer to the ground. r

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Re-examination of the effect of a plane boundary on force and vortex shedding of a circular cylinder

Cited by 254 publications

References 14 publications

Vortex shedding from a circular cylinder near a moving ground

Vortex shedding from a circular cylinder near a moving ground

Factors influencing wood mobilization in streams

Unsteady RANS and detached-eddy simulations of flow around a circular cylinder in ground effect

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