Experimental investigation of a three-dimensional bluff-body wake

Ahmed, Anwar; Khan, Mohammad Javed; Bays‐Muchmore, Byram

doi:10.2514/3.11365

Cited by 67 publications

(16 citation statements)

References 8 publications

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“…In the recent few years, several types of cylinders with surface profile varying sinusoidally along their spanwise direction, named wavy cylinders, were introduced (see figure 1). Ahmed & Bays-Muchmore (1992), Ahmed, Khan & Bays-Muchmore (1993), Tombazis & Bearman (1997), Bearman & Owen (1998), Owen, Szewczyk & Bearman (2000), Darekar & Sherwin (2001a, b), Keser et al (2001), Lam et al (2004), Lam, Wang & So (2004), Zhang, Dai & Lee (2005), Dobre, Hangan & Vickery (2006), Lee & Nguyen (2007) and Lam & Lin (2007, 2008 have investigated various types of wavy objects experimentally and numerically under different flow conditions. Their studies are summarized in table 1.…”

Section: Introductionmentioning

confidence: 99%

“…They found that the separated flow structures near the geometric nodes are distinctly asymmetric for a large fraction of time, and the sectional drag coefficients at the geometric nodes are greater than that at the geometric saddle. Ahmed et al (1993) further investigated experimentally the turbulent wake behind a wavy cylinder. They described the topology of the boundary layer separation lines and the subsequent three-dimensional development of turbulent structure of the wake.…”

Section: Introductionmentioning

confidence: 99%

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Effects of wavelength and amplitude of a wavy cylinder in cross-flow at low Reynolds numbers

2009

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Three-dimensional numerical simulations of laminar flow around a circular cylinder with sinusoidal variation of cross-section along the spanwise direction, named ‘wavy cylinder’, are performed. A series of wavy cylinders with different combinations of dimensionless wavelength (λ/Dm) and wave amplitude (a/Dm) are studied in detail at a Reynolds number of Re = U∞Dm/ν = 100, where U∞ is the free-stream velocity and Dm is the mean diameter of a wavy cylinder. The results of variation of mean drag coefficient and root mean square (r.m.s.) lift coefficient with dimensionless wavelength show that significant reduction of mean and fluctuating force coefficients occurs at optimal dimensionless wavelengths λ/Dm of around 2.5 and 6 respectively for the different amplitudes studied. Based on the variation of flow structures and force characteristics, the dimensionless wavelength from λ/Dm = 1 to λ/Dm = 10 is classified into three wavelength regimes corresponding to three types of wake structures. The wake structures at the near wake of different wavy cylinders are captured. For all wavy cylinders, the flow separation line varies along the spanwise direction. This leads to the development of a three-dimensional free shear layer with periodic repetition along the spanwise direction. The three-dimensional free shear layer of the wavy cylinder is larger and more stable than that of the circular cylinder, and in some cases the free shear layer even does not roll up into a mature vortex street behind the cylinder. As a result, the mean drag coefficients of some of the typical wavy cylinders are less than that of a corresponding circular cylinder with a maximum drag coefficient reduction up to 18%. The r.m.s. lift coefficients are greatly reduced to practically zero at optimal wavelengths. In the laminar flow regime (60 ≤ Re ≤ 150), the values of optimal wavelength are Reynolds number dependent.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effects of wavelength and amplitude of a wavy cylinder in cross-flow at low Reynolds numbers

2009

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“…Ahmed & Bays-Muchmore (1992) and Ahmed, Khan & Bays-Muchmore (1993) investigated experimentally the pressure field and flow patterns over a wavy cylinder. Lam et al (2004a) and Lam, Wang & So (2004b) performed experiments to deal with the drag reduction and the relevant flow-induced vibration for different wavy cylinders.…”

Section: Introductionmentioning

confidence: 99%

Large-eddy simulation of the compressible flow past a wavy cylinder

Chen

2010

J. Fluid Mech.

120

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Numerical investigation of the compressible flow past a wavy cylinder was carried out using large-eddy simulation for a free-stream Mach number M∞ = 0.75 and a Reynolds number based on the mean diameter Re = 2 × 105. The flow past a corresponding circular cylinder was also calculated for comparison and validation against experimental data. Various fundamental mechanisms dictating the intricate flow phenomena, including drag reduction and fluctuating force suppression, shock and shocklet elimination, and three-dimensional separation and separated shear-layer instability, have been studied systematically. Because of the passive control of the flow over a wavy cylinder, the mean drag coefficient of the wavy cylinder is less than that of the circular cylinder with a drag reduction up to 26%, and the fluctuating force coefficients are significantly suppressed to be nearly zero. The vortical structures near the base region of the wavy cylinder are much less vigorous than those of the circular cylinder. The three-dimensional shear-layer shed from the wavy cylinder is more stable than that from the circular cylinder. The vortex roll up of the shear layer from the wavy cylinder is delayed to a further downstream location, leading to a higher-base-pressure distribution. The spanwise pressure gradient and the baroclinic effect play an important role in generating an oblique vortical perturbation at the separated shear layer, which may moderate the increase of the fluctuations at the shear layer and reduce the growth rate of the shear layer. The analysis of the convective Mach number indicates that the instability processes in the shear-layer evolution are derived from oblique modes and bi-dimensional instability modes and their competition. The two-layer structures of the shear layer are captured using the instantaneous Lamb vector divergence, and the underlying dynamical processes associated with the drag reduction are clarified. Moreover, some phenomena relevant to the compressible effect, such as shock waves, shocklets and shock/turbulence interaction, are analysed. It is found that the shocks and shocklets which exist in the circular cylinder flow are eliminated for the wavy cylinder flow and the wavy surface provides an effective way of shock control. As the shock/turbulence interaction is avoided, a significant drop of the turbulent fluctuations around the wavy cylinder occurs. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the passive control of the compressible flow past a wavy surface.

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“…The wavy trailing edge used by Tombazis and Bearman 10 caused vortex splitting in the wake due to the phase mismatch between two neighboring cells of different shedding frequencies. In the work with wavy circular cylinders, 8,9,12,13 the three-dimensionality was caused by differences in the flow characteristics between the nodal and saddle planes. Lam et al 12 observed that the wake in the formation region of the saddle plane was wider than that of the nodal plane.…”

Section: B Spanwise Forcingmentioning

confidence: 99%

“…Some researchers [7][8][9][10][11][12][13][14] created a geometric boundary condition that varied in the spanwise direction, with the goal of influencing the global wake dynamics. Park et al 7 concluded that variation of the wake width in the spanwise direction forced the Kármán vortex street to lose its twodimensional nature and thus led to vortex dislocations and reduced drag.…”

Section: B Spanwise Forcingmentioning

confidence: 99%

Investigation of the cylinder wake under spanwise periodic forcing with a segmented plasma actuator

Bhattacharya

Gregory

2015

Physics of Fluids

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The wake response to three-dimensional forcing of flow over a circular cylinder was studied. Spanwise-segmented dielectric-barrier discharge plasma actuators were mounted on the cylinder in a square wave pattern for active forcing of the cylinder wake. The buried electrodes were placed periodically to create a spanwise-modulated blowing profile, with the aim of targeting three-dimensional instabilities in the wake. Considerable spanwise variation in the wake was achieved, which was a direct consequence of the difference in the location of shed spanwise vortices from the cylinder, along with the generation of streamwise vorticity. Two distinct power levels were used for forcing the flow, with different flow response observed between the two conditions. With low power, the segmented forcing caused the large-scale spanwise structures in the forcing region to lead those in the no-forcing region, with an accompanying shift away from the centerline and generation of streamwise vorticity. While vortex shedding was not substantially attenuated with low-power forcing, the shedding in the near wake was significantly attenuated with high-power forcing. This attenuation in the shedding strength was accompanied by a decrease in the peak shedding frequency, indicating an increase in the formation length. High-power forcing caused elongation of the Kármán vortices due to the induced strain field and strong differential development of the wake shedding frequency. In both forcing regimes, the wake three-dimensionality increased as shown by the increased width of the spectral peaks.

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Experimental investigation of a three-dimensional bluff-body wake

Cited by 67 publications

References 8 publications

Effects of wavelength and amplitude of a wavy cylinder in cross-flow at low Reynolds numbers

Effects of wavelength and amplitude of a wavy cylinder in cross-flow at low Reynolds numbers

Large-eddy simulation of the compressible flow past a wavy cylinder

Investigation of the cylinder wake under spanwise periodic forcing with a segmented plasma actuator

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