POD analysis of a finite-length cylinder near wake

Wang, H. F.; Cao, Huali; Zhou, Yu

doi:10.1007/s00348-014-1790-9

Cited by 82 publications

(13 citation statements)

References 37 publications

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“…Junction flow refers to the interaction of the oncoming boundary layer on the wall with that on the cylinder at their junction. A pair of counter-rotating streamwise vortices is observed on both sides of the cylinder when the junction flow is time averaged (Wang, Cao & Zhou 2014), which are referred to as 'base' or 'junction' vortices. These junction vortices induce upwash in a square FWMC wake, which intensifies with increasing boundary-layer thickness (Wang et al 2006).…”

Section: Introductionmentioning

confidence: 99%

The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders

et al. 2019

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This paper presents a combined experimental and large-eddy simulation study to characterise the effect of aspect ratio on the near-wake structure of a square finite wall-mounted cylinder (FWMC). The cylinder aspect ratios (span $L$ to width $W$) investigated in the experiments were $1.4\leqslant L/W\leqslant 21.4$ and the oncoming boundary-layer thicknesses were $1.3W$ and $0.9W$ at a Reynolds number based on cylinder width of $1.4\times 10^{4}$ and $1.1\times 10^{4}$, respectively. In complementary simulations, the cylinder aspect ratios investigated were 1.4, 4.3, 10 and 18.6. The cylinder wake structure was visualised in three-dimensional space using a vortex core detection method and decomposed to its oscillation modes using the spectral proper orthogonal decomposition (SPOD) technique. A parametric diagram is proposed to predict whether the time-averaged wake structure is a dipole or a quadrupole pattern, based on oncoming boundary-layer height and aspect ratio. Cellular shedding occurs when the aspect ratio is high with up to three shedding cells occurring across the span for aspect ratios $L/W>18$. Each of these cells sheds at a distinct frequency, as evidenced by the spectral content of the surface pressure measured on the side face and the near-wake velocity. Amplitude modulation is also observed in the vortex shedding, which explains the amplitude modulation of the acoustic pressure emitted by square FWMCs. SPOD is shown to be a viable method to identify the occurrence of cellular shedding in the wake.

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Section: Introductionmentioning

confidence: 99%

The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders

et al. 2019

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“…The first two modes of each case (A + C and B + D, respectively) are associated with the von Karman vortex sheet [17], while the third reflects the influence of the tip-induced downwash [13]. This can be demonstrated by flow reconstruction.…”

Section: Resultsmentioning

confidence: 99%

Numerical and experimental investigation of a finite cylinder wake

Leite

Diógenes

Avelar

2019

J Braz. Soc. Mech. Sci. Eng.

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Following a thorough time-resolved 2-D particle image velocimetry experimental investigation of the wake of a square wall-mounted finite cylinder, at Reynolds Re = 5.4 × 10 4 with aspect ratio H/d = 3, a 3-D DNS numerical investigation was performed under similar flow conditions and comparable Reynolds number (Re = 4.0 × 10 4). In this paper, the simulation results in four 2-D planes are compared to the experimental case using proper orthogonal decomposition (POD), spectral analysis and mean flow. Numerical and experimental POD modes were similar, with a few differences in mean flow values and main vortex emission frequency that can be explained by differences in boundary layer thickness. The investigated horizontal planes were z/H = 0.3, z/H = 0.5 and z/H = 1.0 planes, as well as the vertical x-z symmetry plane. While time-resolved experimental results were acquired independently for each investigated plane, numerical results were acquired concomitantly in all four planes, with full 3-D wake data available. The results in this paper confirm that the simulation is able to reproduce the main dynamic features of the flow, establishing the basis for deeper analysis of the full numerical data set in the future. Keywords Cylinder wakes • Finite cylinders • Computational fluid dynamics • Particle image velocimetry • Low speed flow List of symbols d Square cylinder side dt Time step z Cylinder height coordinate H Total cylinder height Re d Reynolds number based on the cylinder side St Strouhal number δ 99% Boundary layer thickness

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“…The POD approach has been widely used to analyze the coherent structures of both pressure and flow fields since it can extract the structures of different scales from random fluctuating fields (Kikuchi et al, 1997;van Oudheusden et al, 2005;Wang et al, 2014). In the present study, the pressure fluctuations at different cylinder spans with the variation of I u and L u x in smooth and turbulent flows were investigated using POD.…”

Section: Pod Analysismentioning

confidence: 99%

Experimental investigation of the effects of free-stream turbulence on aerodynamic characteristics of a 3D square cylinder by pressure measurement and PIV visualization

Shi

et al. 2022

Preprint

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This paper investigates the effects of free-stream turbulence such as longitudinal turbulence intensity (Iu) and integral length scale (Lxu) on the flow fields around, and aerodynamic pressures and forces on a surface-mounted three-dimensional (3D) square cylinder with a height-to-width ratio of 5. The flow fields, aerodynamic pressures and forces were experimentally studied by the particle image velocimetry (PIV) visualizations and pressure measurements in grid-generated turbulent flows and smooth flow. The PIV flow visualizations show that increasing (Lxu) has limited effect on the characteristics of wake flow, except slightly weakens and intensifies the downwash and upwash flows, respectively. The influences of turbulence intensity are noteworthy. The Kármán vortices influence the flow features more significantly in turbulent flows with high intensity. The mean pressures on the side faces of the cylinder decrease as(Iu) increases, but increases on the leeward face. Increasing(Iu) and (Lxu) both enhance the fluctuating lift forces and reduce the mean drag forces at all cylinder spans. The spanwise vortex shedding of the cylinder is respectively enhanced and weakened with increasing ( Iu)and (Lxu)The strong vortex shedding occurs near the cylinder’s mid-span. The analyzed results by Proper orthogonal decomposition (POD) method show the symmetric vortex shedding process on the side faces of the 3D cylinder in smooth flow, resulting in small lift fluctuations. In turbulent flows, the vortex shedding process is symmetric near the free-end, alternating at cylinder’s lower half.

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POD analysis of a finite-length cylinder near wake

Cited by 82 publications

References 37 publications

The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders

The effect of aspect ratio on the wake structure of finite wall-mounted square cylinders

Numerical and experimental investigation of a finite cylinder wake

Experimental investigation of the effects of free-stream turbulence on aerodynamic characteristics of a 3D square cylinder by pressure measurement and PIV visualization

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