Influence of wall proximity on characteristics of wake behind a square cylinder: PIV measurements and POD analysis

Shi, Liu; Liu, Ying Zheng; Wan, Jin

doi:10.1016/j.expthermflusci.2009.08.008

Cited by 79 publications

(23 citation statements)

References 20 publications

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“…Note that for this figure, the coordinate x is measured from the leading edge of the cylinder. recirculation bubbles; a similar effect was noted by Shi et al (2010) for the case of g=D ¼ 0:2 When the cylinder is located directly on the bottom wall, the secondary cell on the wall merges with the top recirculation bubble to form a single large vortical cell behind the obstacle, together with a weaker secondary recirculation zone in the corner created by the rear face of the cylinder and bottom wall. For this geometry, the bottom recirculation bubble in the wake is completely suppressed by the wall, Fig.…”

Section: Studysupporting

confidence: 50%

“…This critical gap ratio was previously documented by Bosch et al (1996) as g=D ¼ 0:35 À 0:5, by Durao et al (1991) as g=D ¼ 0:35, and later by Martinuzzi et al (2003) as g=D ¼ 0:3 based on measurements of the pressure fluctuations for different gap ratios. Shi et al (2010) performed standard and time-resolved PIV measurements of flow over a square cylinder for a range of gap ratios (0.1-0.8) at a Reynolds number of Re ¼ 2250, and also used Proper Orthogonal Decomposition (POD) to analyze the energetic structures in the wake. In the limiting case when the square cylinder rests directly on the wall, then the cylinder represents a single prismatic rib.…”

Section: Introductionmentioning

confidence: 99%

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Effect of a wall on the wake dynamics of an infinite square cylinder

Samani

Bergstrom

2015

International Journal of Heat and Fluid Flow

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Section: Studysupporting

confidence: 50%

Section: Introductionmentioning

confidence: 99%

Effect of a wall on the wake dynamics of an infinite square cylinder

Samani

Bergstrom

2015

International Journal of Heat and Fluid Flow

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“…The proper orthogonal decomposition (POD) is nowadays a well established mathematical procedure that has been largely used for the detection of coherent structures embedded within the flows (see, for example [12,13]), and recently has also been applied to obtain phase-averaged velocity fields (e.g., [14][15][16]). In the present paper, time-resolved particle image velocimetry (TR-PIV) measurements describing the flow field in a highly loaded LPT cascade have been analyzed with the aim of identifying, splitting and characterizing the different phenomena producing losses.…”

Section: Introductionmentioning

confidence: 99%

A POD-Based Procedure for the Split of Unsteady Losses of an LPT Cascade

Lengani

Simoni

Ubaldi

et al. 2017

IJTPP

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A time-resolved particle image velocimetry (TR-PIV) system has been employed to investigate the unsteady propagation of upstream wakes in a low-pressure turbine cascade. Data are obtained in the steady state condition and for two passing wake reduced frequencies. The study is focused on the identification and split of the different dynamics responsible for deterministic and random oscillations, thus loss generation by means of a new procedure based on proper orthogonal decomposition (POD). The paper takes advantage of the properties of POD that reduce the data set to a low number of modes that represent the most energetic dynamics of the system. It is clearly shown that the phase averaged flow field can be represented by a few number of POD modes related to the wake passing event for the unsteady cases. Proper orthogonal decomposition is also able to capture flow features affecting the instantaneous flow field not directly related to the wake passage (i.e., the vortex shedding phenomenon induced by the intermittent separation developing between adjacent wakes), which are smeared out in the phase averaged results. A procedure exploiting the biorthogonality condition of the POD modes, and the related temporal coefficients, has been developed for the quantification of the contribution due to the different POD modes to the overall turbulence kinetic energy production, or, equivalently, the mean flow energy dissipation rate. Results into the paper clearly show that losses due to wake migration, boundary layer and vortex shedding related phenomena can be distinguished and separately quantified for the different tested conditions.

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“…Furthermore, the application of proper orthogonal decomposition (POD) method in conjunction with field-measurement techniques like PIV in area of coherent structures has been increased significantly recently [100]. POD can be used in analysis of experimental or high-dimensional systems data to extract 'mode shapes' or basis functions.…”

Section: Introductionmentioning

confidence: 99%

“…Perrin [100] have studied broad investigations on POD applications on flow field characteristics around cylinder. In case of foam-covered cylinder which the flow contains large-scale and complex structures, POD can extract dominant structures and flow pattern based on the turbulence kinetic energy [99].…”

Section: Introductionmentioning

confidence: 99%

Wake behind a rough (metal foam-covered) cylinder in cross-flow

Abdi¹

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The flow structures behind a circular cylinder are associated with various instabilities. These instabilities are characterized by the Reynolds number and they include the wake, separated shear layer and boundary layer. Depending on the physical application of the cylinder, increasing the level of turbulence by wrapping the cylinder with metal foam would be a target for drag reduction or heat transfer enhancement.In contrast to the extensive consideration that has been devoted to the flow around bare cylinders, the flow structures around the foam-covered cylinders and the characteristics of the wake behind such surfaces has received relatively little attention. Since the present study explores the possibility of using metal foams as replacements for fins on heat exchanger tubes, investigation on the flow-field structures downstream of a foam-covered cylinder and compare it to the bare cylinder specifies the feasibility of using the foamcovered cylinders in heat exchangers. Moreover, the outcome of this study can be used to develop an appropriate boundary condition for the porous-air interface modelling also increases the knowledge of turbulence in porous media.As it will be discussed more in detail in the following chapters, pressure drop and drag coefficient are directly linked to the wake and recirculation region, and to study these two phenomena, it is necessary to have in depth study on the flow-field down-stream of the cylinder. Hence, the purpose of this study is to investigate the wake region behind a foam- Moreover, using hot-wire anemometry, to investigate the energy of the flow inside and outside of the foam-covered cylinder's wake, let us know if a foam-covered cylinder can be treated as an obstacle to the incident flow with a rough surface or the whole foam can be considered as the combination of local jets that are coming out of the pores and disperse in random directions.III

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Influence of wall proximity on characteristics of wake behind a square cylinder: PIV measurements and POD analysis

Cited by 79 publications

References 20 publications

Effect of a wall on the wake dynamics of an infinite square cylinder

Effect of a wall on the wake dynamics of an infinite square cylinder

A POD-Based Procedure for the Split of Unsteady Losses of an LPT Cascade

Wake behind a rough (metal foam-covered) cylinder in cross-flow

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