POD analysis of the instability mode of a low-speed streak in a laminar boundary layer

Deng, Si-Chao; Pan, Chong; Wang, Jinjun; Rinoshika, Akira

doi:10.1007/s10409-017-0681-8

Cited by 5 publications

(5 citation statements)

References 38 publications

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“…1993; Chatterjee 2000; Zhang, Liu & Wang 2014; Deng et al. 2017). For flow over a bluff body, it has been proved that the first two POD modes, which are closely related to the von Kármán vortex street (Ma, Karamanos & Karniadakis 2000; Perrin et al.…”

Section: Resultsmentioning

confidence: 99%

“…The purpose of this method is actually to find an optimal low-dimensional approximation of the high-dimensional system. The modes are ranked in descending order of energy (Sirovich 1987;Berkooz et al 1993;Chatterjee 2000;Zhang, Liu & Wang 2014;Deng et al 2017). For flow over a bluff body, it has been proved that the first two POD modes, which are closely related to the von Kármán vortex street (Ma, Karamanos & Karniadakis 2000;Perrin et al 2006Perrin et al , 2007, make a dominant contribution to the total energy, e.g.…”

Section: Resultsmentioning

confidence: 99%

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Effect of excitation frequency on flow characteristics around a square cylinder with a synthetic jet positioned at front surface

Wang

Feng

et al. 2019

J. Fluid Mech.

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The flow over a square cylinder controlled by a slot synthetic jet positioned at the front surface is investigated experimentally at different excitation frequencies. The Reynolds number based on the free-stream velocity and the side length of the square cylinder is 1000. The flow visualization was conducted using the laser-induced fluorescence technique. The velocity fields upstream and downstream of the square cylinder were measured synchronously with the two-dimensional time-resolved particle image velocimetry technique. Both the evolution of vortex structures and the characteristic frequencies of upstream and downstream flow fields are presented. The flow dynamics vary significantly with the excitation frequency at a fixed stroke length. During one excitation cycle, the synthetic jet vortex pair deflects to one side and later swings to the other side at a quite small excitation frequency of $f_{e}/f_{0}=0.6$, while it only deflects toward one side and does not turn to the other side at $f_{e}/f_{0}=1.0$. Compared with the natural case, the wake characteristics for the above two cases are not changed much by the synthetic jet adopted. At a moderate excitation frequency of $f_{e}/f_{0}=2.0$, the synthetic jet deflects upwards and downwards alternatively. The upstream flow field has a dominant frequency identical to half of the excitation frequency. Under the perturbations of the synthetic jet, two wake vortex pairs are formed per shedding cycle with a shedding frequency equal to that of the square cylinder without control. At a higher excitation frequency of $f_{e}/f_{0}=3.4$, the synthetic jet keeps deflecting to one side, and the upstream flow field is governed by the excitation frequency. The flow separation on the deflected side is suppressed effectively, and no periodic vortex shedding can be observed in the wake. Statistically, the velocity profiles also change with control. The recirculation bubble length in the wake is shortened, and the time-averaged velocity fluctuation is weakened remarkably. The control effects of the synthetic jet and the continuous jet are compared in this paper when placed at the front surface of a square cylinder.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Effect of excitation frequency on flow characteristics around a square cylinder with a synthetic jet positioned at front surface

Wang

Feng

et al. 2019

J. Fluid Mech.

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“…The POD method provides a series of orthonormal basis and temporal coefficients by spanning the entire data set. The reconstruction of the velocity fields can be obtained through the linear combination of the spatial modes and temporal coefficients (Deng et al 2017). Hence, the coefficients are related to the contribution of the modes to the flow structures.…”

Section: Variations Of Streaky Structures For Both Fluids In Pod Mode...mentioning

confidence: 99%

“…The velocity fields in streamwise-spanwise plane for single-phase fluid (without micro-bubbles) and mixed fluid (with micro-bubbles) in the near wall region of channel turbulence are measured by using particle image velocimetry (PIV). The dominating flow behavior is extracted by using the proper orthogonal decomposition (POD) method (Wei et al 2016, Deng et al 2017. The energy contents and the coefficients corresponding to different POD modes are discussed.…”

Section: Introductionmentioning

confidence: 99%

Proper orthogonal decomposition analysis on longitudinal streaks in channel flow laden with micro-bubbles

et al. 2019

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The streaky structures in the fluid laden with and without micro-bubbles of channel turbulent boundary layer flow were experimentally studied by using particle image velocimetry technique at a Reynolds number of Re=9.3×10 4 . Micro-bubbles were produced by the electrolysis of water through platinum wires in a low speed circulating water tunnel. The velocity fields in the streamwise-spanwise plane were obtained at three different heights (i.e. y=3 mm, 5 mm and 7 mm) along the wall-normal direction. The two-point autocorrelation of velocity fluctuations was carried out to identify the scale of the streaky structures in the physical space statistically. The proper orthogonal decomposition (POD) method was employed to analyze the turbulent kinetic energy contents and the streaky structures in mode space. The results show that the streak intensity is decreased and the structures become indistinct in the presence of micro-bubbles at a relatively lower height of the boundary layer in physical space. The ratios of the energy corresponding to leading-order modes to the total energy of the turbulent for the mixed fluid (fluid laden with microbubbles) are smaller than those for the single-phase fluid (fluid without microbubbles) at these three heights. The effect on the energy content is decayed with the increase of POD mode number as well as the normal height in POD mode space for the mixed fluid. Through comparing the streaky and non-streaky turbulent activities in the presence of micro-bubbles, it is found that the streaky | The Japan Society of Fluid Mechanics Fluid Dynamics Research Fluid Dyn. Res. 51 (2019) 035504 (21pp)

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“…Thus, the multiscale analysis of stirred flow field is a helpful way to understand the mixing mechanism. Proper orthogonal decomposition (POD) is a multiscale analysis method to study the flow characteristics 5–8 . The previous investigation focused on the extraction flow patterns with high‐energy in stirred flow field 9–12 .…”

Section: Introductionmentioning

confidence: 99%

Effects of baffle on cycle‐to‐cycle variation in stirred vessel driven by paddle turbine using quadruple proper orthogonal decomposition

Fan

Sun

Gao

et al. 2021

Asia-Pacific J Chem Eng

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The flow of stirring process is complex and multiscale. To analyze the effects of baffle on the flow characteristics driven by paddle turbine, particle image velocimetry (PIV) experiments were performed for the unbaffled stirred vessel and the standard baffled stirred vessel stirred by the single paddle turbine. Under the baffle arrangement, the flow discharge was strengthened, and the range of high‐velocity region was obviously expanded, and the velocity significantly fluctuated near the blade. The swirling intensity behind the blade decreased significantly, and no significant wake structure was formed, thereby helping reduce the local velocity difference attributed to the wake structure and facilitate the uniform mixing of materials. The instantaneous velocity field was decomposed into four parts at different scales by employing quadruple Proper Orthogonal Decomposition method. The quantitative analysis of different scale flow structures in stirred process was realized. Under the baffle arrangement, the flow process was facilitated in the measurement plane. In addition, the fluctuation velocity increased significantly, and the mass transfer was enhanced by vortex motion of the fluid elements, which was conducive to the uniform mixing of materials.

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POD analysis of the instability mode of a low-speed streak in a laminar boundary layer

Cited by 5 publications

References 38 publications

Effect of excitation frequency on flow characteristics around a square cylinder with a synthetic jet positioned at front surface

Effect of excitation frequency on flow characteristics around a square cylinder with a synthetic jet positioned at front surface

Proper orthogonal decomposition analysis on longitudinal streaks in channel flow laden with micro-bubbles

Effects of baffle on cycle‐to‐cycle variation in stirred vessel driven by paddle turbine using quadruple proper orthogonal decomposition

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