Bursting process of large- and small-scale structures in turbulent boundary layer perturbed by a cylinder roughness element

Tang, Zhizhong; Jiang, Nan; Zheng, Xing; Wu, Yanhua

doi:10.1007/s00348-016-2174-0

Cited by 30 publications

(29 citation statements)

References 48 publications

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“…In Figure 2, the mean velocity profiles measured using single hot wire are consistent with those measured by 2D hot wire. Besides, the velocity profile over the smooth surface agrees well with laws of the wall reported in previous studies (U+=(1/0.41)lny++5.0 34,35 ). A broad logarithmic region is present (y+≈35∼380), confirming that the experiment was performed at a reasonably large Reynolds number.…”

Section: Resultssupporting

confidence: 89%

“…Later, Tang et al. 35 studied the bursting process of large- and small-scale structures in a cylinder-roughness-element perturbed boundary layer by calculating the bursting duration, period and frequency. The results indicated that the large-scale bursting process also imposes a modulation on the bursting events of small-scale fluctuations.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of large- and small-scale structures in the turbulent boundary layer over a drag-reducing riblet surface

Zhang

Cai

Cheng

2019

Proceedings of the Institution of Mechanical Engineers, Part C:

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Riblet is one of the most promising passive drag reduction techniques in turbulent flows. In this paper, hot-wire measurements on a turbulent boundary layer perturbed by a drag-reducing riblet surface are carried out to further understand the riblet effects on the turbulent flows and the drag reduction mechanism. Compared with the smooth case, different energy variations in the near-wall region and the logarithmic region are observed over riblets. Then, by using a spectral filter of a given wavelength, the time series of the hot-wire data are decomposed into large- and small-scale components. It is indicated that large-scale structures in the logarithmic region impose a footprint (amplitude modulating effect) on the near-wall small-scale structures. By quantifying this footprint, it is found that the interactions between large- and small-scale structures over riblets are weakened in the near-wall region. Furthermore, the bursting process of large and small scales is studied. For both large- and small-scale structures, a shorter bursting duration and a higher bursting frequency are observed over the riblet surface, which indicates that riblets impede the formation of large- and small-scale bursting events. The flow physics behind these phenomena are also discussed in detail.

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Section: Resultssupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

Characteristics of large- and small-scale structures in the turbulent boundary layer over a drag-reducing riblet surface

Zhang

Cai

Cheng

2019

Proceedings of the Institution of Mechanical Engineers, Part C:

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“…Pitot probes were used to measure the wall pressures along five streamwise positions. The corresponding data acquisition frequency was 200 Hz and the sample length was 10 s. By adjusting the inclination angle of the plate using four high-precision micrometers, the pressures along the streamwise positions kept constant, implying that the turbulent flow was under the zero pressure gradient condition (Marusic et al (2015), Tang et al (2016)). In order to keep a constant incoming flow, the test plate was di-vided into two halves [see Fig.…”

Section: Methodsmentioning

confidence: 99%

“…These observations could be seen that riblets disassembled and redistributed the near-wall turbulent streaks. The disassembled turbulent streaks would undoubtedly disturb the distribution of turbulent energy and thereafter influence the bursting process in the near-wall viscous region (Tang et al (2016), Hutchins and Marusic (2007), Bentley (2004)). Therefore, the pre-multiplied energy spectra, same as the one described in section 3.1, was analyzed.…”

Section: Fig 7 Typical Comparisons Between Experimental and Numericmentioning

confidence: 99%

Investigation on the Mechanism of Drag Modification over Triangular Riblets

Zhang¹,

Zhang²,

Zhao³

2020

JAFM

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This paper presents experimental and numerical investigations on the modification of local spanwise skinfriction over triangular riblets under the total drag reduction condition. Specifically, the mean and fluctuating vortical flow fields were measured using 2-components X-wires and computed using LES, respectively. Besides, the relationship between local skin-friction along the riblet spanwise and associated vortex evolution was also built using the vortex dynamic method. Based on these results, it was found that, compared with the smooth case, the impaired and enhanced vortex strength, and resultant viscous diffusion/energy dissipation, determined the reduction and augment of the viscous drag force over the local spanwise riblet groove, i.e., decreasing and increasing cases of local drag, respectively. Furthermore, the mean normal diffusion fluxes of normal and spanwise vorticities contributed more to the viscous drag under these two cases. Correspondingly, the relevant flow physics related to these phenomena was discussed in detail.

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“…Numerous passive and active control methods have been developed based on this flow mechanism [12]. As a representative of the passive control methods, Wash and Choi et al [13][14][15] achieved considerable drag reduction on riblet surfaces by conducting experiments and direct numerical simulations. In comparison with the passive control method, the active control method has wider adaptability to complex flows, and it enhances the control effectiveness [16][17][18][19], which has been confirmed by several experimental and simulation investigations [20][21][22][23][24][25][26][27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Active control of multiscale features in wall-bounded turbulence

et al. 2019

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This study experimentally investigates the impact of a single piezoelectric (PZT) actuator on a turbulent boundary layer from a statistical viewpoint. The working conditions of the actuator include a range of frequencies and amplitudes. The streamwise velocity signals in the turbulent boundary layer flow are measured downstream of the actuator using a hot-wire anemometer. The mean velocity profiles and other basic parameters are reported. Spectra results obtained by discrete wavelet decomposition indicate that the PZT vibration primarily influences the near-wall region. The turbulent intensities at different scales suggest that the actuator redistributes the near-wall turbulent energy. The skewness and flatness distributions show that the actuator effectively alters the sweep events and reduces intermittency at smaller scales. Moreover, under the impact of the PZT actuator, the symmetry of vibration scales' velocity signals is promoted and the structural composition appears in an orderly manner. Probability distribution function results indicate that perturbation causes the fluctuations in vibration scales and smaller scales with high intensity and low intermittency. Based on the flatness factor, the bursting process is also detected. The vibrations reduce the relative intensities of the burst events, indicating that the streamwise vortices in the buffer layer experience direct interference due to the PZT control.

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Bursting process of large- and small-scale structures in turbulent boundary layer perturbed by a cylinder roughness element

Cited by 30 publications

References 48 publications

Characteristics of large- and small-scale structures in the turbulent boundary layer over a drag-reducing riblet surface

Characteristics of large- and small-scale structures in the turbulent boundary layer over a drag-reducing riblet surface

Investigation on the Mechanism of Drag Modification over Triangular Riblets

Active control of multiscale features in wall-bounded turbulence

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