The turbulent boundary layer over transverse square cavities

Djenidi, L.; Elavarasan, R.; Antonia, R. A.

doi:10.1017/s0022112099005911

Cited by 133 publications

(79 citation statements)

References 28 publications

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“…Interestingly, the spatial extents of pww in the streawise and spanwise directions appear unaffected by protrusion F as the inhomogeneous correlation matches its homogeneous counterpart except for slight differences for small spatial separations (Note that the inhomogeneous correlations appear much noisier than their homogeneous counterparts because the number of samples averaged to generate inhomogeneous correlations is significantly reduced under this assumption). The relative insensitivity of the larger-scale features of p wl and pe to roughness feature F is consistent with the observations of Djenidi et al (1999) who reported that the outflows from square cavities did not appreciably affect the spatial characteristics of low-speed streaks in the near-wall region. They attributed this insensitivity to the substantial scale difference between the outflows generated by the roughness cavities and the large-scale streaks.…”

Section: Impact Of Surface Protrusions On Spatial Correlations In Rousupporting

confidence: 90%

“…Although the overall shape of Puv was unaffected compared to smooth-wall flow, its streamwise extent was also decreased by the short strip of roughness. Djenidi et al (1999) studied the near-wall structure of a turbulent boundary layer over d-type transverse square cavities using laser-induced fluorescence (LIF) in a streamwise-spanwise plane positioned 6y. above the roughness crests at Reo = 1100.…”

Section: Roughness Effects In the Near-wall Regionmentioning

confidence: 99%

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Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Christensen¹,

Wu²

2008

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The public reporting burden for this collection of information is estimated to average 1 hour per response. including the time for reviewing instructions, sea"hing existing data soUrces, gathering and maintaining the data needed, and completing and reviewving the collection of infomation. Send comments regaliong this burden estimate or any otiler aspect of tts collection of information. including suggestions for reducing fhe burden, to the Department of Defense, Executive Service Directorate (0704-0188). Respondents should be aware that notwithstanding any other provision of law. no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a curently valid OMB control number. PLEASE DO NOT RETURN YOUR A F R L S R SUPPLEMENTARY NOTES ABSTRACTThe present effort investigates the effects of practical roughness replicated from a turbine blade damaged by deposition of foreign material. statistical and structural characteristics of wall turbulence. Two-dimensional particle image velocimetry (PIV) measurements are performed in the streamwise-wall-normal plane of turbulent boundary layers at momentum Reynolds numbers of 8000 and 13000. The surface conditions include a smooth wall and two highly-irregular rough walls. These rough surfaces have the same roughness topography but differ in spatial scaling. The validity of Townsend's wall similarity hypothesis in the presence of practical roughness is assessed and the impact of this roughness on the spatial structure of the flow is investigated. In addition, stereoscopic PIV measurements are made in streamwise-spanwise planes of smooth-and rough-wall turbulent boundary layers both within and at the outer edge of the roughness sublayer. This data is used to explore the impact of dominant topographical features on the near-wall flow as well as the influence of practical roughness on the spatial organization of the flow.Understanding such effects provides a stepping stone toward efficient modeling and control of practical flows in the presence of roughness. SUBJECT TERMS

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Section: Impact Of Surface Protrusions On Spatial Correlations In Rousupporting

confidence: 90%

Section: Roughness Effects In the Near-wall Regionmentioning

confidence: 99%

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Christensen¹,

Wu²

2008

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“…These occurred at irregular time intervals and were associated with some additional air entrainment. The ejections appeared to be sequential from upstream to downstream as illustrated by Djenidi et al (1999) and Chanson et al (2002). On average, the flat stepped data indicated a nearly constant cavity ejection rate independently of downstream distance for a given flow rate (Fig.…”

Section: Cavity Flow Processesmentioning

confidence: 86%

Flow aeration, cavity processes and energy dissipation on flat and pooled stepped spillways for embankments

2013

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The design floods of several reservoirs were recently re-evaluated and the revised spillway outflow could result in dam overtopping with catastrophic consequences for some embankment structures. Herein a physical study was performed on flat and pooled stepped spillways with a slope typical of embankments ( = 26.6°) and four stepped configurations: a stepped spillway with flat horizontal steps, a pooled stepped spillway, and two stepped spillways with in-line and staggered configurations of flat and pooled steps. The focus of the study was on the flow aeration, air-water flow properties, cavity flow processes, and energy dissipation performances. The results demonstrated the strong aeration of the flow for all configurations. On the in-line and staggered configurations of flat and pooled steps, the flow was highly three-dimensional. The residual head and energy dissipation rates at the stepped chute downstream end were calculated based upon the detailed air-water flow properties. The results showed that the residual energy was the lowest for the flat stepped weir. The data for the stepped spillway configuration with in-line and staggered configurations of flat and pooled steps showed large differences in terms of residual head in the transverse direction. Altogether the present results showed that, on a 26.6 slope stepped chute, the designs with in-line and staggered configurations of flat and pooled steps did not provide any advantageous performances in terms of energy dissipation and flow aeration, but they were affected by three-dimensional patterns leading to some flow concentration.

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“…For a flow of given bulk Reynolds number, R, over two-dimensional roughness elements, the transition between d-and k-type roughness depends solely on the streamwise spacing of the elements. Many researchers have chosen to focus on square bar roughness to investigate the effect of spacing on turbulence structure and mean flow characteristics, both experimentally (Coleman, Nikora, McLean, & Schlicke, 2007;Djenidi, Antonia, Amielh, & Anselmet, 2008;Djenidi, Elavarasan, & Antonia, 1999;Krogstad, Andersson, Bakken, & Ashrafian, 2005;Okamoto, Seo, Nakaso, & Kawai, 1993;Roussinova & Balachandar, 2011) and numerically (Cui, Patel, & Lin, 2003;Ikeda & Durbin, 2007;Stoesser & Nikora, 2008;Stoesser & Rodi, 2004). Simpson (1973), Tani (1987), Jiminez (2004) and Coleman et al (2007) all proposed that the transition from d-to k-type roughness occurs at around l/k = 5, where l is the crest-to-crest bar spacing and k is the roughness height.…”

Section: Introductionmentioning

confidence: 99%

Free surface flow over square bars at intermediate relative submergence

McSherry

Chua

Stoesser

et al. 2018

Journal of Hydraulic Research

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Results from large-eddy simulations and complementary flume experiments of turbulent open channel flows over bed-mounted square bars at intermediate submergence are presented. Scenarios with two bar spacings, corresponding to transitional and k-type roughness, and three flow rates, are investigated. Good agreement is observed between the simulations and the experiments in terms of mean free surface elevations and mean streamwise velocities. Contours of simulated time-averaged streamwise, streamfunction and turbulent kinetic energy are presented and these reveal the effect of the roughness geometry on the water surface response. The analysis of the vertical distribution of the streamwise velocity shows that in the lowest submergence cases no logarithmic layer is present, whereas in the higher submergence cases some evidence of such a layer is observed. For several of the flows moderate to significant water surface deformations are observed, including weak and/or undular hydraulic jumps which affect significantly to the overall streamwise momentum balance. Reynolds shear stress, form-induced stress and form drag are analysed with reference to the momentum balance to assess their contributions to the total hydraulic resistance of these flows. The results show that form-induced stresses are dominant at the water surface and can contribute significantly to the overall drag, but the total resistance in all cases is dominated by form drag due to the presence of the bars.

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The turbulent boundary layer over transverse square cavities

Cited by 133 publications

References 28 publications

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Studies of Real Roughness Effects for Improved Modeling and Control of Practical Wall-Bounded Turbulent Flows

Flow aeration, cavity processes and energy dissipation on flat and pooled stepped spillways for embankments

Free surface flow over square bars at intermediate relative submergence

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