Double-average mean flow and local turbulence intensity profiles from PIV measurements for an open channel flow with rigid vegetation

Martino, Román; Paterson, A.; Piva, M.

doi:10.1007/s10652-011-9221-4

Cited by 13 publications

(10 citation statements)

References 31 publications

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“…This section considers uniform flows through an array of rigid vertical emergent cylinders (cases W and W0). It is important to note that, compared with previous studies of cylinder arrays [19,14,15], the characteristic length of the bed roughness is of the same order of magnitude as the cylinder diameter in this case: k S /D ≈ 0.7, where k S is the equivalent sand grain size of the bed roughness.…”

Section: Cylinder Drag Combined With Bed Frictionmentioning

confidence: 52%

“…The R-ratios for the three test cases are reported in Table 1. Drag forces act as a volume force on the fluid and therefore make the velocity field constant in the vertical direction, except in the near-bed region, where bed friction influences the flow and a boundary layer forms [19,14,15]. The water column can thus be divided into two parts: (1) a region of constant velocity in the upper part of the water column, termed here the constant-velocity region and (2) a boundary layer, defined as the region in which the velocity is variable.…”

Section: Relative Weights Of Bed Friction and Dragmentioning

confidence: 99%

“…Flows through emergent elements, usually vertical cylinder arrays, have been mainly studied under uniform flow conditions [19,14,15]. Flow through an emergent cylinder array is driven by a volume drag force, which generates turbulence throughout the water column.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Combined effects of bed friction and emergent cylinder drag in open channel flow

Dupuis¹,

Proust²,

Berni³

et al. 2016

Environ Fluid Mech

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Open channel flows subjected to a longitudinal transition in roughness, from bed friction to emergent cylinder drag and vice versa, are investigated experimentally in an 18 m long laboratory flume. These are compared to uniform flows subject to (1) bed roughness only and (2) an array of emergent vertical cylinders installed on bed roughness. The nearbed region is investigated in detail for uniform flows through the cylinder array. The water column can be divided into two parts: a region of constant velocity and a boundary layer near the channel bed. In the latter region, a local increase in velocity, or velocity bulge, is observed in line of a cylinder row. The velocity bulge may be related to the disorganization of the von Kármán vortex street by the bed-induced turbulence, resulting in reduced momentum loss in the cylinder wake. The boundary layer height is found to be independent of water depth and bed roughness (smooth or rough bottom). Strong oscillations of the free surface (seiching) are observed. Oscillation amplitude is dependent on the longitudinal position within the cylinder array and is found to decrease with decreasing array length. When water depth/boundary layer height ratio is close to unity, the disorganization of the von Kármán vortex street throughout the water column prevents seiching from occurring. In the case of roughness transition flows, the water depth is found to vary only upstream of the change in roughness. Vertical profiles of velocity and turbulence are self-similar upstream of the transition and collapse with the uniform flow profiles. Downstream of the roughness change, velocity and turbulence vary over a distance of 35 to 50 times the water depth. Roughness transition flows show that seiching is lowered by flow non-uniformity. A 1D momentum equation integrating bed friction and drag force exerted by the cylinder array predicts accurately the water surface profile (0.9 % mean relative error). The computed profiles show that, upstream of the transition, flow depth varies over a distance of about 2600 times the uniform water depth of the upstream roughness. The 1D equation is solved analytically for zero bed friction.

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Section: Cylinder Drag Combined With Bed Frictionmentioning

confidence: 52%

Section: Relative Weights Of Bed Friction and Dragmentioning

confidence: 99%

See 1 more Smart Citation

Combined effects of bed friction and emergent cylinder drag in open channel flow

Dupuis¹,

Proust²,

Berni³

et al. 2016

Environ Fluid Mech

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show abstract

“…Furthermore, this algorithm can run very efficiently, which is desirable when processing large data sets from multiple measuring locations. Lastly, this alignment algorithm is applied to process the velocity data from ADVs, but it is worth noticing that this algorithm is also applicable for other velocity measuring technologies, e.g., EMF (electromagnetic flow manufacture meter) and PIV (particle image velocimetry) [41][42][43].…”

Section: Advantages Of the Current Measuring System And Alignment Algmentioning

confidence: 99%

“…In order to improve the velocity measuring accuracy and reduce the labor involved, PIV system can be applied in future experiments. The PIV system can provide detailed velocity information of velocity field [41,42]. By applying such a system, it is also possible to obtain the relative velocity between water motion and the motion of flexible vegetation stems.…”

Section: Current Limitations and Future Applicationsmentioning

confidence: 99%

Applying a New Force–Velocity Synchronizing Algorithm to Derive Drag Coefficients of Rigid Vegetation in Oscillatory Flows

Yao

Chen

Huang

et al. 2018

Water

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Coastal vegetation is effective in dissipating incident wave energy during storm conditions, which offers valuable protection to coastal communities. Determining vegetation drag coefficient (C D) is of great importance to the quantification of vegetation-induced wave dissipation. Recently, a direct measuring approach has been developed to derive vegetation drag coefficient more accurately compared to the conventional calibration approach. However, as this approach requires perfectly in-phase force and velocity signals, there are two difficulties associated with it. The first difficulty is the availability of a suitable force sensor to compose synchronized force-velocity measuring systems. The second difficulty is related to realigning the obtained timeseries of force and velocity data. This technical note develops a new synchronized force-velocity measuring system by using standard force sensors and an acoustic doppler velocimeter (ADV). This system is applied together with an automatic realignment algorithm to ensure in-phase data for C D deviation. The algorithm reduces the phase shift between force-velocity signals from ca. 0.26 s to 0.003 s. Both time-varying and period-averaged C D can be obtained using this method. The derived C D can be used to accurately reproduce the measured maximum total acting force on vegetation (R 2 = 0.759), which shows the reliability of the automatic alignment algorithm. The newly-developed synchronized force-velocity measuring system and alignment algorithm are expected to be useful in future experiments on vegetation-wave interactions with various hydrodynamic and vegetation settings.

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Experimental investigation of 3D flow properties around emergent rigid vegetation

Kumar

Sharma

2022

Ecohydrology

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The condition of emergent or submerged vegetation plays a vital role in affecting the flow behaviour in open channels. To understand the flow processes in free surface flows under emergent rigid vegetation condition, an extensive experimental investigation is performed in a laboratory channel with staggered combination of emergent rigid vegetation. Three-dimensional velocities data are collected by ADV at various section and position of vegetated channel. The three-dimensional flow properties such as velocity distribution, turbulence intensity, turbulent kinetic energy, Reynolds shear stress in vegetation, and non-disturbed region are analysed and compared with the longitudinal and transverse length of vegetated zone. In the vegetation region, the longitudinal velocity in free stream region decreases as compared with nondisturbed region. However, the vertical velocity also decreases in free stream region except at the centre line of channel cross-section. Variations in velocity in the vegetation section were observed because of the local effect induced by the vegetation stems. Three-dimensional Reynolds shear stress and turbulent intensity were weaker in magnitude at vegetation region. The presence of vegetation reduces the longitudinal profile of flow velocity, Reynolds shear stress and turbulence intensities, which means that vegetation can be used as an effective tool to reduce the flow resistance.The turbulent kinetic energy, skewness and kurtosis are also evaluated and compared between the vegetated and non-vegetated zone. The outcomes of the results provide an important view to understand flow behaviour at immediately front and immediately behind of vegetation stem.

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Double-average mean flow and local turbulence intensity profiles from PIV measurements for an open channel flow with rigid vegetation

Cited by 13 publications

References 31 publications

Combined effects of bed friction and emergent cylinder drag in open channel flow

Combined effects of bed friction and emergent cylinder drag in open channel flow

Applying a New Force–Velocity Synchronizing Algorithm to Derive Drag Coefficients of Rigid Vegetation in Oscillatory Flows

Experimental investigation of 3D flow properties around emergent rigid vegetation

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