Analysis of turbulent flow characteristics in the vicinity of the bar in a braided river model
TL;DR: In this paper, the results of measurements of three-dimensional velocities carried out in a laboratory model of a braided river are presented in order to recognize the structure of Reynolds stresses in turbulent flow near the bar.
Abstract: Turbulent phenomenon in braided rivers is much more complex as compared to the straight and meandering rivers. Turbulent flow characteristics around the braid bar are not thoroughly studied till now. The results of measurements of three-dimensional velocities carried out in a laboratory model of braided river are presented in this paper. Velocity is measured with the help of acoustic Doppler velocimeter. The main purpose of the study is the recognition of structure of Reynolds stresses in turbulent flow near the bar. Sweep quadrant event is considered to be the most important for entrainment of sediment particles as it exerts forces in the flow direction resulting in rolling and sliding of sediment particle. Similarly, the ejection event has been considered important for sediment transport since these events maintain the sediment particles in suspension. Special attention has been given to sweep and ejection bursting events due to their relation with the sediment entrainment and transport. The fra...
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TL;DR: In this article, Lindley et al. make the less restrictive assumption that such a normal, homoscedastic, linear model is appropriate after some suitable transformation has been applied to the y's.
Abstract: [Read at a RESEARCH METHODS MEETING of the SOCIETY, April 8th, 1964, Professor D. V. LINDLEY in the Chair] SUMMARY In the analysis of data it is often assumed that observations Yl, Y2, *-, Yn are independently normally distributed with constant variance and with expectations specified by a model linear in a set of parameters 0. In this paper we make the less restrictive assumption that such a normal, homoscedastic, linear model is appropriate after some suitable transformation has been applied to the y's. Inferences about the transformation and about the parameters of the linear model are made by computing the likelihood function and the relevant posterior distribution. The contributions of normality, homoscedasticity and additivity to the transformation are separated. The relation of the present methods to earlier procedures for finding transformations is discussed. The methods are illustrated with examples.
12,158 citations
"Analysis of turbulent flow characte..." refers background or methods in this paper
...i ) for this situation is given by 11 (Box and Cox 1964)....
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...In order to compute the mean values of sweep and ejection events angle, the data are transformed into normal distribution using the Box–Cox power transformation (Box and Cox 1964)....
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...The inverse transformation B−1 of B ( i ) for this situation is given by 11 (Box and Cox 1964)....
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...(10)B ( i ) = ln ( i + k ) (11) = [ B ( i ) + 1] 1 A Box–Cox power transformation is defined for non-zero values of by Equation (9) (Box and Cox 1964)....
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...i ) + 1] 1 A Box–Cox power transformation is defined for non-zero values of by Equation (9) (Box and Cox 1964)....
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TL;DR: In this article, the accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in a 17m flume using an ADV and a laser DOF.
Abstract: Accuracy of the acoustic Doppler velocimeter (ADV) is evaluated in this paper. Simultaneous measurements of open-channel flow were undertaken in a 17-m flume using an ADV and a laser Doppler velocimeter. Flow velocity records obtained by both instruments are used for estimating the true (“ground truth”) flow characteristics and the noise variances encountered during the experimental runs. The measured values are compared with estimates of the true flow characteristics and values of variance (〈u′2〉, 〈w′2〉) and covariance (〈u′w′〉) predicted by semiempirical models for open-channel flow. The analysis showed that the ADV sensor can measure mean velocity and Reynolds stress within 1% of the estimated true value. Mean velocities can be obtained at distances less than 1 cm from the boundary, whereas Reynolds stress values obtained at elevations greater than 3 cm above the bottom exhibit a variation that is in agreement with the predictions of the semiempirical models. Closer to the boundary, the measure...
566 citations
"Analysis of turbulent flow characte..." refers background in this paper
...High frequency of measurement may induce spike in velocity measurement (Voulgaris and Trowbridge 1998)....
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TL;DR: In this paper, a stability analysis of meandering and braiding perturbations in a model alluvial river is described, and a perturbation technique involving a small parameter representing the ratio of sediment transport to water transport is used to obtain the following results.
Abstract: A stability analysis of meandering and braiding perturbations in a model alluvial river is described. A perturbation technique, involving a small parameter representing the ratio of sediment transport to water transport, is used to obtain the following results.Under appropriate conditions, the existence of sediment transport and friction are necessary conditions for the occurrence of instability in the flow and on the bed; thus instability is not inherent in the flow alone. An Anderson-type scale relation for longitudinal instability is obtained for meandering. A relation estimating the number of braids and differentiating between meandering and braided regimes is derived. These relations are independent of sediment transport.
497 citations
"Analysis of turbulent flow characte..." refers background in this paper
...Turbulent phenomenon in braided rivers is much more complex than that in straight and meandering rivers, turbulent flow characteristics around the braid bar are not thoroughly researched till now (Ferguson 1993; Parker 1976)....
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TL;DR: In this paper, the effects of surface roughness on a turbulent boundary layer were investigated by comparing measurements over two rough walls with measurements from a smooth wall boundary layer, showing that the roughness effects are not confined to the wall region.
Abstract: The effects of surface roughness on a turbulent boundary layer are investigated by comparing measurements over two rough walls with measurements from a smooth wall boundary layer. The two rough surfaces have very different surface geometries although designed to produce the same roughness function, i.e. to have nominally the same effect on the mean velocity profile. Different turbulent transport characteristics are observed for the rough surfaces. Substantial effects on the stresses occur throughout the layer showing that the roughness effects are not confined to the wall region. The turbulent energy production and the turbulent diffusion are significantly different between the two rough surfaces, the diffusion having opposite sign in the region γ/δ < 0.5. Although velocity spectra exhibit differences between the three surfaces, the mean energy dissipation rate does not appear to be significantly affected by the roughness.
461 citations
TL;DR: In this paper, an evaluation of the effectiveness of the VITA, Quadrant, TPAV, U -level, Positive slope, and VITa with slope burst-detection algorithms has been done by making direct comparisons with flow visualization.
Abstract: An evaluation of the effectiveness of the VITA, Quadrant, TPAV, U -level, Positive slope, and VITA with slope burst-detection algorithms has been done by making direct comparisons with flow visualization. Measurements were made in a water channel using an X-type hot-film probe located in the near-wall region. Individual ejections from bursts which contacted the probe were identified using dye flow visualization. The effectiveness of each of the detection algorithms was found to be highly dependent on the operational parameters, i.e. threshold levels and averaging or window times. These parameters were adjusted so that the number of events detected by each of the algorithms corresponded to the number of ejections identified by flow visualization, while the probability of a false detection was minimized. Comparing the detection algorithm using these optimum parameter settings, the Quadrant technique was found to have the greatest reliability with a high probability of detecting the ejections and a low probability of false detections. Furthermore, it was found that the ejections detected by the Quadrant technique could be grouped into bursts by analysing the probability distribution of the time between ejections.
324 citations
"Analysis of turbulent flow characte..." refers methods in this paper
...Bogard and Tiederman (1986) had used seven different algorithms for detecting coherent structure in open channel flow....
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