An experimental study into local scour in a channel caused by a 90° bend

2006 ◽  
Vol 33 (7) ◽  
pp. 902-911 ◽  
Author(s):  
Jueyi Sui ◽  
Daxian Fang ◽  
Bryan W Karney
Keyword(s):  
Froude Number ◽  
Flow Direction ◽  
Local Scour ◽  
Scour Depth ◽  
Factors Affecting ◽  
Downstream Section ◽  
Series Of Experiments ◽  
Bed Material ◽  
Hydraulic Variables

Based on a series of experiments, this paper explores the influence of a 90° change in flow direction on local scouring. The influence on local scour patterns due to hydraulic parameters such as the Froude number, the slope of the protection wall, the width of the protection apron along the outside wall of the downstream section, and the grain size of the channel bed material is examined. Protection-wall slopes ranging from 1:0.5 to 1:4 (vertical to horizontal) were investigated, as were different widths of the protection apron; the goal was to ascertain the role of these variables in local scour patterns in the vicinity of the bend. The factors affecting local scour depth are related through empirical equations to key hydraulic variables, the slope of the protection wall, and the width of the protection apron.Key words: bent flume, channel erosion, Froude number, scour depth, slope of protection wall (SPW), width of protection apron (WPA).

scholarly journals Nose-Angle Bridge Piers as Alternative Countermeasures for Local Scour Reduction

2018 ◽  
Vol 13 (2) ◽  
pp. 110-120 ◽  
Author(s):  
Ibtesam Abudallah Habib ◽  
Wan Hanna Melini Wan Mohtar ◽  
Atef Elsaiad ◽  
Ahmed El-Shafie
Keyword(s):  
Froude Number ◽  
Local Scour ◽  
Bridge Piers ◽  
Scour Depth ◽  
Skew Angle ◽  
Flow Angle ◽  
Sediment Size ◽  
Low Froude Number ◽  
Skew Angles ◽  
Depth Reduction

This study investigates the performance nose-angle piers as countermeasures for local scour reduction around piers. Four nose angles were studied, i.e., 90°, 70°, 60° and 45° and tested in a laboratory. The sediment size was fixed at 0.39 mm whereas the flow angle of attack (or skew angle) was varied at four angles, i.e., skew angles, i.e., 0°, 10°, 20° and 30°. Scour reduction was clear when decreasing nose angles and reached maximum when the nose angle is 45°. Increasing the flow velocity and skew angle was subsequently increasing the scour profile, both in vertical and transversal directions. However, the efficiency of nose angle piers was only high at low Froude number less than 0.40 where higher Froude number gives minimal changes in the maximum scour depth reduction. At a higher skew angle, although showed promising maximum scour depth reduction, the increasing pier projected width resulted in the increase of transversal lengths.

scholarly journals Investigation of local scour around tandem piers for different skew-angles

2018 ◽  
Vol 40 ◽  
pp. 03008 ◽  
Author(s):  
Sargol Memar ◽  
Mohammad Zounemat-Kermani ◽  
Ali-Asghar Beheshti ◽  
Giovanni De Cesare ◽  
Anton J. Schleiss
Keyword(s):  
Flow Direction ◽  
Local Scour ◽  
Scour Depth ◽  
Skew Angle ◽  
Approach Velocity ◽  
Sheltering Effect ◽  
Skew Angles

In the present study the effect of the skew-angle of the alignment of tandem piers on local scour depth around them is investigated. The tandem piers were aligned with different skew-angles of θ=0°,30°,45°,60°,90° with respect to the flow direction. The results indicatethat with the increment of the skew-angle, the influence of sheltering effects is decreased. In other word, since the sheltering effect of the upstream pier is declined (which reduces the approach velocity for the downstream pier) the scour depth around downstream pier increases. The results show that the maximum scour depth occurs at both piers for the skew-angle of θ=45°.Furthermore, the best configuration to aligned tandem piers was achieved at the skew-angle of θ=30°.

scholarly journals Examination of Blockage Effects on the Progression of Local Scour around a Circular Cylinder

Water ◽  
2019 ◽  
Vol 11 (12) ◽  
pp. 2631 ◽  
Author(s):  
Priscilla Williams ◽  
Ram Balachandar ◽  
Tirupati Bolisetti
Keyword(s):  
Local Scour ◽  
Estimation Methods ◽  
Scour Depth ◽  
Blockage Ratio ◽  
Small Influence ◽  
Channel Blockage ◽  
Median Diameter ◽  
Equilibrium Scour Depth ◽  
Future Work

An evaluation of scour estimation methods has indicated that the effects of blockage ratio are neglected in both scour modelling and development of new predictive methods. The role of channel blockage on the mechanism and progression of local scour is not well understood, and further analysis is required in order to incorporate this effect into scour estimation. In the present investigation, local scour experiments were carried out under varying blockage ratio. The results were compared with data from literature in order to explore the effects of blockage ratio (D/b, where D is the pier diameter, and b is the channel width) on equilibrium scour depth (dse/D, where dse is the depth of scour at equilibrium). It was determined that D/b had a small influence on both dse/D and the progression of scour depth (ds/D) when relative coarseness D/d50 < 100 (where d50 is the median diameter of sediment), and that the influence appeared to be amplified when D/d50 > 100. The efficacy of scour estimation methods used to predict the progression of local scour was also dependent on D/d50. A method of scour estimation used to predict dse/D was evaluated, and it was similarly found to be particularly effective when D/d50 < 100. In future work, further experiments and analysis in the range of D/d50 > 100 are required in order to establish the role of D/b under prototype conditions and to refine existing scour estimation methods.

scholarly journals Investigation of Local Scour around L-Shape Submerged Groynes in Clearwater Conditions

2021 ◽  
Vol 28 (3) ◽  
pp. 159-169
Author(s):  
Saleh Issa Khassaf ◽  
Budoor Mohammed Rashak
Keyword(s):  
Froude Number ◽  
Local Scour ◽  
Scour Depth ◽  
Contour Lines ◽  
Low Profile ◽  
Scour Hole ◽  
Number Flow ◽  
Flow Intensity ◽  
Good Determination ◽  
New Formula

Submerged Groynes are low profile linear structures that are generally located on the outside bank to form Groynes fields and prevent the erosion of stream banks by redirecting high-velocity flow away from the bank. This research was studied in detail through two major stages. The first stage of the study is based on laboratory experiments to measure the development of local scour around L-shape submerged Groyne with the time, and special attention is given to the effects of different hydraulic and geometric parameters on local scour. Also; maps were drawn showing contour lines that represented the bed levels for maximum scour depth after reaching the equilibrium case. The result showed that a decrease in the scour depth ratio due to the increasing submerged ratio, and the number of Groynes. While the scour hole geometry will increase with the Froude number, flow intensity, and the spacing between Groynes, the decreasing percentage in the scour hole was measured to be about (4.3) % and (4.4) % for decreasing the spacing between Groynes from (2Lg) to (1.5Lg). Besides, it was range about (11.1) % and (14.0) % when reducing the spacing from (1.5Lg) to (Lg) under the same value of maximum Froude number. The second stage of the study is based on experimental results. A new formula was developed by using statistical analysis and it was found that a good determination coefficient.

scholarly journals Physical Modeling of Spatial and Temporal Development of Local Scour at the Downstream of Bed Protection for Low Froude Number

Water ◽  
2019 ◽  
Vol 11 (5) ◽  
pp. 1041 ◽  
Author(s):  
Sung Won Park ◽  
Jin Hwan Hwang ◽  
Jungkyu Ahn
Keyword(s):  
Equilibrium State ◽  
Froude Number ◽  
Fixed Bed ◽  
Local Scour ◽  
Dominant Factor ◽  
Scour Depth ◽  
Dimensionless Time ◽  
Temporal Development ◽  
Low Froude Number ◽  
Bed Protection

Local scour at the downstream of the river bed protection is one of the most important parameters for the design criteria and sustainable management of the hydraulic structures. Previously, various researches on its process in the equilibrium state have been suggested with experimental and numerical approaches. In this study, relatively long-term laboratory experiments of local scouring at the downstream of fixed bed in an open channel were conducted with mono-granular sediment bed and analyzed about maximum scour depth and its temporal development. In particular, we conducted experiments with relatively low Froude number (less than 0.5) and their duration of tests was exceeded over 700 hours. We modified the relationship between the dimensionless time and length scales of the maximum scour depth of the local scour hole based on the turbulent shear layer thickness. A new functional relationship between dominant factors and the maximum scour depth in the equilibrium state were suggested and compared with previously suggested formula. Also, from the results by nonlinear regression, Froude number was founded as a dominant factor on the prediction of equilibrium maximum scour depth.

Local scour around bridge abutments including effects of relative bed coarseness and blockage ratio

2016 ◽  
Vol 43 (1) ◽  
pp. 51-59
Author(s):  
Peng Wu ◽  
Ram Balachandar
Keyword(s):  
Strong Influence ◽  
Empirical Equation ◽  
Local Scour ◽  
Experimental Results ◽  
Scour Depth ◽  
Blockage Ratio ◽  
Flow Depth ◽  
Bridge Abutments ◽  
Additional Support

Based on laboratory scale experiments, the role of relative bed coarseness, approach flow depth, and blockage ratio on local scour around semi-circular bridge abutments are discussed. The results reveal that the approach flow depth and relative bed coarseness have a very strong influence on the scour geometry. With the increase of relative bed coarseness, the scour width and scour depth decrease correspondingly. Larger blockage ratios result in larger scour but the relative effects is the smallest compared to the approach flow depth and relative bed coarseness. An empirical equation is developed based on the experimental results. The study provides additional support for considering relative bed coarseness, flow depth, and blockage ratio in scour prediction formulae.

scholarly journals Experimental Study of Local Scour around Caissons under Unidirectional and Tidal Currents

Water ◽  
2020 ◽  
Vol 12 (3) ◽  
pp. 640 ◽  
Author(s):  
Qiqi Xiang ◽  
Kai Wei ◽  
Fang Qiu ◽  
Changrong Yao ◽  
Yadong Li
Keyword(s):  
Cross Sections ◽  
Tidal Current ◽  
Opposite Effect ◽  
Tidal Currents ◽  
Local Scour ◽  
Bridge Engineering ◽  
Scour Depth ◽  
Factors Affecting ◽  
Main Factors ◽  
The Difference

Local scour around caissons under currents has become one of the main factors affecting the safety of foundation construction and operation in coastal and offshore bridge engineering. Local scour occurs not only in the operation stage, when the caisson has settled into the sediment, but also in the construction stage, when the caisson is suspended in water. In this study, the local scour induced by unidirectional and tidal currents around settled caissons with different cross-sections (circular, square, and diamond) was experimentally investigated. Circular and square caissons were selected to investigate the difference in local scour of suspended caissons under unidirectional and tidal currents. The main findings from the experimental results were: (1) the temporal development of scour under tidal current was slower than that of unidirectional current; (2) the effect of current type can significantly influence the size and location of maximum scour depth around circular and square caissons; (3) the appropriate choice of cross-section could reduce the maximum scour depth around the settled caisson; (4) the maximum scour depth of tidal current was smaller than that of unidirectional current when the caisson was settled into the sediment, while the opposite effect occurred when the caisson was suspended in water.

Effect of grain size on local channel scour below a sluice gate

2001 ◽  
Vol 28 (3) ◽  
pp. 440-451 ◽  
Author(s):  
J A Kells ◽  
R Balachandar ◽  
K P Hagel
Keyword(s):  
Grain Size ◽  
Flow Rate ◽  
Image Data ◽  
Local Scour ◽  
Scour Depth ◽  
Sluice Gate ◽  
Time Period ◽  
Depth Video ◽  
Bed Material ◽  
Cohesive Bed

In this study, the effect of grain size on the dynamics of local scour processes is discussed in the context of the erosion that takes place downstream from a submerged sluice gate. Four gradations of non-cohesive bed material were used to study the scour process for various tailwater depth and flow rate conditions. The sand gradations included three sizes of uniformly graded sand and a fourth size, which was obtained by mixing the three uniform sands in equal proportions by weight. A total of 36 tests was carried out, each for a period of 24 h. An equilibrium scour condition was not attained over this time period for any of the tests, although a sense of similarity in the bed profiles is observed in the region close to the sluice gate. The present results indicate that the depth and the area of scour are highly dependent on the bed grain size, both increasing as the grain size is reduced. As well, it was found that the tests with a mixed (i.e., graded) sand bed resulted in less scour relative to those in which a uniformly graded sand of similar grain size was used. Moreover, the maximum scour depth increases with increases in the discharge and the tailwater depth. Finally, it was found that the location of the point of maximum scour depth, as measured from the upstream end of the erodible sand bed, moved downstream with an increase in either the discharge or tailwater depth and upstream with an increase in the grain size.Key words: grain size, grain size distribution, local scour, scour dynamics, sluice gate, tailwater depth, video image data acquisition.

scholarly journals Modeling Local Scour around a Cylindrical Pier with Circular Collar with Tilt Angles (Counterclockwise around the Direction of the Channel Cross-Section) in Clear-Water

Water ◽  
2021 ◽  
Vol 13 (22) ◽  
pp. 3281
Author(s):  
Hongliang Qi ◽  
Weiping Tian ◽  
Haochi Zhang
Keyword(s):  
Cross Section ◽  
Tilt Angle ◽  
Early Stage ◽  
Flow Direction ◽  
Local Scour ◽  
Channel Cross Section ◽  
Scour Depth ◽  
Clear Water ◽  
Eddy Simulation ◽  
Scouring Depth

This research explores how a circular collar with a tilt angle (counterclockwise around the direction of the channel cross-section) could affect the local scour depth around a single cylindrical pier in clear-water based on Large Eddy Simulation (LES) in six cases. The results show that a horizontal circular collar is the best for reducing the local scour depth. With the increases of the tilt angle, the effect on reducing the local scour depth decreases gradually and is even counterproductive at the scour equilibrium. At the early stage of scouring, cases with circular collars show obvious scouring depth reductions. The smaller the tilt angle is, the better and longer-lasting the protection that the circular collar can provide. When the tilt angle is smaller than 5°, the location of the maximum local scouring is around 90–115° (the angle is measured clockwise from the flow direction) on both sides of the pier. When the tilt angle is greater than 5°, the depth of local scouring in the range around −115° to 115° is close to the maximum local scouring depth. Significantly larger areas reach the maximum scouring depth when the tilt angle increases. Compared to Case 1 (the pier without a circular collar), in the cases with a circular collar, the topographies downwards the pier in 1.0D (D is the diameter of the bridge pier) are changed to siltation from scouring. The topography downwards the pier changes from scouring to siltation with the increase of the tilt angle, and the shape of siltation changes from a long-narrow rectangle to an equilateral triangle. This study may provide valuable insights into the protection of the local scour of the pier.

scholarly journals Experimental study of local scour around T-shaped spur dike in a meandering channel

2020 ◽  
Author(s):  
Ravi Prakash Tripathi ◽  
K. K. Pandey
Keyword(s):  
Froude Number ◽  
Research Work ◽  
Local Scour ◽  
Scour Depth ◽  
Spur Dike ◽  
Meandering Channel ◽  
Work Related ◽  
Channel Bend ◽  
River Training ◽  
Training Structure

Abstract A spur dike is mainly constructed as a river-training structure and is primarily used to prevent bank erosion. The restriction to flow caused by the construction of a spur dike promotes local scour around the structure. In the case of a dike placed in a channel bend, the scour becomes more aggressive. The literature review found that the research work related to local scour around a spur dike located in a meandering channel is very limited or minimal. Therefore, an experimental investigation was conducted to study the local scour process around a T-shaped spur dike placed at different locations along the outer bank (or concave) of a reverse-meandering channel. Non-dimensionalized empirical equations for temporal and maximum local scour depth were developed as the function of the Froude number of approach flow and spur dike location. It is observed that local scour around the dike increases with the increase in Froude number and location in the meander (measured from the entry to meander). The formulation for the maximum scour depth was further evaluated with the experimental data related to the 180° bend, from literature, and it was found that the proposed equation's application is very much limited.

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