Enhancing Utility of Submerged Vanes with Collar
24 Feb 2010-Journal of Hydraulic Engineering (American Society of Civil Engineers)-Vol. 136, Iss: 9, pp 651-655
TL;DR: In this article, the advantages of using collars in case of submerged vanes and providing insight into selection of appropriate collar shapes were discussed and a collar of circular shape was found more suitable for a rectangular vane.
Abstract: Submerged vanes are submerged foils of low height and larger length, constructed in a river at an angle of attack α to the flow to modify the near-bed flow pattern and redistribute flow and sediment transport within the channel cross section. At a Froude number (F) of 0.13, the local scour development around the submerged vane without a collar was not enough to dislodge the vane whereas at F=0.25, there was a significant local scour hole around the vane and the vane was dislodged. With the introduction of a collar at the leading edge of a submerged vane, the scour depth at the leading edge of the vane was reduced to zero. A collar of circular shape was found more suitable for a rectangular vane. Recommendations for sizing collars at two values of F are given. The optimal α for a rectangular vane with a collar was found close to 40°. The study clearly indicates the advantages of using collars in case of submerged vanes and provides insight into selection of appropriate collar shapes.
Citations
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TL;DR: In this paper, a series of experiments were conducted in a 180° bend laboratory channel to study flow erosion and effective ness of the submerged vane in reducing scour depth.
Abstract: Unsteadiness of the vertical velocity profile and secondary flow in open channel bends poses serious problems in hydraulic engineering design. Insertion of vertical submerged vanes in the channel bend at an optimum angle with the tangential component of flow can minimize the unsteadiness and generation of secondary flow resulting in the reduction of scour depth at the outer bank. A series of experiments were conducted in a 180° bend laboratory channel to study flow erosion and effective ness of the submerged vane in reducing scour depth. The average approach to flow velocity at 0.20 m flow depth above the lowest initial bed level was 25 cm/s. An Acoustic Doppler Velocimeter (ADV) was used to measure the three-dimensional time-averaged velocity components at different azimuthal sections on stabilized nonscoured beds without vane. Scour bed profile without vanes shows that bank erosion in a 180° parabolic-shaped bed channel occurs mostly at the zone from bend angles 120° to 140°. Vanes were installed at angles of 10°, 15°, 20°, 30°, and 40° to the tangential flow component maintaining a spacingof 75 cm distance from one vane to another. Experimental results show that a 15° vane angle produces best result in reducing outer bank scour in a parabolic-shaped channel. The data presented in this paper can also be used for validating three-dimensional turbulence models for simulating flows in a curved channel.
20 citations
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TL;DR: In this article, the authors review and validate the findings of Odgaard and his associates by utilizing computational fluid dynamics and experiments as a tool in which the vane generated vorticity in the downstream was maximized in order to obtain optimum vane parameters for single and multiple vane arrays.
Abstract: Submerged vanes are airfoils which are in general placed at certain angle with respect to the flow direction in a channel to induce artificial circulations downstream. By virtue of these artificially generated circulations, submerged vanes were utilized to protect banks of rivers against erosion, to control shifting of rivers, to avoid blocking of lateral intake with sediment deposition, etc. Odgaard and his associates have experimentally obtained the optimum vane sizes and recommended that it can be used for vane design. This paper is an attempt to review and validate the findings of Odgaard and his associates by utilizing computational fluid dynamics and experiments as a tool in which the vane generated vorticity in the downstream was maximized in order to obtain optimum vane parameters for single and multiple vane arrays.
14 citations
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TL;DR: In this paper, the effects of various parameters such as the Froude number (Fr), angle of submerged vanes to the flow, angle of vanes location in the bend, distance between vanes, height and length of the vanes on the dimensionless volume of the scour hole were experimentally studied.
Abstract: Submerged vanes are installed on rivers and channel beds to protect the outer bank bends from scouring. Also, local scouring occurs around the submerged vanes over time, and identifying the effective factors on the scouring phenomena around these submerged vanes is one of the important issues in river engineering. The most important aim of this study is investigation of scour pattern around submerged vanes located in 180° bend experimentally and numerically. Firstly, the effects of various parameters such as the Froude number (Fr), angle of submerged vanes to the flow (α), angle of submerged vane location in the bend (θ), distance between submerged vanes (d), height (H), and length (L) of the vanes on the dimensionless volume of the scour hole were experimentally studied. The submerged vanes were installed on a 180° bend whose central radius and channel width were 2.8 and 0.6 m, respectively. By reducing the Froude number, the scour hole volume decreased. For all Froude numbers, the biggest scour hole formed at θ = 15°. In all models, by increasing the Froude number, the scour hole volume significantly increases. In addition, by increasing the submerged vanes’ length and height, the scour hole dimensions also grow. Secondly, using gene expression programming (GEP), a relationship for determining the scour hole volume around the submerged vanes was provided. For this model, the determination coefficients (R2) for the training and test modes were computed as 0.91 and 0.9, respectively. In addition, this study performed partial derivative sensitivity analysis (PDSA). According to the results, the PDSA was calculated as positive for all input variables.
12 citations
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TL;DR: In this paper, the optimal spatial distribution of submerged vanes is determined by estimating the interaction between a row of vanes and the banks of the channel, and the best results were obtained when the spacing between vanes in a row increased gradually outward from the target bank at an average ratio of approximately 1.2.
Abstract: This study developed a methodology by which to determine the optimal spatial distribution of submerged vanes positioned across a river channel to protect the stream bank from erosion. The methodology is based on an improved model for estimating the interaction between a row of vanes and the banks of the channel. The results show that the optimal spatial distribution of vanes is related primarily to the radius of the channel curve and the width of the channel. The sediment Froude number and angle of flow to the vanes were shown to have far less effect. The best results were obtained when the spacing between vanes in a row increased gradually outward from the target bank at an average ratio of approximately 1.2. This provides a handy guideline for the preliminary layout of vane arrays.
12 citations
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TL;DR: In this paper, the curvature of the pier cross section was evaluated with computational fluid dynamics (CFD) simulations to evaluate the effect of streamlining on the flow field and selected the cross section that resulted in the smallest value of the maximum bed shear stress as the optimal cross section for the subsequent three-dimensional (3D) study.
Abstract: Bridge scour is one of the most critical causes of bridge failure. Existing scour countermeasures either passively prevent the development of scour holes by stabilizing the critical shear zone or actively reduce the turbulence intensity in the vicinity of the pier surface. This paper proposes streamlining of the bridge pier as an option to reduce turbulence intensity actively in the local zone and thus decrease overall local scour potential. The effect of the curvature of the pier cross section was evaluated with computational fluid dynamics (CFD) simulations. To reduce computational cost, two-dimensional CFD simulations were conducted to model the flow fields around test cases having different pier cross sections. Simulation results were systematically analyzed and compared to evaluate the effect of streamlining on the flow field. The cross section that resulted in the smallest value of the maximum bed shear stress was selected as the optimal cross section for the subsequent three-dimensional (3-D) study...
9 citations
References
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TL;DR: In this article, the effect of using a slot in the pier, or a collar around it, as devices for controlling the depth of scour was examined in clear-water conditions, and it was shown that the use of a slot alone (with a width equal to one-fourth of the pier diameter) can reduce equilibrium scour depth by as much as 20%.
Abstract: The objective of this study is to review existing methods and propose alternative or additional devices for scour protection around bridge piers. Engineering methods used in dealing with pier‐scour problems include placing coarse riprap around the foundations. An inverted filter layer is normally placed beneath the riprap to overcome leaching problems. Practical difficulties in laying the filter according to specifications, especially in deep water, often cause failure of the riprap layer. The study examines the effect of using a slot in the pier, or a collar around it, as devices for controlling the depth of scour. Experiments conducted in clear‐water conditions show that the use of a slot alone (with a width equal to one‐fourth of the pier diameter) can reduce equilibrium scour depth by as much as 20%. A combination of slot and collar can further reduce the scour depth. These devices may be useful as additional or alternative devices for scour protection.
179 citations
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TL;DR: In this paper, the use of pier slots and collars for reducing local scour at bridge piers was examined through experiments and the efficacy of slots, of different lengths and at different angles of attack, was studied through experiments.
Abstract: The present study examines the use of pier slots and collars for reducing local scour at bridge piers. The efficacy of slots, of different lengths and at different angles of attack, was studied through experiments. The reduction of scour due to the placement of circular collars, of different sizes and at different elevations, was also investigated. Analysis of the data from the experiments as well as data from earlier studies led to an equation for the maximum scour depth around circular bridge piers fitted with collars. The equation applies to local scour of uniform-sized sediment in clear-water flow.
157 citations
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TL;DR: In this article, it was shown that short, vertical, submerged vanes installed at incidence to the channel axis in the outer half of a river-bend channel significantly reduce the secondary currents and the attendant undermining and high-velocity attack of the outer bank.
Abstract: It is shown, theoretically and by a physical model, that short, vertical, submerged vanes installed at incidence to the channel axis in the outer half of a river-bend channel significantly reduce the secondary currents and the attendant undermining and high-velocity attack of the outer bank. The effect of the vanes on the secondary flow is estimated by a simple torque calculation using the Kutta-Joukowski theorem. A design relation for the vane spacing is derived by equating the torque, about the channel centroid, produced by the flow curvature to that resulting from the lateral force exerted on the vanes. The relation is verified in an idealized, physical model of a bend of the Sacramento River, California.
121 citations
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TL;DR: The theory of submerged vanes described in the companion paper is tested with laboratory and field data as mentioned in this paper, and they suggest that the vane technique is a viable alternative to traditional techniques.
Abstract: The theory of submerged vanes described in the companion paper is tested with laboratory and field data. The laboratory data are from experiments in curved, and straight, recirculating sediment flumes. The field data are from river bends in which, prior to installation of vanes, the banks were eroding, and from a straightened bridge waterway in which sediment deposits were causing a change of channel alignment, bank erosion, and undermining of the bridge abutment. All data support the theory, and they suggest that the vane technique is a viable alternative to traditional techniques. The design procedure is described and illustrated with numerical examples, and vane material and typical vane layouts are discussed. Layouts are presented for protection of stream banks against erosion and for amelioration of shoaling problems in navigation channels, at water intakes, in bridge crossings, at river confluences, and at diversions.
92 citations
Journal Article•
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TL;DR: Submerged vanes as discussed by the authors are small river training structures used for protection of streambanks against erosion and for amelioration of shoaling problems in navigation channels, at water intakes, in bridge crossings, and at diversions.
Abstract: Submerged vanes are small river training structures used for protection of streambanks against erosion and for amelioration of shoaling problems in navigation channels, at water intakes, in bridge crossings, and at diversions. The structures function by modifying the near-bed flow pattern and redistributing flow and sediment transport within the channel cross section. The theory of the structures is developed elsewhere. The paper describes the design guidelines and typical applications.
87 citations