HYDRAULIC STRUCTURE FAIRING WITH VORTEX GENERATOR

Abstract

Discussed are several practical cost-effective refinements, extensions, additions, and improvements to the manufactured three-dimensional convex-concave fairing with attached vortex generators that was disclosed by Simpson et al. (U.S. Pat. No. 8,348,553). Extensions are disclosed for bridge piers and abutments at larger angles of attack of up to 45°, for piers and abutments downstream of a bend in a river where there is large-scale swirling approach flow, and for piers in close proximity to an adjacent pier of abutment.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Ser. No. 61/888,162, filed Oct. 8, 2013. The invention generally relates to the fields of Civil Engineering, Hydraulic Engineering, and Soil and Water Conservation. More specifically, the invention relates to a manufactured device to prevent scour around hydraulic structures.

BACKGROUND OF THE INVENTION

Removal of river bed substrate around bridge pier and abutment footings, also known as scour, presents a significant cost and risk in the maintenance of many bridges throughout the world. Bridge scour at the foundations of bridge piers and abutments is one of the most common causes of highway bridge failures. It has been estimated that 60% of all bridge failures result from scour and other hydraulic-related causes (Briaud, 2006). In 1973, a study by the US Federal Highway Administration (FHWA) was conducted to investigate 383 bridge failures caused by catastrophic floods, and it concluded that 25 percent involved pier damage and 72 percent involved abutment damage (Richardson et al., 1993). This has motivated research on the causes of scour at bridge piers and abutments (Ettema et al., 2004) and led bridge engineers to develop numerous countermeasures that attempt to reduce the risk of catastrophe. Unfortunately, all such countermeasures currently in existence and practice are temporary responses that cannot endure throughout the lifetime of the bridge and do not prevent the formation of scouring vortices, which is the root cause of the local scour. Consequently, sediment such as sand and rocks from around the foundations of bridge abutments and piers is loosened and carried away by the flow during floods, which may compromise the integrity of the structure. When these temporary scour countermeasures are used for at-risk bridges, expensive monitoring technologies and support professionals are required to enable sufficient time for implementing contingency plans when failure is likely. Even designing bridge piers or abutments with the expectation of some scour is highly uncertain, since a study (Sheppard et al., 2011) showed huge uncertainties in scour data from hundreds of experiments. Other than the innovation of Simpson et al. (U.S. Pat. No. 8,348,553), none of the conservative current bridge pier and abutment footing or foundation designs prevents scouring vortices, so the probability of scour during high water or floods is present in all of those designs.

The bridge foundations in a water current (WC), such as piers (P) and abutments (A), change the local hydraulics drastically because of the generation of large-scale unsteadiness and shedding of coherent vortices, such as horseshoe vortices, by the piers and abutments. FIG. 1 is a sketch of the horseshoe vortex (HV) formed around the base of a bridge pier (P) hydraulic structure by a separating boundary layer. The horseshoe vortex (HV) has high lift and shear stress and triggers the onset of sediment scour and a scour hole (SH) is formed as shown in FIG. 1.

The flow field around a vertical-wall abutment (A) is highly three-dimensional and involves strong separated vortex flow around the abutment as shown in FIG. 2. A separation bubble (SB) is formed at the upstream corner of the abutment. Unsteady shed wake vortices (WV) are created due to the separation of the flow at the abutment corners. These wake vortices (WV) are very unsteady, are oriented approximately vertical and have low pressure at the vortex cores. These vortices act like small tornadoes, lifting up sediment from the sediment bed (SB) and creating a large scour hole (SH) behind the abutment (A) and a downstream scour hole (DSH). The down flow (DF) at the front of the abutment is produced by the large vertical stagnation pressure gradient of the approaching flow. The down flow rolls up and forms the primary vortex (PV) as shown in FIG. 2, which is similar to the formation of the horseshoe vortex around a single bridge pier. FIGS. 3 and 4 show the flowfield (FF) past a wing-wall abutment (A) and spill-through abutment (A), respectively, where deep contraction scour can occur due to vortices, high turbulence (HT), and flow separation zones (FS). Bridge scour is comprised of three components: long-term aggradations and degradation of the river bed, general scour at the bridge, and local scour at the piers or abutments (Lagasse et al. 2001). The structural countermeasures are used primarily to minimize local scour such as extended footings, scour collars, pier shape modifications, debris deflectors, and sacrificial piles, all of which are only marginally effective. A number of collar devices (Titman, U.S. Pat. No. 3,529,427; de Werk, U.S. Pat. No. 4,279,545; Larsen, U.S. Pat. No. 3,830,066; Larsen, U.S. Pat. No. 3,844,123; and Pedersen, U.S. Pat. No. 3,859,803) encircle the lower end of hydraulic structures, but do not prevent scour on the downstream side of the structure. A similar anti-scour apparatus comprising an upper and a lower collar was patented by Loer (U.S. Pat. No. 4,717,286). U.S. Pat. No. 4,114,394 by Larsen describes the use of a sheet or sack housing film material, which is secured around a hydraulic structure with cables. All of the above collar devices would only have a local effect and local scour will still happen around the vicinity of the collar, as shown by Tian et al. (2010) in work performed in the AUR flume. In U.S. Pat. No. 5,839,853 (Oppenheimer and Saunders), one structure of vortex generators, located upstream of the hydraulic structure, is specified to produce a pair of stream-wise vortices that move toward the free surface and protect the hydraulic structure from the impact of oncoming debris. Another structure of vortex generators is positioned directly in front of the hydraulic structure to prevent the streambed from scouring by counteracting the horseshoe vortex (also sometimes called the necklace vortex) formed by separation at the hydraulic structure nose if there was no control. Simpson (2001) showed that this counteracting mechanism fails as a scour countermeasure.

For abutments, Barkdoll et al. (2007) reviewed the selection and design of existing bridge abutment countermeasures for older bridges, such as parallel walls, spur dikes located locally to the abutment, and horizontal collar-type plates attached to the abutment. Two similar collar devices (Lee et al., U.S. patent Ser. No. 10/493,100; Mountain, U.S. patent Ser. No. 11/664,991) are comprised of a number of interlocking blocks or bags in a monolayer or multilayer on the stream bed around abutments. However, these horizontal collar type scour countermeasures are only marginally effective as shown in the flume test results of Tian et al. (2010). The scour hole at the upstream abutment corner is eliminated, but the downstream scour hole due to the wake vortex shedding becomes more severe. In another approach to prevent streambed scour of a moving body of water, a scour platform is constructed by placing an excavation adjacent to the body of water (Barrett & Ruckman, U.S. Pat. No. 6,890,127). The excavation is covered with stabilizing sheet material, filled with aggregate, and extends up or downstream a desired length. However, the local scour around the excavation is inevitable, especially when the excavation is exposed to a moving body of water.

With the above prior art, Simpson et al. (U.S. Pat. No. 8,348,553, 19 claims) proved through model-scale and full-scale tests and disclosed a manufactured three-dimensional convex-concave fairing with attached vortex generators, for hydraulic structures such as bridge piers and abutments, whose shape prevents the local scour problem around such hydraulic structures even when the inflow is at an angle of attack to the hydraulic structure (FIGS. 5 and 6). The streamlined control Against Underwater Rampage (scAUR™, pronounced like ‘scour’) device is effective at preventing vortices that cause substrate transport for a large range of river flow conditions and bed substrate materials because it fundamentally alters the way the river flows around the pier.

FIG. 5 shows flow around a scAUR™ streamlined bridge pier fairing that remains attached without the formation of vortices. The convex-concave pier fairing nose (CCPFN) is located below the faired pier nose (FPN) and prevents the formation of vortices, as does the faired side (FS). The vortex generators (VG) cause the near wall flow to be energized before it moves over the downstream convex-concave fairing (DCCF) that is below the faired downstream stern (FDS).

FIG. 6 shows a retrofit to an abutment example with a faired abutment nose (FAN), a faired convex-concave abutment nose (FCCN), a faired abutment side (FS), vortex generators (VG), a downstream convex-concave fairing, using interlocking key (IK) sections. That device is a conventionally made concrete or fiber-reinforced composite, or combination of both, vortex generator equipped hydrodynamic fairing that is fit or cast over an existing or new hydraulic structure around the base of the structure and above the footing. The VorGAUR™ (Simpson et al., U.S. Pat. No. 8,434,723) vortex generators (VG) are positioned so as to energize decelerating near-wall flow with higher-momentum outer layer flow. The result is a more steady compact separation and wake and substantially mitigated scour inducing wake vortical (WV) flow as shown by a computational fluid dynamics (CFD) simulation (FIG. 7).

SUMMARY OF THE INVENTION

Discussed are several practical refinements, extensions, additions, and improvements to the manufactured three-dimensional continuous convex-concave fairing (scAUR™) with attached vortex generators that was disclosed by Simpson et al. (U.S. Pat. No. 8,348,553). The benefits to bridge owners and managers include actual scAUR™ manufacturing cost reductions as well as cost reductions by reducing the frequency and complexity of monitoring practices for scAUR™-fitted bridges and elimination of temporary fixes that require costly annual or periodic engineering studies and construction to mitigate scour on at-risk bridges. The probability of bridge failure and its associated liability to the public is totally avoided since the root cause of local scour is prevented. In an extension to Simpson et al. (U.S. Pat. No. 8,348,553), in addition to the concrete or fiber-reinforced composite, or combination thereof, hydrodynamic fairing disclosed in that patent, the present invention in practice is a cast-in-place, pre-cast, or sprayed (“shotcrete”) concrete, metal, or composite, or combinations thereof, hydrodynamic fairing that is fit or cast over one or more existing or new hydraulic structures around the base of these structures and above and around their footings. Molds for the concrete or composite fairing are made from wood and other natural materials, metal or composite materials, or combinations thereof. Such a properly designed fairing, as described by Simpson et al. (U.S. Pat. No. 8,348,553), prevents scouring vortex formation for both steady and unsteady flows, including oscillatory tidal flows. The vortex generators are constructed of cast-in-place, pre-cast, or sprayed (“shotcrete”) concrete, metal, or composite, or combinations thereof. The product is manufactured using existing metal, concrete, and composite materials technologies well known to professionals. As such, the product can be produced at minimal cost and with high probability of endurance over a long future period.

While the shape of the scAUR™ for bridge piers and abutments is fully three-dimensional, as described in detail by Simpson et al. (U.S. Pat. No. 8,348,553), it can be approximated by piece-wise continuous concave-convex-curvature surfaces within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces. No scouring vortices are produced in either case, but the piece-wise continuous curvature version can be manufactured at a much lower cost.

Discussed are applications to more types of abutments than shown by experiments by Simpson et al. (U.S. Pat. No. 8,348,553). In addition to the square-cornered abutments discussed in that patent, tests prove that the scAUR™ fairing with the help of specially designed VorGAUR™ vortex generators prevent scouring vortices for wing-wall and spill-through abutments.

In general, as described by Simpson et al. (U.S. Pat. No. 8,348,553), a single fully three-dimensional shape-optimized scAUR™ fairing with the help of specially designed VorGAUR™ (U.S. Pat. No. 8,434,723) vortex generators will prevent scour for a range of angles between the on-coming river flow and the pier centerline from −20° to +20°, with 0 angle defined when the flow is aligned with the pier centerline axis or side of an abutment. Here an extension is disclosed for bridge piers and abutments at larger angles of attack of up to 45°. Nose and tail sections on a pier form a dogleg shape and VorGAUR™ vortex generators prevent separations.

Here another extension is disclosed for bridge piers and abutments downstream of a bend in a river where there is large-scale swirling approach flow produced by the river bend. The fully three-dimensional shape is modified to meet the requirement of the design that the stream-wise gradient of surface vorticity flux must not exceed the vorticity diffusion rate in the boundary layer, thus preventing the formation of a discrete vortex. Another requirement is that a minimal size of the fairing be used that meets the first requirement.

When a pier is in close proximity to an adjacent pier or abutment, the flow between the two hydraulic structures is at a higher speed than if they were further apart. This means that at the downstream region of the pier or abutment there will be a greater positive or adverse stream-wise pressure gradient, which will lead to more and stronger flow separation and scouring vortices. To reduce this separation and possibilities for scour, a more gradual fairing or tail can be used.

As stated by Simpson et al. (U.S. Pat. No. 8,348,553), one can generalize the use of the vortex generators for various cases and applications. First, the vortex generators, such as the low drag asymmetric vortex generator (VorGAUR™) (Simpson et al., U.S. Pat. No. 8,434,723), should be located on the sides of the fairing well upstream of any adverse or positive pressure gradients and only in flow regions where there are zero pressure gradients or favorable or negative pressure gradients that will persist downstream of the vortex generator for at least one vortex generator length. This results in a well-formed vortex without flow reversal that can energize the downstream flow and prevent separation of the downstream part of the fairing. Secondly, the vortex generator should be at a modest angle of attack angle of the order of 10 to 20 degrees. Multiple vortex generators may be used on the sides of the fairing, as shown in FIGS. 5 and 6. The height and maximum width of the vortex generators need not be greater than the thickness of the approaching turbulent boundary layer upstream of the location of the vortex generators. The spacing between the vortex generators up the side of the fairing should be at least twice the maximum width of the vortex generator or twice the length of the vortex generator times the sine of the angle of attack, whichever is larger.

Aspects of the scAUR™ and VorGAUR™ design features have been expanded for use around the foundation in order to further protect the foundation from the effects of contraction scour, long term degradation scour, settlement and differential settlement of footers, undermining of the concrete scAUR™ segments, and effects of variable surrounding bed levels. Scour of the river bed away from the scAUR™ protected pier or abutment (open-bed scour) will occur first and the river bed level will be lower away from the pier or abutment. If the front of the foundation of a pier or abutment is exposed to approach flows, then a foundation horseshoe or scouring vortex is formed at the front which will cause local scour around the pier or abutment.

In another improvement disclosed here, a curved ramp in front of the foundation of a scAUR™ protected pier prevents the formation of this foundation horseshoe vortex and scour around an exposed foundation. A further innovation uses a vortex generator in front of each leading edge corner of the ramp, which will create a vortex that brings available loose open-bed scour materials toward the pier or abutment foundation to protect the pier or abutment. A third innovation uses vortex generators mounted on the sides of the foundation to bring more available loose open-bed scour materials toward the pier or abutment foundation to protect further the pier or abutment.

The innovative scour prevention devices in this present invention belong to the structural countermeasure category. Unlike the conventional and prior-art before Simpson et al. (U.S. Pat. No. 8,348,553) structural countermeasures, these scour countermeasure devices are invented based on a deep understanding of the scour mechanisms of the flow and consideration of structural and hydraulic aspects (Simpson 2001). A hydraulically optimum pier fairing constructed from any permanent solid material, whether for a straight-ahead, swirling, or curved inflow, prevents the formation of highly coherent vortices around the bridge pier or abutment and reduces 3D separation downstream of the bridge pier or abutment with the help of vortex generators, curved leading edge foundation ramp, and tail section.

In addition, these results show that the smooth flow over the pier or abutment produces lower drag force or flow resistance and lower flow blockage because low velocity swirling high blockage vortices are absent. As a result, water moves around a pier or abutment faster above the river bed, producing a lower water level at the bridge and lower over-topping frequencies on bridges during flood conditions for any water level, inflow turbulence level, or inflow swirling flow level. While tested both at model and full scale, there is no place for debris to get caught or no debris build up in front or around a pier or abutment with the scAUR™ and VorGAUR™ products. In cases where river or estuary boat or barge traffic occurs, the scAUR™ fairing can be constructed to withstand impact loads and protect piers and abutments.

The AUR scAUR™ product design concept with the herein refinements and extensions addresses the FHWA's Plan of Action on scour countermeasures (Hydraulic Engineering Circular No. 23, commonly ‘HEC-23’), such as avoiding adverse flow patterns, streamlining bridge elements, designing bridge pier foundations to resist scour without relying on the use of riprap or other countermeasures, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing and photograph executed in color. Copies of this patent or patent application publication with color drawing (s) and photograph (s) will be provide by the Office upon request and payment of the necessary fee.

FIGS. 1 though 4 (labeled “prior art”) show bridge piers and abutments with no prevention of scouring vortices.

FIG. 5 shows the prior-art of the Simpson et al. (U.S. Pat. No. 8,348,553) anti-scour optimized three-dimensional vortex-preventing streamlined continuous surface scAUR™ fairing at the bottom of a bridge pier with calculated flow streamline patterns.

FIG. 6 shows prior-art of the Simpson et al. (U.S. Pat. No. 8,348,553) anti-scour optimized vortex-preventing continuous surface scAUR™ fairing and its components for a vortex preventing design for the bottom of a bridge abutment.

FIG. 7 shows the prior-art wall flow pattern from CFD simulation at the downstream end of the continuous surface scAUR™ fairing for the approach flow aligned with the pier centerline or the straight-ahead case.

FIG. 8 shows surface oilflow results for the scAUR™ modified wing-wall abutment model with VGs. Flow is from right to left. The upward streaks show that the scAUR™ and VorGAUR™ products cause the flow to move up the wing-wall abutment. The gray region is produced by a mixture of the oilflow material and waterborne substances at the free surface.

FIG. 9 illustrates the bed level change contours after and before a flow around the wing-wall abutment model with length L into the flow without scAUR™ and VorGAUR™ products.

FIG. 10 shows the bed level change contours after and before flow around the scAUR™ modified wing-wall model (length L=159 mm) with VorGAUR™ VGs with no scour observed at any location.

FIG. 11 shows surface oilflow results for scAUR™ and VorGAUR™ modified sharp-leading edge (SLE) spill-through abutment model with 8 upstream VGs; the flow to moves up the abutment as it moves downstream, bringing low speed fluid from the bottom of the river and preventing scour; the gray region is produced by a mixture of the oilflow material and waterborne substances at the free surface. FIG. 12 illustrates bed level change contours after and before flow around the untreated spill-through abutment model (L=159 mm); note the dark blue scour hole.

FIG. 13 shows bed level change contours after and before flow around the scAUR™ modified sharp edge spill-through model with VorGAUR™ VGs (L=229 mm).

FIG. 14 is a top view of the scAUR 45 deg dogleg configuration.

FIG. 15a is an upstream view showing location of VGs on AUR pier model front right and rear left sides used in 45 degree high angle-of-attack AUR flume tests.

FIG. 15b is a downstream view of AUR model used in 45 degree high angle-of-attack AUR flume tests with a laser sheet showing no scour downstream of the model.

FIG. 16 shows the flow downstream of a 90 degree river bend from computational fluid dynamics (CFD); near-wall streamlines start at X/D=−4 and Y/D=0.13.

FIG. 17 is a top view of flow downstream of a 90 degree river bend from computational fluid dynamics (CFD); near-wall streamlines start at X/D=−4 and Y/D=0.13.

FIG. 18 shows a cross-section of the swirling secondary flow from CFD downstream of a 90 degree bend at X/D=−0.30, but upstream of pier; river surface flow at top of figure moves toward outer river bank on right; near-wall flow moves toward inner river bank on left.

FIG. 19 shows the gravel level after model flume test for H=12.7 mm high elevation (H/D=1/6) without a leading edge ramp and a scour hole at corner of foundation due to horseshoe vortex around foundation; note laser sheet for gravel surface measurement.

FIG. 20 shows the gravel level after flume test for H=12.7 mm high elevation (H/D=1/6) with a 19 mm high straight-sided curved leading edge ramp buried 6.4 mm in the gravel; note no scour around foundation.

FIG. 21 illustrates that a VorGAUR™ vortex generator at left upstream tramp corner creates CCW vortex that brings open-bed scour gravel toward the foundation.

FIG. 22 shows an example of a pier in close proximity to adjacent piers or abutments with scour at the downstream of the scAUR™ fairing with VorGAUR™ VGs model without a tail; laser light sheet shows scour hole downstream of pier on both sides of centerline and scour mound along the centerline.

FIG. 23 shows much lower scour around scAUR™ fairing with VorGAUR™ VGs model with the tail for the same flume run time as in FIG. 22.

FIG. 24 is a drawing of a full-scale sheet metal scAUR™ retrofit with VorGAUR™ for a pier with piece-wise continuous concave-convex curvature surfaces (1), (2) and (4) within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces; leading edge ramp (7) and pier foundation protecting VGs (3B and 3C) protect the foundation from open-bed scour.

FIG. 25 illustrates an example stainless steel piece-wise continuous surface retrofit scAUR™ fairing with VorGAUR™ (black) for a pier; VorGAUR™ vortex generators create vortices that bring low-speed flow up to prevent scour.

FIG. 26 is a drawing of full-scale sheet metal scAUR™ retrofit fairing with VorGAUR™ for a wing-wall abutment with piece-wise continuous concave-convex curvature surfaces 1, 2 and 4 within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces; vortex generators 3A reduce the flow separation and free-surface vortex effects while VGs 3B and 3C protect the foundation from open-bed scour.

FIG. 27 shows an example stainless steel piece-wise continuous surface scAUR™ retrofit fairing with VorGAUR™ for a wing-wall abutment.

FIG. 28 is a drawing of full-scale sheet metal retrofit scAUR™ with VorGAUR™ vortex generators for a spill-through abutment with piece-wise continuous concave-convex curvature surfaces 1, 2 and 4 within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces; vortex generators 3A reduce the flow separation and free-surface vortex effects while VGs 3B and 3C protect the foundation from open-bed scour.

FIG. 29 is a drawing of sheet metal scAUR™ with VorGAUR™ retrofit dogleg pier fairing with vortex generators; piece-wise continuous concave-convex curvature surfaces 1, 2, 4, and 10 are within definable tolerances to produce the same effects as continuous concave-convex-curvature surfaces; vortex generators 3A reduce the flow separation and free-surface vortex effects while VGs 3B and 3C protect the foundation from open-bed scour.

FIG. 30 is a drawing of full-scale sheet metal retrofit scAUR™ with VorGAUR™ vortex generators for a pier with a piece-wise continuous tail or stern; piece-wise continuous concave-convex curvature surfaces 1, 2 and 4 are within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces; vortex generators 3A reduce the flow separation and free-surface vortex effects while VGs 3B and 3C protect the foundation from open-bed scour.

FIG. 31 is a perspective top view drawing of concrete forms for the scAUR™ piece-wise continuous fairing during construction of a new pier: 11 for the nose, 12 for the sides, and 13 for the stern.

FIG. 32 shows an example of steel forms 11 and 12 for the scAUR™ piece-wise continuous fairing for construction of a new concrete pier 6.

FIG. 33 is a perspective view drawing of concrete forms for the scAUR™ piece-wise continuous fairing during construction of a new wing-wall abutment: 11 for the nose, 12 for the sides, 13 for the stern, and 14 for the corner fairing.

FIG. 34 shows an example of steel concrete forms 11, 12, and 14 for the scAUR™ piece-wise continuous fairing for construction of a new wing-wall abutment 6.

FIG. 35 is a drawing of a finished new construction wing-wall abutment 6 with scAUR™ piece-wise continuous concrete fairings 1, 2, 4, and 5 and VorGAUR™ vortex generators 3A for flow separation and surface vortex control and 3B and 3C for foundation protection from open-bed scour.

FIG. 36 is a perspective view drawing of steel concrete forms for the scAUR™ piece-wise continuous fairing during construction of a new spill-through abutment 6: 11 for the nose, 12 for the sides, 13 for the stern, and 14 for the corner fairing.

FIG. 37 shows an example of steel concrete forms 11, 12, and 14 for the scAUR™ piece-wise continuous fairing for construction of a new spill-through abutment 6; vorGAUR™ vortex generators 3A are shown mounted on the abutment for flow separation and surface vortex control.

FIG. 38 is a drawing of a finished new construction spill-through abutment 6 with scAUR™ piece-wise continuous concrete fairings 1, 2, 4, and 5 and VorGAUR™ vortex generators 3A for flow separation and surface vortex control and 3B and 3C for foundation protection from open-bed scour.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION; INVENTION OPERATION AND TEST RESULTS

Since bridge piers and abutments are the most common hydraulic substructures, in the following description bridge piers and abutments are used as examples for proof of concept; the local vortex preventing scour countermeasure technique described here can be extended to other hydraulic substructures. The components include:

• • 1. Piece-wise continuous three-dimensional convex-concave pier or abutment hydraulic structure nose fairing
  • 2. Piece-wise continuous curved side fairing for piers or abutments
  • 3. Specially designed vortex generators
  • 4. Piece-wise continuous three-dimensional convex-concave pier or abutment hydraulic structure downstream fairing
  • 5. Faired elliptical pier or abutment nose
  • 6. Existing or new bridge pier or abutment
  • 7. Piece-wise continuous curved pier foundation leading edge ramp
  • 8. Faired elliptical pier downstream surface
  • 9. Existing or faired circular pier nose or tail
  • 10. Piece-wise continuous curved pier nose or tail extension
  • 11. Mold for piece-wise continuous three-dimensional convex-concave pier or abutment hydraulic structure nose fairing
  • 12. Mold for piece-wise continuous curved side fairing for piers or abutments
  • 13. Mold for piece-wise continuous three-dimensional convex-concave pier or abutment hydraulic structure downstream fairing
  • 14. Mold for piece-wise continuous three-dimensional convex-concave pier or abutment hydraulic structure corner fairing
  • 3A. Vortex generator assembly
  • 3B. Leading edge ramp vortex generator
  • 3C. Foundation vortex generator

Examples of Scour-Vortex-Preventing SCAUR™ and VORGAUR™ Concepts For Wing-Wall and Spill-Through Abutments

Applications to more types of abutments than shown by the experiments by Simpson et al. (U.S. Pat. No. 8,348,553) are given. In addition to the square-cornered abutments discussed in that patent, scale model tests prove that the scAUR™ fairing with the help of specially designed VorGAUR™ vortex generators prevent scouring vortices for wing-wall and spill-through abutments. Research by Sheppard et al. (2011) using hundreds of sets of scour data and sponsored by the National Co-operative Highway Research Program (NCHRP) shows that model scale bridge scour experiments produce much more severe scour depth to pier size ratios than the scour depth to pier size ratios observed for full-scale cases due to scale effects. Thus, all of the model scale flume tests presented here show more scour that at full scale (Simpson 2013). FIGS. 8-13 show the key results that the scAUR™ and VorGAUR™ products prevent the formation of scouring vortices and scour for wing-wall and spill-through abutments. FIG. 8 shows surface oilflow results for a scAUR™ modified wing-wall abutment with VorGAUR™ vortex generators (VGs). The mixture of yellow artist oil paint and mineral oil flows with the skin friction lines. Yellow streaks are first painted about perpendicular to the flow direction on a black painted surface. The right to left flow causes some oil to be carried downstream in a local flow direction, which can be observed against the black painted surface. FIG. 8 clearly shows that the effects of the scAUR™ and VorGAUR™ products are to bring lower velocity flow up from the flume bottom and prevent the scour around the bottom of the abutment.

FIG. 9 shows the deep scour holes for the same wing-wall abutment without scAUR™ and VorGAUR™. Here X is the stream-wise location, Z is the spanwise location, and L is the dimension of the abutment into the flow. With a scAUR™ modified wing-wall abutment with VGs, there is not only no scour around the model base, but there is no open bed scour hole farther downstream of the model around X/L=2 as shown in FIG. 10. This is due to the effect of VGs on the surface vortex which caused the scour hole farther downstream of the model for the untreated case. The VGs generate counter-rotating vortices which diffuse and reduce the strength of the free-surface generated vortex. No scour occurred around the contraction and near the base of the modified wing wall with VGs. No open bed scour was observed.

Some flow and scour depth results are given for a flume test for a scAUR™ modified spill-through abutment with VorGAUR™ VGs. This test has been performed under the same flow conditions and flume geometry as for the spill-through abutment without scAUR™ and VorGAUR™ products.

FIG. 11 is a surface oilflow for this case that clearly shows that the scAUR™ and VorGAUR™ products bring lower velocity flow up from the flume bottom and prevent scour around the bottom of the abutment (Simpson et al. 2013). FIG. 12 shows the deep scour holes for the unmodified spill-through abutment. With a scAUR™ modified spill-through abutment with VGs, FIG. 13 shows no scour around the upstream contraction and near the base of the modified spill-through abutment due to the fairing. Although there is still a very minor scour at the downstream of the model, its max depth (−0.02 L) is much lower than that for an untreated abutment. The downstream open bed scour due to the free surface vortex has been greatly reduced.

Example for Bridge Piers and Abutments at High Angles of Attack—45 Deg Dogleg Configuration

Here an extension is disclosed for bridge piers and abutments at larger angles of attack of up to 45°. Nose and tail extension sections on a pier form a dogleg shape (FIG. 14) and VorGAUR™ vortex generators prevent separations. The centerline of the piece-wise continuous curved pier nose and tail extensions and the nose and tail of the scAUR™ are aligned with the on-coming flow direction. VorGAUR™ vortex generators are used to energize the near-wall flow upstream of the adverse pressure gradient regions around the pier and prevent separation and scour.

Model scale experiments in the AUR flume were performed that confirm that this design prevents scour. The VGs are attached on both front and rear fairings as shown in FIGS. 15a and 15b. The VGs are 76 mm long and 19 mm high. The free-stream velocity is 0.58 m/s and the flow speed near the VGs on the fairings is about 0.61 m/s, which caused scour when the VGs were not used. As shown in the photos below, there is no scour around the model.

Manufacturing and installation processes and methods would be the same as for bridges at lower angles of attack that do not need the dogleg. However there are increases in costs due to the addition of the additional components required for the SS dogleg on a pier (Simpson 2013).

Example of SCAUR™ with VORGAUR™ for a Swirling River Downstream of a Bend Here another extension is disclosed for bridge piers and abutments downstream of a bend in a river where there is large-scale swirling approach flow produced by the river bend. The fully three-dimensional shape is modified from the straight ahead case to meet the requirement of the design that the stream-wise gradient of surface vorticity flux must not exceed the vorticity diffusion rate in the boundary layer, thus preventing the formation of a discrete vortex. Another requirement is that a minimal size of the fairing be used that meets the first requirement.

FIGS. 16-18 show results for a thick upstream inflow boundary layer. The pier is located downstream of a 90 degree river bend. Pier model width D is 0.076 m wide with a 27.5 mps flow. The inflow boundary layer thickness=0.25 m. The near-river bottom flow moves toward the inner curved river bank under the large pressure gradient between the inner and outer river banks. The near free-surface flow moves toward the outer curved river bank under the effect of flow inertia. A large stream-wise vortex across the entire river is produced by the end of the curved section of the river.

This swirling flow is the upstream inflow to the pier. This inflow allows one to modify the nose shape from the straight ahead case shape and meet the vorticity flux requirement mentioned above. There is no separation or rollup of a discrete vortex that will cause scour.

Example Foundation Scour Vortex Prevention Device: The Curved Leading Edge Ramp

Aspects of the scAUR™ and VorGAUR™ design features have been expanded by using a curved leading edge ramp in front of a pier or abutment foundation in order to further protect the foundation from the effects of contraction scour, long term degradation scour, settlement and differential settlement of footers, undermining of the concrete scAUR™ segments, and effects of variable surrounding bed levels. This leading edge ramp prevents undermining of the foundation when the scAUR™ and VorGAUR™ products are installed on a pier or abutment.

First, when the scAUR™ and VorGAUR™ design features are installed on a bridge pier or abutment, the scAUR™ fairing prevents any scouring horseshoe vortex formation and downflow of higher velocity water from upstream and the VorGAUR™ vortex generators cause low speed water flow near the river bottom next to the pier or abutment to move up the pier or abutment, as shown in FIGS. 8 and 11. Thus, the velocities, shearing stresses on the bottom of the pier or abutment, and pressure gradients will be lower than without the scAUR™ and VorGAUR™. Presumably the surrounding river bed will be at the same height or level as the top edge of the scAUR™ fairing at the bottom of the pier or abutment after installation. As all AUR flume studies have shown, under these conditions scour of the open bed material occurs at a lower river speed before scour of the material around the base of the scAUR™ fairing occurs.

What this means is that scour of the river bed away from the scAUR™ protected pier or abutment will occur first and that the river bed level will be lower away from the pier or abutment. If a pier or abutment foundation is exposed, it will still have a higher immediate surrounding river bed level than farther away. Even so, it is desirable to further arrest scour around the foundation to prevent high speed open bed scour from encroaching on the river bed material next to the foundation.

Second, if the front of the foundation of a pier or abutment is exposed to approach flows, then a foundation horseshoe or scouring vortex is formed at the front which will cause local scour around the pier or abutment. What this suggests is that a curved ramp be mounted in front of the foundation that prevents the formation of this foundation horseshoe vortex. Additional components around the sides of the foundation are also another thought, but since they do not produce a flow that moves up the scAUR™ fairing, they will not produce any benefit.

Based on these facts, flume tests were conducted with 3 foundation leading edge ramp configurations: (1) an exposed rectangular foundation with no front ramp protection, (2) an upstream curved foundation ramp with trapezoidal spanwise edges to produce a stream-wise vortex to bring open bed materials toward the foundation, and (3) a curved upstream foundation ramp with straight span-wise edges. Gravel A, which is the smallest gravel used in the AUR flume and has a specific gravity of 3.7 and the size of 1.18-1.4 mm, are distributed around the scAUR™ model for each test.

Flume tests for scour depth were made for these 3 cases with a H=12.7 mm high foundation elevation (H/D=1/6) with gravel A around the foundation with or without a leading edge ramp (Simpson 2013). These tests were done with a flow speed of 0.6 mps at which the pea gravel in the open bed begins to be carried downstream. Without a ramp, as expected, the scour occurred at the front corners of the model due to the front foundation horseshoe vortex, as shown in FIG. 19. There is gravel accumulation along the pier side near the location of VGs on the scAUR™ fairing on the pier, which is caused by the horseshoe vortices and downstream upflow generated by these VGs.

For the H=12.7 mm high foundation (H/D=1/6) with a curved ramp with trapezoidal sides, the scour occurs at the front corner of the ramp and more gravel accumulates along the pier side around the VGs (Simpson 2013). Furthermore, there is a gravel mound at the downstream model edge. The gravel carried from the upstream are accumulated along the pier side and at the pier end. Therefore, the tested trapezoidal front ramp is not effective to reduce or prevent the scour at the upstream end of the foundation when the edge of the foundation is higher than the surrounding bed.

For the H=12.7 mm high elevation (H/D=1/6) with 19 mm high curved straight-sided ramp, scour around the front of the foundation is not detectable (FIG. 20) since the ramp is submerged 6.4 mm and the blunt nose of the ramp is not exposed to the flow. The scour hole and mound along the side is also minimized. The scour hole along the pier side is away from the pier foundation several piers heights and the gravel accumulate on the pier side downstream of the VG. This is a desired result since no gravel next to the foundation is removed. To the contrary, downstream of the VGs gravel from the open bed is brought toward the foundation edge, which serves to further protect the foundation from further scour. Results for a 19 mm high foundation produced very similar results (Simpson 2013). In summary, all of these foundation tests show that a leading edge straight-sided curved ramp prevents scour around a foundation when there is open bed scour.

Example of Initially Submerged Pier and Abutment Vortex Generators To Protect a Foundation from Open-Bed Scour

In addition to the curved leading edge ramp mentioned above, a further innovation to protect a foundation from open-bed scour uses a vortex generator at 20 degrees angle of attack in front of each leading edge corner of the ramp, which will create a vortex that brings available loose open-bed scour materials toward the pier or abutment foundation to protect the pier or abutment, as shown in FIG. 21 for a pier. Like for the ramp, when there is no high velocity flow and the curved leading edge ramp (7) is covered with river bed material, the vortex generators (3B) are also covered with bed material. When the water flow speed approaching the pier or abutment is large enough to cause open-bed scour, the bed material over the curved leading edge ramp and the vortex generators will eventually be removed exposing both the ramp and vortex generators. Both the curved leading edge ramp and the vortex generators create vortices that bring loose open-bed material toward the foundation to further protect it from scour.

Another innovation uses vortex generators (VG) mounted on the sides of the foundation (3C) to bring more available loose open-bed scour materials toward the pier or abutment foundation to protect further the pier or abutment. These vortex generators are initially submerged below the surface of the river bed, but are exposed when there is high velocity flow and open-bed scour. Properly oriented, they create vortices that bring open-bed scour material towards the foundation for protection.

Example Pier and Abutment Stern or Tail Fairings to Further Prevent Scour

When a pier is in close proximity to an adjacent pier or abutment, the flow between the two hydraulic structures is at a higher speed than if they were further apart. This means that at the downstream region of the pier or abutment there will be a greater positive or adverse stream-wise pressure gradient, which will lead to more and stronger flow separation (FIG. 22). To reduce this separation and possibilities for scour, a more gradual fairing or tail can be used, as shown in FIG. 23 for a pier. A similar more gradual fairing can be used for abutments.

The test with a narrow flume width was conducted without a tail first in order to compare with the tail case. The upstream free-stream flow is 0.56 m/s and the flow speed is about 0.66-0.67 m/s between the model and the side wall. After 50 minutes the scour holes downstream of the model are symmetric on each side of the centerline and are caused by the separated vortices from the rear fairing, as shown in FIG. 22. The corresponding scour deposition mound is located along the centerline. A video clip was recorded for this scour development.

A tail is attached to the rear fairing as shown in FIG. 23 in order to prevent the separation from the rear fairing which causes this scour hole at the downstream of the model. The tail in this example is a NACA0024 airfoil that is 76 mm thick which is the width of model pier, 178 mm long and 203 mm high.

The tail on the model was tested with the same flume conditions as without a tail, 0.56 m/s free-stream velocity and 0.66-0.67 m/s between the model and the side wall. After a 50 minutes run with the same flow speed as before, there are only very minor scour holes generated at the downstream of the model.

Examples of Additional Construction and Mold Materials and Piece-Wise Continuous Concave-Convex Curvature Surfaces

In an extension to Simpson et al. (U.S. Pat. No. 8,348,553), in addition to the concrete or fiber-reinforced composite, or combination thereof, hydrodynamic fairing disclosed in that patent, the present invention in practice is a cast-in-place, pre-cast, or sprayed (“shotcrete”) concrete, metal, or composite material, or combinations thereof, hydrodynamic fairing that is fit or cast over one or more existing or new hydraulic structures around the bases of these structures and above and around their footings. Molds for the concrete or composite fairing are made from wood and other natural materials, metal or composite materials, or combinations thereof. Such a properly designed fairing, as described by Simpson et al. (U.S. Pat. No. 8,348,553), prevents scouring vortex formation for both steady and unsteady flows, including oscillatory tidal flows. The product is manufactured using existing metal, concrete, and composite materials technologies well known to professionals. As such, the product can be produced at minimal cost and with high probability of endurance over a long future period.

While the shape of the scAUR™ for bridge piers and abutments is fully three-dimensional, as described in detail by Simpson et al. (U.S. Pat. No. 8,348,553), it can be approximated by piece-wise continuous concave-convex-curvature surfaces within definable tolerances that produce the same scouring vortex prevention effects as continuous concave-convex-curvature surfaces. No scouring vortices are produced in either case, but the piece-wise continuous curvature version can be manufactured at a much lower cost.

Retrofit SCAUR™ Bridge Pier and Abutment Fairing

An attractive manufacturing alternative for a scAUR™ retrofit bridge fairing uses stainless steel (SS) or even weathering steel. Stainless steel was considered for both the double curvature end sections and the cylindrical sides of the scAUR™. Its corrosion resistance gives it a lifetime of 100 years even in seawater environments, using a proper thickness, construction methods, and type of SS. It is an effective way to reduce weight and the cost associated with casting custom reinforced concrete structures. Another benefit is that the SS VorGAUR™ vortex generators can be welded directly onto the side sections instead of having to be integrated into the rebar cage of a reinforced concrete structure.

Typical example costs for each of these manufacturing approaches were developed from current cost information and quotations from concrete and steel fabricators. It is clear that stainless steel is the best choice for bridge retrofits.

FIGS. 24 and 25 show a full-scale sheet stainless steel retrofit scAUR™ with VorGAUR™ pier fairing with piece-wise continuous concave-convex-curvature surfaces within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces. FIG. 26-30 show full-scale sheet stainless steel scAUR™ with VorGAUR™ retrofit fairings with piece-wise continuous concave-convex-curvature surfaces for a wing-wall and spill-through abutments. These fairings and fairings for a dogleg pier and a pier with a tail fairing are within definable tolerances that produce the same effects as continuous concave-convex-curvature surfaces. Bulkheads under the sheet-metal skin support the piece-wise continuous concave-convex curvature surface.

FIGS. 24, 29, and 30 show the leading edge ramp (7) for piers. FIGS. 24-30 show scour preventing vortex generators 3A, 3B, and 3C for piers and abutments.

New Construction

In the case with new construction, essentially the difference between the way cast-in-place bridge piers and abutments are constructed currently without the scAUR™ products and in the future with the scAUR™ products is that scAUR™ steel forms for the concrete are used, as shown in FIGS. 31-34, 36, and 37 for piers and abutments. All standard currently used concrete construction methods and tools can be used. During the bridge design phases, the bridge pier or abutment foundation or footer top surface width and length would need to be large enough to accommodate the location of the scAUR™ concrete fairing on top. Rebar needed for the scAUR™ would be included in the foundation during its construction. Stainless steel rebar for welding to the stainless steel vortex generators mounting plates on the surface need to be used for specific locations.

Standard methods for assembling forms and pouring the concrete will be used, as discussed in ACI 318-11. The contractor simply needs to replace the currently used forms for the lowest level of the pier or abutment above the foundation with the scAUR™ forms. The scAUR™ steel forms can be mounted and attached to the foundation forms. The tops of the steel scAUR™ forms on opposite sides of a pier can be attached together with steel angle to completely contain the concrete for the foundation and the scAUR™ fairing. Like current methods, after the scAUR™ and foundation concrete has cured sufficiently, the scAUR™ and foundation forms would be removed. Currently used forms for the next higher portions of the pier or abutment can then be mounted in place for further cast-in-place concrete. Estimated incremental costs of adding the scAUR™ fairing to new construction for additional rebar, concrete, labor, scAUR™ forms, and transportation of forms for various width pier construction shows that the new construction cost is about ⅓ of retrofit costs, so the best time to include the scAUR™ fairing on piers is during new construction.

REFERENCES

• American Concrete Institute (ACI) Committee 318. “ACI 318-11: Building code requirements for Structural Concrete.” ACI Standard, 2011.
• Barkdoll, B. D., Ettema, R., and B. W. Melville, Countermeasures to Protect Bridge Abutments from Scour, NCHRP Report 587, 2007.
• Briaud, Jean-Louis, Monitoring Scour Critical Bridges, NCHRP Synthesis 396, 2006.
• Ettema, R., Yoon, Byungman, Nakato, Tatsuaki and Muste, Marian, A review of scour conditions and scour-estimation difficulties for bridge abutments, KSCE Journal of Civil Engineering, Volume 8, Number 6, Pages 643-65, 2004.
• Lagasse, P., Zevenbergen, L., Schall, J., and Clopper, P., Bridge Scour and Stream Instability Countermeasures. FHWA Technical Report Hydraulic Engineering Circular (HEC)-23, 2001.
• Richardson E V, Harrison L J, Richardson J R, Davies S R 1993 Evaluating scour at bridges. Publ. FHWA-IP-90-017, Federal Highway Administration, US DOT, Washington, D.C.
• Sheppard, D. M., Demir, H., and Melville, B., Scour at Wide Piers and Long Skewed Piers, NCHRP-Report 682, 2011.
• Simpson, R. L., Full-Scale Prototype Testing and Manufacturing and Installation Plans for New Scour-Vortex-Prevention scAUR™ and VorGAUR™ Products for a Representative Scour-critical Bridge, NCHRP-IDEA Report 162, 2013.
• Simpson, R. L., Junction Flows, Annual Review of Fluid Mechanics, Vol. 33, pp. 415-443, 2001.
• Tian, Q. Q., Simpson, R. L., and Lowe, K. T., A laser-based optical approach for measuring scour depth around hydraulic structures, 5th International Conference on Scour and Erosion, ASCE, San Francisco, November 7-11, 2010.

Claims

1. A convex-concave fairing for a hydraulic structure comprising:

a piece-wise continuous streamlined fairing surface installed around a perimeter of the hydraulic structure and extending from near the height above a river on the hydraulic structure to a bed of said river surrounding the hydraulic structure, said piece-wise continuous fairing completely enveloping the hydraulic structure and providing a piece-wise continuous faired shape in a direction of flow of the river, wherein the piece-wise continuous streamlined fairing surface comprises a plurality of continuous surfaces that are assembled together to form the piece-wise continuous streamlined fairing surface, and wherein the discontinuity in the piece-wise continuous streamlined fairing surface occurs at the intersection of the plurality of the continuous surfaces;

at least one vortex generator attached to the piece-wise continuous fairing surface along a longitudinal distance of a stern to stern dimension of said piece-wise continuous fairing surface, and being proximal to the bed of the river in a flow region void of adverse pressure gradients that would persist downstream of said vortex generator for at least one length of said generator, so as to energize a portion of near wall flow with higher-momentum outer layer flow to produce a steady, compact separation and wake and prevent formation of scouring vortices within river flow.

2. A fairing as in claim 1, wherein; said hydraulic structure is a bridge abutment.

3. A fairing as in claim 1, wherein: said hydraulic structure is a pier and said vortex generators are positioned on opposed surfaces thereof.

4. A fairing as in claim 1, wherein: said vortex generators are tetrahedral in shape and include four triangular faces, three of which meet at each vertex, and are constructed of cast-in-place, pre-cast, or sprayed concrete, metal, composite, fiber reinforced polymers, or combinations thereof.

5. A piece-wise continuous fairing in claim 1, wherein: the fairing is constructed of cast-in-place, pre-cast, or sprayed concrete, metal, composite, fiber reinforced polymers, or combinations thereof, that is fit or cast over one or more existing or new hydraulic structures around the base of these structures and above and around their footings.

6-7. (canceled)

8. A fairing as in claim 5, wherein: the fairing surface is comprised of elements that are premanufactured and interlock using matching keys or alignment surfaces among individual premanufactured elements.

9. A method for making a convex-concave fairing for a hydraulic structure whose nose and tail sections and dogleg shape prevents the formation of scouring vortices for large river inflow angle of attack of flow passing said hydraulic structure, the method comprising the steps of:

selecting, in accord with computational fluid dynamics and water flume river bed scour studies, a suitable piece-wise continuous streamlined fairing whose nose and tail sections are aligned with the on-coming flow direction, and installing said fairing around a perimeter of said hydraulic structure and extending from a height above said river on said structure to a bed of said river surrounding said structure, said piece-wise continuous fairing completely enveloping said perimeter of said structure and providing a piece-wise continuous faired shape to said hydraulic structure in a direction of flow of said river, wherein the piece-wise continuous streamlined fairing comprises a plurality of continuous surfaces that are assembled together to form the piece-wise continuous streamlined fairing surface, and wherein the discontinuity in the piece-wise continuous streamlined fairing surface occurs at the intersection of the plurality of the continuous surfaces;

attaching vortex generators to surfaces of said piece-wise continuous fairing downstream from a forward upstream portion of the piece-wise continuous streamlined fairing and along a longitudinal distance of a stem to stern dimension of said piece-wise continuous fairing, and being proximal to said river bed in a flow region void of adverse pressure gradients that would persist downstream of said vortex generator for at least one length of said generator, so as to energize a near wall portion of the flow of river current with higher momentum outer layer flow to induce steady, compact separation and wake and thereby oppose formation of scouring vortices within said river flow around said fairing.

10. A method as in claim 9, wherein:

said vortex generators are tetrahedral in shape and include four triangular faces, three of which meet at each vertex.

11-15. (canceled)

16. A fairing as in claim 1, further comprising a ramp upstream of and attached to the piece-wise continuous streamlined fairing surface.

17. A fairing as in claim 16, further comprising a vortex generator in front of each leading edge corner of the ramp.