Scour Formation Research Articles

Numerical Simulation of Pipeline Scour and Sedimentation around Submerged Pipelines with an Open-Source Multiphase-CFD Model

This paper presents a comprehensive study on pipeline scour and sedimentation phenomena using an open-source multiphase Computational Fluid Dynamics (CFD) model. The research focuses on understanding the complex interactions between fluid flow, sediment transport, and scour formation around submerged pipelines. The proposed analysis aims to enhance the understanding of scour development and sedimentation deposition, which is crucial for the design, operation, and maintenance of various engineering structures, including offshore pipelines and underwater infrastructure. The results show that the model exhibits the ability to compute sediment transport without depending on traditional assumptions related to bed-load and suspended-load layers. The simulation results affirm the model's proficiency in replicating the underlying mechanisms accountable for the onset of these processes, notably seepage flow and piping. Furthermore, this model can successfully depict the vortex phenomenon, which promotes the accumulation of sediment around the pipe. This phenomenon arises from the contrast in pressure between the centre of the vortex and the pressure exerted on the sediment beneath it.

Migrating scour depth around a spur dike with downward seepage using multiscale characterizations

The current work uses an experimental method to analyse a multiscale statistical assessment of scour depth surrounding the spur dikes with downward seepage. The experiments used three T-shape spur dikes arranged in three series and provided outward from the channel's bank. A no-seepage condition and two distinct seepage velocities, VS1 = 0.09 mm/s and VS2 = 0.18 mm/s, were used in the experiments. Seepage from a channel affects the morphological behaviour and stability of the channel's bed, leading to changes in its hydrodynamic characteristics. In addition, downward seepage movement shifts the flow near the channel boundary and weakens the particles' stability. Thus, the streamwise velocity and Reynolds shear stress increase near the bed. As the seepage velocity increases, the local scour formation also rises relative to the channel's bed until the channel reaches a state of equilibrium. The celerity of scour depth for both time and length scales depends on the amount of downward seepage. Initially, higher seepage leads to faster changes in the scour depth, but over time, this rate decreases until it becomes constant. The bedform elevations' tails are thicker initially, but they become thinner and closer to the Gaussian distribution curve over time.

TURBULENT BORES–INDUCED SCOUR AND PORE PRESSURE VARIATIONS AROUND A VERTICAL STRUCTURE

The scour due to the highly turbulent tsunami inundation is also a major threat to nearshore infrastructure [Nakamura, et al., 2008]. Research on local sediment erosion during tsunami events has shown a correlation between scour formation, pore pressure variations, and soil liquefaction [Mioduszewski and Maeno, 2003]. To understand the structures’ capacity to withstand the tsunami bores, it is critical to assess scour formation and pore pressure variations around their foundations [Macabuag et al., 2018, Nicholas et al., 2020; Mehrzad et at. 2021]. Young et al. (2008) conducted laboratory experiments to study tsunami induced liquefaction failure on a sand bed with two different slopes of 1V:5H and 1V:15H. The correlation between soil liquefaction and scour showed a direct link with bed slope and pore pressure and the peak pressure increased as the bed slope increased. Concerning the hydrodynamic forcing factor, research conducted by [Chanson, 2006] showed that the hydrodynamic characteristics of tsunami inundation can be adequately modeled using dam-break waves. The prime objective of this study was to comprehensively investigate the interaction of a wide range of hydrodynamic conditions and beach slopes on the variation of the pore pressure and associated scour.

Full continuum approach for simulating plume-surface interaction in planetary landings

A high-fidelity computational framework for predicting the interaction of a rocket plume with a dust blanket in an almost vacuum ambient that represents the descent/ascend phase of planetary landing is developed. Compared to the existing continuum frameworks, the developed tool benefits from nonlinear-coupled constitutive relationships obtained using a method of moments approach to tackle the non-equilibrium effects in the rarefied condition. The two-phase flow is modeled in an Eulerian framework that allows for the simulation of a wider range of solid regimes compared to the Lagrangian counterpart. Simulations were conducted to analyze the cratering phenomena and regolith ejecta dynamics. Moreover, the vorticity growth rates were analyzed using a new vorticity transport equation (VTE) by including the bulk viscosity and multiphase terms to demonstrate the contribution of each term to the formation of counterintuitive festooned patterns on the surface owing to jet impingement. This analysis identified a new contributing mechanism responsible for the scour patterns. Although all the investigated terms in the VTE contribute to such patterns, the viscous term has more effect during the entire investigation period. Furthermore, studies on particulate loading, particle diameter, and bed height were conducted to highlight the role of these parameters on brownout phenomena and scour formation patterns. The simulation results depict that the generated vortex core beneath the nozzle is highly dependent on the diameter of the particles as well as the bed height: an increase in the height of the bed and particle diameter can lead to a more favorable brownout status.

On the Morphodynamics of a Wide Class of Large‐Scale Meandering Rivers: Insights Gained by Coupling LES With Sediment‐Dynamics

AbstractIn meandering rivers, interactions between flow, sediment transport, and bed topography affect diverse processes, including bedform development and channel migration. Predicting how these interactions affect the spatial patterns and magnitudes of bed deformation in meandering rivers is essential for various river engineering and geoscience problems. Computational fluid dynamics simulations can predict river morphodynamics at fine temporal and spatial scales but have traditionally been challenged by the large scale of natural rivers. We conducted coupled large‐eddy simulation and bed morphodynamics simulations to create a unique database of hydro‐morphodynamic data sets for 42 meandering rivers with a variety of planform shapes and large‐scale geometrical features that mimic natural meanders. For each simulated river, the database includes (a) bed morphology, (b) three‐dimensional mean velocity field, and (c) bed shear stress distribution under bankfull flow conditions. The calculated morphodynamics results at dynamic equilibrium revealed the formation of scour and deposition patterns near the outer and inner banks, respectively, while the location of point bars and scour regions around the apexes of the meander bends is found to vary as a function of the radius of curvature of the bends to the width ratio. A new mechanism is proposed that explains this seemingly paradoxical finding. The high‐fidelity simulation results generated in this work provide researchers and scientists with a rich numerical database for morphodynamics and bed shear stress distributions in large‐scale meandering rivers to enable systematic investigation of the underlying phenomena and support a range of river engineering applications.

Effects of collars on local scour around semi-circular end bridge abutments

The occurrence of scour around bridge elements due to the transportation of bed material during flood events can cause serious structural damage and loss of life. Increased uncertainties in precipitation and runoff predictions due to climate change make this phenomenon more complex and dangerous. Bridge scour countermeasures should thus be more focused on decreasing scour formation around bridge elements. In this study, abutment scour under clear-water conditions with constant flow intensity was conducted and collars were tested as scour countermeasures around semi-circular end bridge abutments. The experimental study was performed in a rectangular channel with an almost uniform cohesionless bed material for 3 h with and without collars. Collars of various lengths located at different elevations around the abutments were tested to investigate the effect of collars on scour development. The results of the study showed that the scour depth decreased with increasing collar width and when the collar was placed below the bed level for a given abutment length. The results were compared with those of similar earlier studies to show the effect of abutment shape, size of the bed sediment and test durations on the development of scour depth around abutments.

Effect of armor layer on the local scour formation induced by a deeply submerged circular wall jet in confined channels

A series of laboratory experiments was conducted in a confined channel to study the effect of armor layer on the scour formation induced by a deeply submerged circular turbulent wall jet. A wide range of particle sizes was utilized to form an armor layer and the local erosion downstream of a circular wall jet was measured. The time evolution of scour dimensions was recorded and the scour profiles of the mixed bed were compared with the scour profiles of a relatively uniform sand bed with the same average particle size. Three regimes were identified as the initial stage (Regime I), the quasi-steady state (Regime II), and the steady state (Regime III). The characteristic lengths of the scour showed rapid growth at the early stage of scour development and the growth rate decreased until the scour reached the steady-state condition. The effect of armor layer on scour dimensions was pronounced, which significantly reduced the maximum scour depth due to formation of an armor layer. The characteristic parameters affecting the maximum scour depth and width were identified and empirical correlations were introduced for the prediction of scour dimensions. The scour profiles in the mixed bed showed two consecutive scour depths. It was found that the area occupied by the armor layer increased by increasing the Froude number of the jet.

Experimental study of bed evolution around a non-slender square structure under combined solitary wave and steady current actions

This paper presents the findings from the laboratory wave flume experiments designed to investigate the formation and evolution of scour around a non-slender, square vertical structure, under three flow conditions, solitary wave, combined solitary wave and steady following current, and combined solitary wave and steady opposing current. The structure was placed on a sandy berm, either fastened to the flume wall or positioned at the centerline of the flume. For the wave only case, the scour on the seaside edge turned out to be deeper than the one on the leeside regardless of the structure's position. The analyses showed that the depth, width, volume, and location of the scour were all significantly influenced by the introduction of steady currents. The following current, for example, deepened the seaside scour, while leading to shallower leeside scour holes as a result of the backfilling process. Contrary to the opposing current, which shifted the scour area in the upwave direction, the scour was transported downwave under the effect of the following current. The scour depth was determined to be a function of the structure position and the Keulegan-Carpenter number, whereas the scour width mostly depended on the structure’s position. In this regard, the structure fastened to the wall experienced the widest scour area and the largest volume regardless of the flow condition.

Reconstructing sedimentary processes in a Permian channel–lobe transition zone: an outcrop study in the Karoo Basin, South Africa

AbstractTurbidity currents commonly bypass sediment in submarine channels on the continental slope, and deposit sediment lobes farther down-dip on the flat and unconfined abyssal plain. Seafloor and outcrop data have shown that the transition from bypass to deposition usually occurs over complex zones referred to as channel–lobe transition zones (CLTZs). Recognition of these zones in cores and outcrop remains challenging due to a lack of characteristic sedimentary facies and structures. This paper focuses on Unit E of the Permian Fort Brown Formation in the Karoo Basin, South Africa, in the Slagtersfontein outcrop complex, which has previously been interpreted as a CLTZ. This study integrates thin-section micrographs, sedimentary facies, bed-set and stratigraphic architecture, and palaeoflow directions to achieve a multiscale analysis of CLTZ features. A novel process-based facies scheme is developed to evaluate deposits in terms of the depositional or erosional tendencies of the flows that formed them. This scheme allows bypass to be distinguished from depositional zones by the spatial distribution of certain sediment facies. Areas of net sediment bypass were predominantly marked by erosive sediment facies and a larger variability in palaeoflow direction while depositional areas showed a lower variability in palaeoflow directions. Metre-scale structures in the bypass-dominated area reveal seafloor erosion and scour formation. Field relations suggest the presence of a ∼500 m long mega-scour in the CLTZ. The characteristic structures documented here are applicable for identifying CLTZs in sparse datasets such as outcrops with limited palaeogeographical context and sediment cores obtained from subsurface systems.

Effects of spoiler and piggyback on local scour under single and twin submerged pipes

A series of laboratory experiments was carried out to investigate the effects of spoiler and piggyback on the flow field and local scour formation under single and twin submerged pipes. The shape and orientation of spoiler and piggyback were tested in single and twin pipes with different distances from each other. Three piggyback shapes of rectangular, triangular, and circular were designed and the local scour profiles were measured for five orientation angles of θ = 90, 135, 180, 225, and 270°. Flow visualization was employed to study the effects of spoiler and piggyback on the rear vortex field. The velocity field was measured with an Acoustic Doppler Velocimeter (ADV) probe and the magnitudes of Turbulent Kinetic Energy (TKE) around pipelines were extracted from the time series of velocity data. Quadrant analysis was performed based on velocity data to study the effect of spoilers on turbulent momentum transfer between twin pipes. The energy and momentum coefficients were extracted from velocity profiles indicating significant disruption of velocity field and causing additional drag in the rear pipe. A comparison of the equilibrium bed profiles indicated that the minimum and maximum peak scour depths occurred when a rectangular spoiler with θ = 180° and a circular piggyback with θ = 270° were installed, respectively. The self-burial mechanism was examined by alternating the positions of piggybacks and spoilers in twin pipes. The downstream pipe was buried when either spoiler or piggyback is in the upstream pipe. It was found that the rate of self-burial reduced as the distance between two pipes increased.

Morphology Evolution of Three-Dimensional Scours Under Submerged Jets

Through physical model tests, the three-dimensional morphological features and their scale changes with time were measured and comparatively analyzed during the scouring of a homogeneous granular bed surface using submerged oblique jets. The effects of various flow velocities and water cushion depths on the depth, length, and width of the scour hole were studied. At the early stage of scour formation, the morphological scales changed more dramatically, and the jet impact flow velocity had a more significant effect on the scour hole relative to the depth of the water cushion; for the final scales in all three directions of the scour, the scour depth developed at a more significant rate relative to the length and width of the scour. The correlation between the depth, length, and width of scour hole formation was achieved based on the time-domain variation pattern of scour hole scales. As the jet velocity increased and the depth of the water cushion decreased, the scour gradually developed from a wide-shallow morphology to a narrow-deep morphology; the impact of three-dimensional morphological features of the scour on hole depth gradually became obvious, appearing to inhibit the development of scour depth. The results of the present experimental tests offered an exploratory study of the effect of three-dimensional morphological features on the formation of jet scours, having constituted the basis for more rational analysis and evaluation of energy dissipation for the hydraulic operation in water conservancy projects.

An improved Eulerian method in three-dimensional direct numerical simulation on the local scour around a cylinder

An improved Eulerian method with a novel morphologic model is developed based on the direct numerical simulation (DNS) approach to study the local scour. A movable immersed boundary method is proposed to prescribe the geometry of the riverbed. Two techniques, namely the Simultaneous Bed Adjustment Method (SBAM) and (Segment Plane Method) SPM, are proposed to model the complex time changing geometry of the riverbed. The SBAM technique considers sand sliding in the model and the SPM is an algorithm calculating the geometrical parameter of the complex riverbed. A wind tunnel experiment obeying Reynolds similarity and measuring the pressure in a fixed scour hole is carried out to compare with the numerical results. The results show that the movable immersed boundary method performs well in capturing the local scour and qualitatively agrees with the experimental study in how the scour hole develops. The numerical results also show that the DNS can capture the formation of the local scour in details at the beginning and find that the Reynolds stress u'v’ plays an important role in an erosion at the leading edge of the cylinder. Therefore, the newly improved Eulerian method is a valuable tool for DNS studies of local scour with the implementation of MPI.

Equilibrium scour hole size at setback abutments with varied aspect ratios in floodplains

The key features of the equilibrium scour depth dse, width Wse, length Lse and the volume Vse with large abutment aspect ratios (i.e., abutment width Lc divided by its length L) in floodplain are different compared to narrow abutments. Seven models with Lc/L ranging from 0.125 (narrow abutment) to 4 (very wide abutment) were tested. The results show that the combined effect in terms of the abutment aspect ratio Lc/L is a key parameter with wide abutments. Furthermore, the average equilibrium scour width observed was much larger than previous studies and extends up to 3.5 times the floodplain water depth. This implies the current guideline by FHWA (Federal Highway Administration), (2009) to provide a riprap countermeasure apron width for 2 times the floodplain water depth may be insufficient. The much wider scour formation is caused by the migration of the maximum scour location around wide abutments. The results show generally the scour hole dimensions for setback abutments in compound channel are less than that abutments in rectangular channel under the same flow conditions. To this end, empirical equations, which agree well with the data from the present and previous studies are proposed to predict these characteristics at the equilibrium state.

Particle image velocimetry evaluation of flow-altering countermeasures for local scour around a submerged circular cylinder

The effect of scour countermeasures on the mechanism of local scour around a cylinder requires clarification in order to develop design methodology for use in practice. Previous investigations on countermeasure performance, though useful, have not provided adequate measurements to support this understanding. In the present investigation, particle image velocimetry (PIV) measurements were acquired at several streamwise-vertical planes in the flow field surrounding a submerged circular cylinder with a vertical splitter plate and with a rectangular collar (a horizontal base plate). Analysis of the distribution of mean streamwise velocity and Reynolds shear stress as well as the scour formation indicated that the splitter plate disrupted shear layer interaction in the wake region, reducing the width of scour downstream of the cylinder by 3%. The collar eliminated scour upstream of the cylinder entirely by providing protection at the sides of the cylinder where the shear stress exceeds the critical bed shear stress, and the streamwise velocity distribution in the region between the cylinder and the channel sidewall indicated that installation of a rectangular collar causes flow separation at a point further upstream on the cylinder surface.

Propeller jet flow scour around pile group supported piers

In this study, scouring formation around pile groups with different configurations and exposed to a ship's main propeller jet flow was investigated experimentally. The experiments were conducted in a flume by installing cylindrical piles on a horizontal sand bed. The selected pile configuration was a 3 × 3 square arrangement. Different tests were performed by changing the space between the piles. The effect of the distance between the piles with respect to the densimetric Froude number (Frd) on scour formation was investigated by considering three different propeller rotation speeds (590, 670 and 745 rpm) with 5 and 7 cm pile diameters (d0), using propellers with diameters (Dp) of 6.5 and 10 cm located 10 cm above the sand bed (G) and 10 cm away from the front piles (X). In addition, the 3D global scour-hole geometry was obtained using photogrammetric data collection and analysis techniques. The equilibrium scour hole morphology was described in detail, and the characteristic dimensions of the resulting scour hole were thoroughly analyzed. The equilibrium scour depth of the pile groups was found to depend on the space between piles (Xt), densimetric Froude number and also position of the propeller. The equilibrium (maximum) scour depths around piles with respect to their configuration were larger than the scour depth around a single pile under same flow conditions.

Three‐dimensional submerged wall jets and their transition to density flows: Morphodynamics and implications for the depositional record

AbstractJets that expand from an orifice into an ambient water body represent a basic flow model for depositional environments related to expanding flows. Momentum‐dominated jets evolve into gravity‐dominated density flows. To understand this transition and its sedimentological relevance, three‐dimensional tank experiments with submerged wall jets were conducted, systematically varying parameters such as the initial density difference, bed slope, grain size and sediment supply. Bedform successions could be subdivided into those related to the jet and those related to the density flow. Jet deposits included early‐stage bedforms, scours and mouth bars. Early‐stage bedforms are asymmetrical dunes that spread concentrically from the orifice. Sediment entrainment by eddies from the expanding jets led to the formation of scours and mouth bars. Flows with lesser initial density difference produced more elongate scours. Conversely, scours became deeper for denser incoming flows. Coarser‐grained sediment caused the formation of higher and steeper mouth bars and vice versa. The transition from momentum‐dominated jets to gravity‐dominated density flows occurred approximately at the mouth‐bar crest. Hydraulic jumps were absent in the expanding jet regions and at the transitions to density flows. Instead, complex flow patterns and circulations were inferred from the velocity measurements within the scour and at the mouth‐bar crests. Bedform trains related to the density flow were controlled by the grain size and sediment supply. Coarse‐grained sediment and high supply rates caused strong mouth‐bar aggradation and flow splitting, leading to the formation of bedform trains laterally adjacent to the mouth bar. Fine‐grained sediment and low supply rates caused the formation of bedform trains downflow of the mouth bar. The symmetrical bedforms deposited by the density flows always displayed an in‐phase relationship with the flow, indicating that they were antidunes. The experimental jet deposits resemble successions known from subaqueous ice‐contact fans and deep water channel‐lobe transition zones.

Simulation of flow pattern around series of groynes with different orientations in meandering channels

The mechanism of flow and turbulence around groynes in a meandering channel is very complex phenomena. To simulate the flow pattern around groynes in meanders a 3D numerical model was built with groynes of different inclinations by using ANSYS Fluent. The developed model was verified by the results of experimental study in meanders. Pressure, velocity, stream lines and turbulent kinetic energy for different groyne angles such as 15°, 30°, 45°, 90°, 120° and 150° were compared and analyzed to find the ideal angle configuration for different functions. Streamlines profiles were studied to understand more about the formation of scours and vortices around the groyne. The study of streamline profiles helped in the study of vortex and scours. The most dynamic variation in pressure and turbulent kinetic energy within the contours were found for groynes with 90° orientation. Large numbers of vortices between the groynes were observed for groynes with 15° and 90° orientation and these vortices were observed between the second and third groynes. For groynes in the meandering, the ideal angle for controlling the velocity was found out to be 45°, as it showed very small number of vortices in the groyne field. The results of the study showed that numerical modelling could be used efficiently for the study of flow and turbulence around groynes in meanders.

Prediction of scour around single vertical piers with different cross-section shapes

In the present work, a 3D numerical model is proposed to study local scouring around single vertical piers with different cross-section shapes under steady-current flow. The model solves the flow field and sediment transport processes using a coupled approach. The flow field is obtained by solving the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations in combination with the k-w SST turbulence closure model and the sediment transport is considered using both bedload and suspended load models. The proposed model is validated against the empirical measurements of local scour around single vertical piers with circular, square, and diamond cross-section shapes obtained from the literature. The measurement of scour depth in equilibrium condition for the simulations reveal the differences of 4.6%, 6.7% and 13.1% from the experimental measurements for the circular, square, and diamond pier cases, respectively. The model displayed a remarkable performance in the prediction of scour around circular and square piers where horseshoe vortices (HSVs) have a leading impact on scour progression. On the other hand, the maximum deviation was found in the case of the diamond pier where HSVs are weak and have minimum impact on the formation of local scour. Overall, the results confirm that the prediction capability of the present model is almost independent of the strength of the formed HSVs and pier cross-section shapes.

Morphological characteristics of eco-friendly protected basins downstream of block ramps in river bends

Block ramps are hydraulic structures used to control the sediment transport in rivers and to dissipate flow energy. Moreover, they serve as useful structures to maintain and preserve ecological habitat and to facilitate fish migration. In the past, scour features of both protected and unprotected stilling basins of block ramps have been studied for straight river branches. Sometimes, these structures are placed at channel curves where the flow distribution is characterized by a significant asymmetry, resulting in a scour formation in correspondence with the channel bank, that needs to be carefully predicted and controlled to minimize the risk of a structural failure. Apparently, so far there are no studies focusing on the scour mechanism occurring in protected stilling basins downstream of block ramps in river bends. Hence, this paper aims at investigating the effect of stilling basin protection on the scour process under a combination of different hydraulic conditions, block ramp configurations and locations of the protection structure along the stilling basin. To this end, tests were carried out by placing the block ramp in a curved channel and varying both the flow discharge and the downstream tailwater depth. The downstream stilling basin was protected by introducing a rock sill at various distances from the ramp toe. It has been found that the equilibrium scour morphology mainly depends on hydraulic conditions and it is also influenced by the position of the rock sill in the basin. A classification of different morphological configurations is proposed as well. Finally, an empirical equation is provided to estimate the maximum scour depth under the tested configurations.

Modelling of scour formation using SedFoam, continuum approach

SedFOAM is a two-phase flow solver built upon consecutive laws, based on the CFD toolbox OpenFOAM. The sediment body is considered as a continuum phase. The intergranular and fluid stresses are modeled with the dense granular flow rheology and the k–ϵ turbulent model, respectively. The model setup will be based on an experimental study on the scour due to a water jet subjected to lateral confinement. A comparison study will be made based on precise experimental data by Martino et al. (2019) that will show the advantages and defaults of SedFoam. The objective of this work is to reproduce the digging and filling cycle of the scour formation due to the water jet in a confined canal. The first numerical results show that it needs to use 3D numerical simulations because of the fluctuation of the jet direction induced by the presence of a driven flow cavity.