URANS Computations of Shallow Grid Turbulence

This paper describes the unsteady Reynolds-averaged Navier–Stokes (URANS) computations of a quasi-two-dimensional (2D) grid turbulence in shallow open-channel flows, generated downstream of multiple piers aligned at regular intervals over the channel width. In shallow open-channel flows, the vertical confinement of the flow generally suppresses the three dimensionality and attains two-dimensional features with up-cascading of turbulent kinetic energy from small-scale toward large-scale structures. In this study, 2D depth averaged and 3D Reynolds-averaged equations with linear and nonlinear URANS turbulence models are applied to a shallow open-channel flow downstream of multiple piers and numerical results are discussed through a comparison with the experimental results performed by Uijttewaal and Jirka in 2003. We employed 0-equation models and k-ε models for the 2D and 3D computations, respectively. In 2D computations, vortices downstream of the grid occurred synchronously in the computation with both the linear and nonlinear 0-equation models. In the 3D computations, vortex merging and up-cascading of the kinetic energy were captured when artificial disturbance is added at the inlet. The measured decay of the turbulent kinetic energy in the streamwise direction, with a slope of ?1.3, was well captured by computation with the 3D models with inlet disturbance. The flow sensitivity on the inlet disturbance was rather small in the wide range of the disturbance ratios.     

3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. I: Numerical Model

A general-purpose numerical method is developed for solving the full three-dimensional (3D), incompressible, unsteady Reynolds-averaged Navier-Stokes (URANS) equations in natural river reaches containing complex hydraulic structures at full-scale Reynolds numbers. The method adopts body-fitted, chimera overset grids in conjunction with a grid-embedding strategy to accurately and efficiently discretize arbitrarily complex, multiconnected flow domains. The URANS and turbulence closure equations are discretized using a second-order accurate finite-volume approach. The discrete equations are integrated in time via a dual-time-stepping, artificial compressibility method in conjunction with an efficient coupled, block-implicit, approximate factorization iterative solver. The computer code is parallelized to take full advantage of multiprocessor computer systems so that unsteady solutions on grids with 106 nodes can be obtained within reasonable computational time. The power of the method is demonstrated by applying it to simulate turbulent flow at R ? 107 in a stretch of the Chattahoochee River containing a portion of the actual bridge foundation located near Cornelia, Georgia. It is shown that the method can capture the onset of coherent vortex shedding in the vicinity of the foundation while accounting for the large-scale topographical features of the surrounding river reach.     

Three-Dimensional Unsteady RANS Modeling of Discontinuous Gravity Currents in Rectangular Domains

Discontinuous gravity currents in rectangular channels are modeled numerically by solving the 3D unsteady Reynolds-averaged Navier-Stokes (URANS) equations closed with a buoyancy corrected low-Reynolds number (LRN) k-ε model using second-order accurate finite-volume numerics. It is shown that, on moderately fine computational meshes (with ～ 106 grid nodes) and with careful modeling of the near-wall flow, the URANS model can capture the essential large-scale 3D dynamics of gravity current flows, which previously had been resolved only by DNS and/or large-eddy simulation (LES) on very fine computational meshes. These 3D dynamics include the onset of the well-known lobe-and-cleft instability at the current head, the onset of large-scale Kelvin-Helmholtz billows at the head of the gravity current, and the breakdown of the interfacial billows in the rear part of the current head due to intense three-dimensional mixing. The computed results underscore the importance of careful modeling of the near wall flow in URANS simulations. The standard k-ε model with wall functions fails to capture the aforementioned complex 3D dynamics, which are only resolved by the LRN k-ε model on grids that resolve the near-wall region. Furthermore, numerical experiments show that including in the simulation the lateral no-slip end walls of the channel has a profound effect on the accuracy of the computed solutions. End-wall effects enhance the three-dimensionality of the flow, result in increased mixing of the dense and the ambient fluids behind the head of gravity currents, and yield results in good agreement with measurements. On the other hand, when end-wall effects are omitted, by imposing periodicity in the spanwise direction, three-dimensional mixing is suppressed and the breakdown of interfacial billows is significantly underestimated. Grid sensitivity studies are also carried out using three successively refined meshes and show that the URANS LRN model yields grid-converged solutions at affordable computational resources. As URANS modeling requires only a fraction of the computational cost of DNS or LES with near-wall resolution, the present results underscore the potential of unsteady statistical turbulence models for predicting and elucidating the physics of gravity current flows in complex geometries and at Reynolds numbers of engineering relevance.     

3D Unsteady RANS Modeling of Complex Hydraulic Engineering Flows. II: Model Validation and Flow Physics

A chimera overset grid flow solver is developed for solving the unsteady Reynolds-averaged Navier-Stokes (RANS) equations in arbitrarily complex, multiconnected domains. The details of the numerical method were presented in Part I of this paper. In this work, the method is validated and applied to investigate the physics of flow past a real-life bridge foundation mounted on a fixed flat bed. It is shown that the numerical model can reproduce large-scale unsteady vortices that contain a significant portion of the total turbulence kinetic energy. These coherent motions cannot be captured in previous steady three-dimensional (3D) models. To validate the importance of the unsteady motions, experiments are conducted in the Georgia Institute of Technology scour flume facility. The measured mean velocity and turbulence kinetic energy profiles are compared with the numerical simulation results and are shown to be in good agreement with the numerical simulations. A series of numerical tests is carried out to examine the sensitivity of the solutions to grid refinement and investigate the effect of inflow and far-field boundary conditions. As further validation of the numerical results, the sensitivity of the turbulence kinetic energy profiles on either side of the complex pier bent to a slight asymmetry of the approach flow observed in the experiments is reproduced by the numerical model. In addition, the computed flat-bed flow characteristics are analyzed in comparison with the scour patterns observed in the laboratory to identify key flow features responsible for the initiation of scour. Regions of maximum shear velocity are shown to correspond to maximum scour depths in the shear zone to either side of the upstream pier, but numerical values of vertical velocity are found to be very important in explaining scour and deposition patterns immediately upstream and downstream of the pier bent.     

Investigations on Flow Pattern and Pressure inside SEN below Stopper Rod

In continuous casting of steel, the casting rate is often controlled by a stopper rod placed in the tundish outlet where the submerged entry nozzle (SEN) tube begins. The flow pattern inside the SEN plays an important role for the bubble formation at the argon injection nozzle at the stopper rod tip. High flow velocities are reached in the small gap between stopper rod and the surrounding SEN walls, and a flow separation has to be expected after the gap due to the fast expansion of the cross section. According to theoretical considerations and to the simulations, the absolute pressure in the gap becomes very low for liquid steel, which can cause cavitation‐like effects. PIV‐flow measurements in a 1:1 scaled water model of the caster show a highly oscillating and asymmetric flow pattern with rapidly changing separation regions. The low pressure effects expected in liquid steel cannot be investigated on the water‐model due to the lower density of water. In numerical simulations of the water‐model, the choice of the turbulence model and the usage or the non‐usage of geometrical symmetries for the bound of the computational domain have a great impact on the resulting flow pattern and the accuracy of the predicted pressure drop. The results of various turbulence models are compared with results from measurements on a water‐model. It turns out that only a 3D model using advanced turbulence models (SST k‐ω or Large Eddy) produce acceptable results, while 2D simulations completely fail and the standard turbulence models (e.g. k‐ε) significantly underestimate the pressure drop even in a 3D simulation.     

Characteristics of Horseshoe Vortex in Developing Scour Holes at Piers

The outcome of an experimental study on the turbulent horseshoe vortex flow within the developing (intermediate stages and equilibrium) scour holes at cylindrical piers measured by an acoustic Doppler velocimeter (ADV) are presented. Since the primary objective was to analyze the evolution of the turbulent flow characteristics of a horseshoe vortex within a developing scour hole, the flow zone downstream of the pier was beyond the scope of the investigation. Experiments were conducted for the approaching flow having undisturbed flow depth ( = 0.25?m) greater than twice the pier diameter and the depth-averaged approaching flow velocity ( = 0.357?m/s) about 95% of the critical velocity of the uniform bed sand that had a median diameter of 0.81?mm. The flow measurements by the ADV were taken within the intermediate (having depths of 0.25, 0.5, and 0.75 times the equilibrium scour depth) and equilibrium scour holes (frozen by spraying glue) at a circular pier of diameter 0.12?m. In order to have a comparative study, the ADV measurements within an equilibrium scour hole at a square pier (side facing the approaching flow) of sides equaling the diameter of the circular pier were also taken. The contours of the time-averaged velocities, turbulence intensities, and Reynolds stresses at different azimuthal planes (0, 45, and 90°) are presented. Vector plots of the flow field at azimuthal planes reveal the evolution of the characteristics of the horseshoe vortex flow associated with a downflow from intermediate stages to equilibrium condition of scour holes. The bed-shear stresses are determined from the Reynolds stress distributions. The flow characteristics of the horseshoe vortex are discussed from the point of view of the similarity with the velocity and turbulence characteristic scales. The imperative observation is that the flow and turbulence intensities in the horseshoe vortex flow in a developing scour hole are reasonably similar.     

板坯连铸结晶器内非对称涡流的水模拟研究

利用水模拟研究连铸操作工艺对板坯结晶器液面涡流的影响规律。在实验室进行了不同工艺参数下的试验,分析不同工艺参数对涡流的影响。结果表明,结晶器液面形成涡流的原因主要来自于表面液流的湍动性所导致的水口两侧表面液流动能瞬时的不对称,以及浇注工艺所导致的水口两侧出流及表面液流不对称。在结晶器液面,涡流出现形式分为水口一侧单涡流,一侧双涡流和对角双涡流等情况。上述现象与水口周围液流流态有关,涡流的"强度"(文中用涡流直径和长度表征)以及其出现的频度均随表面液流的动量增大而增加,加大水口浸入深度或增大出流角度有利于减小涡流强度和出现频度。     

Flow Structure at Different Stages in a Meander-Bend with Bendway Weirs

Streambank erosion is an important management issue, particularly for meandering rivers. Recently, bendway weirs have become popular control measures for bank erosion along small meandering streams in the agricultural Midwest. Although these structures have successfully mitigated bank erosion in some cases, there is evidence that the weirs do not always perform as anticipated. Scientific understanding of how bendway weirs influence flow dynamics, streambank erosion, and aquatic habitat is limited. Current design criteria are based primarily on expert judgment rather than a formalized technical design procedure. At field-scale studies, the present paper represents a first step toward an integrated geomorphological and engineering evaluation of the performance of bendway weirs in rivers. To accomplish this initial phase, three-dimensional (3D) velocity data were collected on Sugar Creek at Brookside Farm, Ill., and 3D numerical simulations for low-flow conditions were performed to validate the computational fluid dynamic model. Overall results show good agreement between measured and simulated data for streamwise velocities and turbulence kinetic energy. The model is less accurate at predicting the velocity and turbulence kinetic energy in the shear layer immediately downstream from the weir tips. Based on the validation for low-flow condition, 3D simulations were carried out for medium and high flows where the bendway weirs are completely submerged. These simulations indicate that 3D patterns of flow, especially flow near the outer bank, change dramatically with changes in flow stage. Flow patterns at high-flow condition indicate that bank retreat over the tops of weirs is associated with locally high-shear stresses, thus producing a “shelf” along the base of the outer bank as observed in the field.     

Validation of a Large-Eddy Simulation Model to Simulate Flow in Pump Intakes of Realistic Geometry

This paper describes efforts toward developing a reliable numerical model to predict pump intake flow and associated vortices. Numerical prediction of these flows characterized by the formation of unsteady (meandering) intermittent vortices and presence of massive separation is very challenging. Successful prediction of these phenomena and their effects on the mean flow fields requires numerical methods and turbulence models that can accurately capture the dynamics of the main coherent structures in these flows. In the present work, large-eddy simulation (LES) in conjunction with an accurate nondissipative nonhydrostatic Navier-Stokes massively parallel solver is used to predict the flow and vortical structures in a pressurized pump intake of complex geometry. The LES model is validated using particle image velocimetry data recently collected on a laboratory model of a realistic geometry pump intake. To better put in perspective the predictive performance of the LES model, results from steady simulations employing the shear stress transport (SST) Reynolds-averaged-Navier-Stokes (RANS) model are presented and compared with LES. It is shown that even if SST can fairly successfully capture the mean velocity distribution and mean vortical structures in some regions, overall LES can more accurately predict the mean flow and turbulence statistics compared to the steady SST model.     

Numerical Evaluation of Wind Flow over Complex Terrain: Review

This paper reviews the current state of the art in the numerical evaluation of wind flow over different types of topographies. Numerical simulations differing from one another by the type of numerical formulation followed, the turbulence model used, the type of boundary conditions applied, the type of grids adopted, and the type of terrain considered are summarized. A comparative study among numerical and experimental (both wind tunnel and field) existing works establishing the modifications of wind flow over hills, escarpments, valleys, and other complex terrain configurations demonstrates generally good predictions on the upstream but problematic predictions on the downstream areas of the complex terrain. Comparisons are also made with provisions of the current wind standards as well as with speed-up values calculated using guidelines derived from theoretical models.     

Coherent Structure Dynamics in Turbulent Flows Past In-Stream Structures: Some Insights Gained via Numerical Simulation

Large-scale coherent vortical structures in natural streams and rivers dominate flow and transport processes and impact the stability of stream banks, the diversity and abundance of organisms, and the quality of running waters in aquatic ecosystems. Thus, understanding and being able to model the dynamics of energetic coherent structures in such flows at ecologically relevant scales are crucial prerequisites for developing a science-based ecosystem restoration framework. We review recent progress toward the development of coherent-structure-resolving (CSR) computational fluid dynamics techniques, based on hybrid URANS/LES modeling strategies, for simulating turbulent flows in open-channels with hydraulic structures. CSR simulations of the turbulent horseshoe vortex (THSV) past bed-mounted piers explained the physical mechanism leading to the experimentally documented bimodal velocity fluctuations of the vortex and underscored the importance of the Reynolds number as a key parameter governing the THSV dynamics. Simulations of high Reynolds number flows past surface-piercing, groynelike structures in open channels revealed the complexity of the recirculating region at the upstream face of the groyne, underscored the interaction of the flow in this region with the energetic shear layer shed from the point of separation at the upstream side wall, and demonstrated the importance of flow depth in the vorticity dynamics of such flows. The paper also identifies areas for future work and modeling challenges that need to be addressed for the computational tools to be able to accurately predict flow and transport processes in real-life aquatic environments.     

Steady and Unsteady Simulations of Turbulent Flow and Transport in Ultraviolet Disinfection Channels

The effects of unsteadiness in the turbulent flow through a staggered array of circular cylinders, modeling an ultraviolet disinfection system, are studied by means of solutions of the two-dimensional Reynolds-averaged Navier–Stokes equations incorporating the standard k–? turbulence model. Time averaging is applied to the unsteady solution, and the time-averaged characteristics are compared with a solution where a steady flow is a priori assumed, as well as with time-averaged measurements. Differences between the predictions of time-averaged and the steady-flow models are found to be largest in the entrance region of the array, and to decline in importance in the downstream direction. Comparison with measurements indicate that, while the time-averaged unsteady model predictions exhibited better agreement in some respects, the turbulent kinetic energy remained substantially underpredicted. Predictions of head losses through the array are also discussed.     

Large Eddy Simulation for Unsteady Turbulent Field in Thin Slab Continuous Casting Mold

The unsteady turbulent flow during the continuous casting of steel is important, because it influences critical phenomena that affect steel quality. Unsteady three-dimensional flow in the mold region of the liquid pool during continuous casting of steel slabs has been computed using realistic geometries starting from the submerged inlet nozzle to the mold. The cassette filter function was used to deal with unsteady Navier-Stokes equation, and then the turbulent flow in the thin slab CCM was simulated with the large eddy simulation method combined with the Smagorinsky sub-grid scale model in this paper. And the model was verified by the Particle Image Velocimetry (PIV) experimental results which was got from a relate scientific literature. In this thesis, by means of LES, the flow characteristics in the thin slab CCM were acquired, such as the vortex distribution, the formation of the large eddy coherent structures, development, shedding and fracture process. In the same time, the turbulent asymmetric distribution was revealed even the nozzle in the centre position. Interactions between the two halves cause large velocity fluctuations near the meniscus. And the vortex is located at the low velocity side adjacent to the SEN. Along with the unsteady time development, the unsteady turbulent large vortex structures of the liquid steel in the CCM presented periodic bias flow distribution, and the period is about 20 seconds.     

Mathematical simulation of fluid dynamics during steel draining operations from a ladle

Fluid flow dynamics during ladle drainage operations of steel under isothermal and nonisothermal conditions has been studied using the turbulence shear stress transport k-ε model (SST k-ω) and the multiphase volume of fluid (VOF) model. At high bath levels, the angular velocity of the melt, close to the ladle nozzle, is small rotating anticlockwise and intense vertical-recirculating flows are developed in most of the liquid volume due to descending steel streams along the ladle vertical wall. These streams ascend further downstream driven by buoyancy forces. At low bath levels, the melt, which is close to the nozzle, rotates clockwise with higher velocities whose magnitudes are higher for shorter ladle standstill times. These velocities are responsible for the formation and development of a vortex on the bath free surface, which entrains slag into the nozzle by shear-stress mechanisms at the metal-slag interface. The critical bath level or bath height for this phenomenon is 0.35 m (in this particular ladle design) for a ladle standstill time of 15 minutes and decreases with longer ladle standstill times. At these steps, the vertical-recirculating flows are substituted by complex horizontal-rotating flows in most of the liquid volume. Under isothermal conditions, the critical bath level for vortex formation on the melt free surface is 0.20 m, which agrees very well with that determined with a 1/3 scale water model of 0.073 m. It is concluded that buoyancy forces, originated by thermal gradients, as the ladle cools, are responsible for increasing the critical bath level for vortex formation. Understanding vortex mechanisms will be useful to design simple and efficient devices to break down the vortex flow during steel draining even at very low metal residues in the ladle.     

Timescale Behavior of the Wall Shear Stress in Unsteady Laminar Pipe Flows

Based on two-dimensional (2D) flow model simulations, the effects of the radial structure of the flow (e.g., the nonuniformity of the velocity profile) on the pipe wall shear stress, τw, are determined in terms of bulk parameters such as to allow improved 1D modeling of unsteady contribution of τw. An unsteady generalization, for both laminar and turbulent flows, of the quasi-stationary relationship between τw and the friction slope, J, decomposes the additional unsteady contribution into an instantaneous energy dissipation term and an inertial term (that is, based on the local average acceleration-deceleration effects). The relative importance of these two effects is investigated in a transient laminar flow and an analysis of the range of applicability of this kind of approach of representing unsteady friction is presented. Finally, the relation between the additional inertial term and Boussinesq momentum coefficient, is clarified. Although laminar pipe flows are a special case in engineering practice, solutions in this flow regime can provide some insight into the behavior of the transient wall shear stress, and serve as a preliminary step to the solutions of unsteady turbulent pipe flows.     

Purging of a Neutrally Buoyant or a Dense Miscible Contaminant from a Rectangular Cavity. I: Case of an Incoming Laminar Boundary Layer

The flow past two-dimensional (2D) channel cavities along with the removal of neutrally buoyant or dense miscible contaminants introduced instantaneously inside the cavity are studied using eddy resolving techniques. In the simulations, the incoming boundary layer is laminar and the flow is observed not to transition to turbulence as it is convected over the cavity. As for these flow conditions the main coherent structures in the separated shear layer over the cavity are quasi-dimensional, 2D simulations are performed. It is found that the mechanism of removal of the contaminant is very different between the neutrally buoyant and buoyant cases. In the neutrally buoyant case the contaminant is purged from the cavity mostly due to the interactions between the vortices shed in the separated shear layer with the main recirculation eddies inside the cavity and with the trailing edge corner. In the simulations in which a dense contaminant is introduced inside the cavity, after the initial stages of the mass exchange process, the main phenomenon is the presence of a large amplitude internal wave motion which interacts with a strong cavity vortex situated near the trailing edge corner in between the shear layer and the density interface. The density variation across this oscillatory interface is strong. Through this interaction wisps of denser contaminant are extracted from the region beneath the density interface, before being ejected from the cavity by the separated shear layer vortices. The values of the global mass exchange coefficients for the different phases of the purging process are estimated from simple dead-zone models. As expected, the purging process is delayed in the case in which the density of the contaminant is larger than the one of the carrying fluid.     

Fluid flow in pachuca (air-agitated) tanks: Part I. Laboratory-scale experimental measurements

Gas-agitated reactors are used in a number of process industries, including the metallurgical industry, where they are known as “Pachuca” tanks. In spite of the fact that it is the circulation (i.e., velocity and turbulent kinetic energy distribution) within these tanks that governs the main process requirements,i.e., mass transfer and particle suspension, very little attention has been paid to the question of fluid flow. In the present study, velicity measurements made in a laboratory-scale Pachuca tank have suggested the importance of the fluid flow pattern in governing the performance of air-agitated tanks and have shed some light on the efficient operation of these tanks. Full-center-column tanks with large tank height-to-diameter ratios have a “near-stagnant zone” in the lower section of the annulus. The stagnant zone is a region of low turbulent kinetic energy and is undesirable, since it costs energy and is likely to provide very little in return in terms of mass transfer. An increase in the draft tube diameter, for a given tank diameter, leads to higher velocity and turbulence levels in the annulus, which, in turn, should promote mass transfer. Free-airlift tanks seem to be more vigorously agitated than full-center-column tanks. The present study shows that operating a full-center-column Pachuca tank with the liquid surface at or below the same level as the draft tube top would be disadvantageous in terms of particle suspension and mass transfer and also illustrates that it is erroneous to correlate the turbulence on the liquid surface with the turbulence level within the tank.     

CFD Benchmark for a Single Strand Tundish (Part I)

A Computational Fluid Dynamic (CFD) benchmark for the water model of a single‐strand continuous casting tundish was performed by ten members of the newly founded working group “Fluid Mechanics and Fluid Simulation” of the German Steel Institute VDEh. A critical comparison is drawn between laser‐optical velocity measurements and residence time measurements on the one hand and CFD simulations using different CFD programs, turbulence models, boundary conditions, proposed solutions, etc., on the other hand. The validation criteria used include, among others, the turbulence distribution, the position of the recirculation center and the maximum backflow velocity in the tundish which is induced by the recirculation, as well as the residence time distribution. The results show that the flow and turbulence structure can be computed on the basis of the Unsteady Reynolds averaged Navier‐Stokes (URANS) equations with a good degree of accuracy. The relative positional deviation of the recirculation center is ‐12.5% < Δx/L₁ < 5.0%. The characteristic times Θ_min, Θ_max, Θ_20% and Θ_5% , which describe the residence time distribution, are established with a variation of ±15%. The benchmark yields important results for the sensible use of today's commonly used numerical CFD models and contributes to further improving the reliability of CFD simulations in metallurgical process engineering.     

Turbulent flow field over fluvial obstacle marks generated in a laboratory flume

The study is aimed at investigating the mean flow and turbulence characteristics in scour geometry developed near a circular cylinder of length 10cm placed over the sand bed transverse to the flow. The obstacle placed on a sand bed, on the way of a unidirectional flow, develops a crescent-shaped scour mark on the bed. The scour is caused by generation of vortex developed on the upstream side of the obstacle. Sand grains eroded by this vortex, are deposited on the downstream side of the obstacle as wakes. The turbulent flow field within the scour mark was measured in a laboratory flume using an Acoustic Doppler Velocimeter (ADV). The scour marks named as current crescents preserved in geological record are traditionally used as indicators of palaeocurrent direction. The distribution of mean velocity components, turbulent intensities and Reynolds stresses at different positions of the mark are presented. The experimental evidence also shows that the geometric characteristics of the scour mark (width) depend primarily on the cylinder aspect ratio, cylinder Reynolds number and sediment Froude number.     

Detached Eddy Simulation Investigation of Turbulence at a Circular Pier with Scour Hole

This paper uses results from detached eddy simulation to reveal the dynamics of large-scale coherent eddies in the flow around a circular pier with an equilibrium scour hole. This is important for the sediment transport because the local scour process is controlled to a large extent by the large-scale coherent structures present in the near-bed region. The present paper investigates the dynamics of these coherent structures, their interactions and their role in entraining sediment in the later stages of the scour process when the horseshoe vortex system is stabilized by the presence of a large scour hole. The pier Reynolds number was 2.06×105, outside the range of well-resolved large-eddy simulation (LES). Additionally, scale effects are investigated based on comparison with LES results obtained at a much lower Reynolds number of 16,000 in a previous investigation. The paper provides a detailed study of the dynamics of the main necklace vortices of the horseshoe vortex system, including an investigation of the bimodal oscillations, their effect on the amplification of the turbulence within the scour hole and the interactions of the necklace vortices with the downflow. Several mechanisms for the growth of the downstream part of the scour hole in the later stages of the scour process are discussed. Similar to the low-Reynolds-number simulation, and consistent with experimental observations, the presence of strong upwelling motions near the symmetry plane resulted in the suppression of the large-scale vortex shedding in the wake. The fact that the nondimensional values of the turbulent kinetic energy and pressure RMS fluctuations in the higher Reynolds number simulation were consistently lower inside the regions of high turbulence amplification associated with the main necklace vortex, the separated shear layers and the near-wake shows that changes in the flow and turbulence due to the Reynolds number and scour hole geometry can be quantitatively significant over Reynolds numbers between 104 and 105.