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This study performed a bridge pier collar comparison for the purpose of reducing scour, while introducing a new collar design. The new collar, referred to as Collar Prototype Number 3, was designed based on an equilibrium scour hole and provides a method of controlling the horseshoe vortex. Numerical modelling was utilized to show the flow field and bed shear stress as a result of using Collar Prototype Number 3. A prototype model of Collar Prototype Number 3 and a flat plate collar were constructed for the purpose of comparing both experimentally under different flow conditions. Collar Prototype Number 3 proved to be an effective device as it reduced scour in terms of the maximum depth downstream of the pier and overall volume, in some instances, by up to 69.7% and 75.7%, respectively. Furthermore, Collar Prototype Number 3 outperformed the flat plate collar, especially because, unlike the flat plate collar, Collar Prototype Number 3 did not experience undermining. [ABSTRACT FROM AUTHOR]

In this study, the flow and heat transfer characteristics of a liquid jet impinging on cylindrical cavity heat sinks with a local body heat source were numerically investigated. The Transition SST turbulence model was validated and adopted. The parameters of structure and flow, including d/D = 2, 3, and 4, h/D = 0.05, 0.10, 0.15, and 0.20, and Re = 5,000, 10,000, and 23,000, were investigated. The results revealed that the adoption of a cylindrical cavity structure can improve the heat transfer capacity of the heat sink. A horseshoe vortex introduced by an inclined jet near the cavity edge region improved the heat transfer performance. The maximum enhancement of the cylindrical cavity heat sink was 11.8% compared with the flat plate heat sink when d/D = 3, h/D = 0.15, and Re = 23,000. [ABSTRACT FROM AUTHOR]

A Large Eddy Simulation model is developed to simulate the hydrodynamics and scour process around a circular cylinder. The Navier-Stokes solver is based on the projection method and a second-order unstructured finite-volume method. A sigma-coordinate system is used to obtain an accurate representation of the evolution of the sediment-water interface. Bed erosion is simulated by solving the sediment continuity equation using a mass-conservating sand-slide algorithm and a bedload transport rate, which is based on a description of physical processes (Engelund & Fredsøe, 1976). Simulations of flow around a vertical cylinder for free-slip bed, rigid bed, and live-bed cases are done. The mean velocity profile and shear stress validate the accuracy of this model. Horseshoe vortex and lee-wake vortex shedding structure are simulated, and the results are thoroughly discussed in depth. The formation and the temporal development of the scour hole and other topographic bed features are successfully reproduced. The current paper reports the first known investigation of both scour evolution and coherent structure using large-eddy simulation. [ABSTRACT FROM AUTHOR]

Abstract Since local scour at bridge piers in rivers and estuaries is a major cause of bridge failure, estimation of the maximum local scour depth is of great importance to hydraulic and coastal engineers. Although numerous studies that focus on scour-depth prediction have been done and published, understanding of the flow and turbulence characteristics of the horseshoe vortex that drives the scour mechanism in a developing scour hole still is immature. This study aims to quantify the detailed turbulent flow field in a developing clear-water scour hole at a circular pier using Particle Image Velocimetry (PIV). The distributions of velocity fields, turbulence intensities, and Reynolds shear stresses of the horseshoe vortex that form in front of the pier at different scour stages (t = 0, 0.5, 1, 12, 24, and 48 h) are presented in this paper. During scour development, the horseshoe vortex system was found to evolve from one initially small vortex to three vortices. The strength and size of the main vortex are found to increase with increasing scour depth. The regions of both the maximum turbulence intensity and Reynolds shear stress are found to form at a location upstream of the main vortex, where the large turbulent eddies have the highest possibility of occurrence. Results from this study not only provide new insight into the complex flow-sediment interaction at bridge piers, but also provide valuable experimental databases for advanced numerical simulations. [ABSTRACT FROM AUTHOR]

Abstract Local scour around bridge piers is one of the main causes of bridge failures. Study of local scour is very significant for the safe design of piers and other civil and marine structures. Despite the subject has been explored for many decades, the numerical developments have been very limited due to the complicated interaction of three-dimensional flow, sediment transport and fluid-particle interaction. In this work, a numerical model based upon the Reynolds Average Navier Stokes Equation (k-ε) approach has been used for predicting the three dimensional flow (3D) around a bridge piers (square and cylinder piers), mounted on a flat and fixed bed. The main aim of this paper is the validation of the numerical model, based upon the previous experimental data. The CFD-numerical tool is proficient to qualitatively reproduce the flow characteristic for different pier shape and features around the pier, such as the upstream vortex (horseshoe vortex) and downstream vortex (vortex shedding in the wake). The outcome of this study can be used developing adequate numerical model to simulate the 2D and 3D turbulent flow past the square and circular piers, which are relevant case-studies for the marine and civil structures supported by pillars. The corresponding numerical results are in good agreement with those extracted from available experimental data. [ABSTRACT FROM AUTHOR]

A numerical study of the influence of flow topology on the heat transfer upstream a single plate-finned tube is presented in this paper. Investigations have been carried out for three fin spacing E/D= 0.13, 0.2, 0.27 and different Reynolds number ReD, ranging from 1400 to 3840 using a computational fluid dynamic code. The results are compared with heat transfer visualization performed by infrared thermography system. It is shown that calculations reproduce correctly the heat transfer distribution and results are very close to the experimental data qualitatively. A strong dependence of the heat transfer on the flow structure is observed by increasing the fin-spacing and the Reynolds number. [ABSTRACT FROM AUTHOR]

A wing-body junction flow of a navigating underwater vehicle is considered to be a crucial source of the flow radiating acoustic noise, which attracts much research interest. In this paper, wing-plate junction flows are experimentally investigated in a low-speed wind tunnel by smoke-wire flow visualizations and time-resolved PIV measurements. To reveal the physical behavior of such flows, smoke-wire flow visualizations are conducted for a laminar wing-plate junction. A novel control strategy is proposed, to accurately locate the suction openings where the streamline is about to roll up to form a vortex in the turbulent junction flows. The control effect is discussed in perspectives of both the time-averaged and instantaneous flow fields. [ABSTRACT FROM AUTHOR]

Flow field characteristics in the neighbourhood of a finite height circular cylinder mounted on a horizontal plate have been investigated numerically. Three-dimensional simulations are carried out for low Reynolds number (Re) incompressible flow using commercial software ANSYS Fluent 14.0. Topological characteristics of the flow have been investigated near the cylinder of aspect ratio (AR) ranging from 0.5 to 3.0 with Re varied in the range from 40 to 300. Time-averaged streamline plots are presented in various planes for different values of AR and Re to understand the flow field characteristics. For a developing flow impinging on the cylinder, flow separation in upstream of cylinder close to the cylinder-bottom wall junction leads to horseshoe vortex formation. Various topological characteristics like saddle, node have been identified in upstream and downstream of the cylinder. Positions of saddles are shown to depend on the values of AR and Re. Development of recirculation region and formations of vortex bubble have been studied in form of their projections on different planes. The variation of mean drag coefficient on the cylinder with Re for different values of AR has also been presented. [ABSTRACT FROM AUTHOR]

Aerodynamic heating in the blunt-fin induced shock wave/boundary layer interaction is investigated by means of numerical simulations. The complex flow pattern on the flat plate is visualized by surface friction lines. The three-dimensional vortical structures and primary shock wave system in the interaction region are demonstrated. The calculated separation length upstream the fin and the heat flux distribution in the centreline are consistent with the experimental observations. The results exhibits quasi-periodic behavior of the interference flow. Both the time-averaged and instantaneous heat flux on the surface of the flat plate and fin are analyzed, respectively. Due to the shock wave and boundary layer interaction, some regions of extremely high peak heating on the flat plate are observed. The formation mechanism of the high peak heating is also discussed. [ABSTRACT FROM AUTHOR]

The quality of the inflow across the propeller is closely related with the hydrodynamic performance and the noise characteristics of the propeller. For a submarine, with a horseshoe vortex generated at the junction of the main body and the appendages, the submarine wake is dominated by a kind of highly non-uniform flow field, which has an adverse effect on the performance of the submarine propeller. In order to control the horseshoe vortex and improve the quality of the submarine wake, the flow field around a submarine model is simulated by the detached eddies simulation (DES) method, and the vortex configuration is displayed using the second invariant of the velocity derivative tensor. The state and the transition process of the horseshoe vortex are analyzed, then a modified method to break the vortex core by a vortex baffle is proposed. The flow numerical simulation is carried out to study the effect of this method. Numerical simulations show that, with the breakdown of the vortex core, many unstable vortices are shed and the energy of the horseshoe vortex is dissipated quickly, and the uniformity of the submarine wake is improved. The submarine wake test in a wind tunnel has verified the effect of the method to control the horseshoe vortex. The vortex baffle can improve the wake uniformity in cases of high Reynolds numbers as well, and it does not have adverse effects on the maneuverability and the speed ability of the submarine. [ABSTRACT FROM AUTHOR]

The article focuses on the study which investigates the significant role played by horseshoe vortex in the problems of local scour around pile foundation with attached controlling ring.

The horseshoe vortex generated around the sail-body junction of a submarine has an important influence on the uniformity of the submarine wake at the propeller disc. In this article, the horseshoe vortex is simulated by the Detached Eddy Simulation (DES) method, and a new method to control the horseshoe vortex by vortex control baffler is proposed. The numerical simulation shows that a kind of attached vortex, with the rotation direction opposite to that of horseshoe vortex, is generated by the vortex control baffler. With the attached vortex, the strength of the horseshoe vortex is significantly reduced. The wind tunnel experiment on a submarine model is carried out, and the axial velocities at the propeller disc of the submarine with and without vortex control baffler are measured by a hot wire anemometer system. It is shown from the experimental results that the vortex control baffler can enhance the uniformity of the wake at the propeller disc, which helps to improve the propeller performance. The engineering applicability of the vortex control baffler is discussed. [ABSTRACT FROM AUTHOR]

A field experiment was specifically designed and conducted to investigate the width of the near-wake recirculation region of a wide and slender model building. Tracer gas was released from the centre of the leeward side of the building. The results suggested that the width of the wake ranged between 0.6 and 1.1 W in the case of the wind normal to the short side and between 0.5 and 0.9 W in the case of the wind normal to the long side of the building. The length of the near-wake recirculation region was also calculated using a simple empirical expression. Both results are in agreement with flow visualisation trials conducted around the same building. Further experiments showed that in the near-wake region higher rates of dispersion occurred, together with increased residence of the pollutant and that the plume in the wake of the building was to some extent bifurcated, due to the effect of the horseshoe vortex. [ABSTRACT FROM AUTHOR]

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