scholarly journals Scour around Bridge Piers: Numerical Investigations of the Longitudinal Biconcave Pier Shape

2018 ◽  
Vol 62 (4) ◽  
pp. 298-304 ◽  
Author(s):  
Bouabdellah Guemou ◽  
Abdelali Seddini ◽  
Abderrahmane Nekkache Ghenim
Keyword(s):  
Shear Stress ◽  
Flow Direction ◽  
Basic Mechanism ◽  
Horseshoe Vortex ◽  
Local Scour ◽  
Bridge Pier ◽  
Bed Shear Stress ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
The Rich

The flow pattern around a bridge pier and the scouring phenomenon are very complicated. The basic mechanism causing local scour is the down-flow at the upstream face of the pier. It is understood that the horseshoe vortex is the key mechanism that leads to the local scour around pier; existing literature revealed that the strength of the down-flow, horseshoe vortex and the wake vortex are greater in the case of square piers compared to circular piers. In this paper we have investigated a new longitudinal biconcave bridge pier shape that reduces better the bed shear stress. For that purpose, a number of numerical simulations have been carried out using a Finite Volume Method (FVM) and for the turbulence model we have chosen the Detached Eddy Simulation (DES) for its capability to capture the rich dynamics of the horseshoe vortex at the upstream junction between the pier and the bed.The present study shows that the new longitudinal biconcave bridge pier shape reduces 10 % to 12 % the bed shear stress at the junction between the pier and the bed in other hand this shape increases the bed shear stress about 20 % but at a distance of D downstream the bridge pier in the flow direction.

Critical bed shear for initial movement of sediments on a combined lateral and longitudinal slope

2004 ◽  
Vol 35 (2) ◽  
pp. 153-164 ◽  
Author(s):  
Subhasish Dey
Keyword(s):  
Shear Stress ◽  
Flow Direction ◽  
Side Wall ◽  
Shear Stresses ◽  
Bed Shear Stress ◽  
Conduit Flow ◽  
Sloping Bed ◽  
Stress Ratios ◽  
Closed Conduit ◽  
Initial Movement

An experimental study on critical bed shear-stress for initial movement of non-cohesive sediment particles under a steady-uniform stream flow on a combined lateral (across the flow direction) and longitudinal (streamwise direction) sloping bed is presented. The aim of this paper is to ascertain that the critical bed shear-stress on a combined lateral and longitudinal sloping bed is adequately represented by the product of critical bed shear-stress ratios for lateral and longitudinal sloping beds. Experiments were carried out with closed-conduit flow, in two ducts having a semicircular invert section, with three sizes of sediments. In laboratory flumes, the uniform flow is a difficult – if not impossible – proposition for a steeply sloping channel, and is impossible to obtain in an adversely sloping channel. To avoid this problem, the experiments were conducted with a closed-conduit flow. The critical bed shear-stresses for experimental runs were estimated from side-wall correction. The experimental data agree satisfactorily with the results obtained from the proposed formula.

Detached Eddy Simulation of Turbulent Flow and Heat Transfer in a Ribbed Duct

2005 ◽  
Vol 127 (5) ◽  
pp. 888-896 ◽  
Author(s):  
Aroon K. Viswanathan ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Flow Direction ◽  
Main Flow ◽  
Detached Eddy Simulation ◽  
Heat Transfer Characteristics ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Main Flow Direction ◽  
Key Features

Detached Eddy Simulation (DES) of a hydrodynamic and thermally developed turbulent flow is presented for a stationary duct with square ribs aligned normal to the main flow direction. The rib height to channel hydraulic diameter (e∕Dh) is 0.1, the rib pitch to rib height (P∕e) is 10 and the calculations have been carried out for a bulk Reynolds number of 20,000. DES calculations are carried out on a 963 grid, a 643 grid, and a 483 grid to study the effect of grid resolution. Based on the agreement with earlier LES computations, the 643 grid is observed to be suitable for the DES computation. DES and RANS calculations carried out on the 643 grid are compared to LES calculations on 963∕1283 grids and experimental measurements. The flow and heat transfer characteristics for the DES cases compare well with the LES results and the experiments. The average friction and the augmentation ratios are consistent with experimental results, predicting values within 10% of the measured quantities, at a cost lower than the LES calculations. RANS fails to capture some key features of the flow.

Numerical investigation of vortex-induced vibration of an elastically mounted circular cylinder with One-degree of freedom at high Reynolds number using different turbulent models

2018 ◽  
Vol 233 (2) ◽  
pp. 443-453 ◽  
Author(s):  
Niaz Bahadur Khan ◽  
Zainah Ibrahim
Keyword(s):  
Reynolds Number ◽  
Flow Direction ◽  
Cross Flow ◽  
Navier Stokes ◽  
Two Dimensional ◽  
Detached Eddy Simulation ◽  
Eddy Simulation ◽  
Flow Around Cylinder ◽  
Reynolds Averaged Navier Stokes ◽  
Turbulent Models

This study presents numerical investigation for flow around cylinder at Reynolds number = 104 using different turbulent models. Numerical simulations have been conducted for fixed cylinder case at Reynolds number = 104 and for cylinder free to oscillate in cross-flow direction, at Reynolds number O (104), mass–damping ratio = 0.011 and range of frequency ratio wt = 0.4–1.4 using two-dimensional Reynolds-averaged Navier–Stokes equations. In the literature, the study has been conducted using detached eddy simulation, large eddy simulation and direct numerical simulation which are comparatively expensive in terms of computational cost. This study utilizes the Reynolds-averaged Navier–Stokes shear stress transport k-ω and realizable k-ε models to investigate the flow around fixed cylinder and flow around cylinder constrained to oscillate in cross-flow direction only. Hydrodynamic coefficients, vortex mode shape and maximum amplitude ( Ay/ D) extracted from this study are compared with detached eddy simulation, large eddy simulation and direct numerical simulation results. Results obtained using two-dimensional Reynolds-averaged Navier–Stokes shear stress transport k-ω model are encouraging, while realizable k-ε model is unable to capture the entire response branches. In addition, broad range of “lock-in” region is observed due to delay in capturing the transition from upper to lower branch during two-dimensional realizable k-ε analyses.

Delayed Detached Eddy Simulation of a Full 3-Dimensional High-Pressure Turbine Stage: Part I — Flow Topology

2018 ◽  
Author(s):  
Dun Lin ◽  
Xiutao Bian ◽  
Xin Yuan ◽  
Xinrong Su
Keyword(s):  
High Pressure ◽  
Horseshoe Vortex ◽  
Wake Vortex ◽  
High Fidelity ◽  
Detached Eddy Simulation ◽  
Tip Leakage Flow ◽  
High Pressure Turbine ◽  
Flow Topology ◽  
Eddy Simulation ◽  
Delayed Detached Eddy Simulation

In this work, the flow inside a high pressure turbine (HPT) stage is studied with the help of a high-fidelity delayed detached eddy simulation (DDES) code. This work intends to study the flow topology in the HPT stage. There are two motivations for this work: On the one hand, high pressure turbines operates at both transonic Mach numbers and high Reynolds numbers, which imposes a challenge to modern computational fluid dynamics (CFD), especially for scale-resolved simulation methods. An accurate and efficient high-fidelity CFD solver is very important for a thorough understanding of the flow physics and the design of higher-efficient HPT. On the other hand, the wake vortex shedding and tip-leakage flow are important origins of turbine losses and unsteadiness. Built on our previous DDES simulations of HPT vane and stage, this work further investigates the flow in a full 3-dimension HPT stage. The flow topology in the HPT stage is delineated by Q-criterion iso-surfaces. The development of the horseshoe vortex and its interaction with induced vortex and wake vortex is discussed. The wake vortex transportation especially its interaction with the rotor horseshoe vortex is investigated. The flow structures in the tip clearance region are also revealed.

Formation of Sand Ripples Under Turbulent Flow Simulated by LES

2010 ◽  
Author(s):  
Yan Cui ◽  
John C. Wells ◽  
Y. Quoc Nguyen
Keyword(s):  
Shear Stress ◽  
Numerical Model ◽  
Three Dimensional ◽  
Sand Wave ◽  
Bed Shear Stress ◽  
Two Dimensional ◽  
Dimensional Model ◽  
Three Dimensional Model ◽  
Eddy Simulation ◽  
Large Eddy

To simulate the initial formation of sedimentary bedforms, constrained to be in hydraulically smooth turbulent flows under bedload conditions, a numerical model based on Large Eddy Simulation (LES) in a doubly periodic domain has been developed. The numerical model comprises three parts. Given the instantaneous bed geometry, the bed shear stress distribution is obtained from a Large-Eddy-Simulation (LES) method coupled with an Immersed-Boundary-Method (IBM). Flux is estimated by the van Rijn’s formula [1]. Finally, evolution of the bed surface is described by the Exner equation. “Two-dimensional bed” [2] and “three-dimensional bed” models employ, respectively, transversely averaged bed shear stress and instantaneous local shear stress to estimate the bedload flux. Based on this model, the evolution of an initial sand wave has been successfully computed. Compared to the “two-dimensional” [2] model, the three-dimensional model leads to a slightly slower propagation and a smaller sand wave. The tendency of the sand wave evolution in three-dimensional model is two-dimensional during the simulated interval.

scholarly journals Hazards due to large wood accumulations: Local scour and backwater rise

2018 ◽  
Vol 40 ◽  
pp. 02003 ◽  
Author(s):  
Isabella Schalko ◽  
Lukas Schmocker ◽  
Volker Weitbrecht ◽  
Robert M. Boes
Keyword(s):  
Shear Stress ◽  
Flood Hazard ◽  
Local Scour ◽  
Bridge Piers ◽  
Bed Shear Stress ◽  
Large Wood ◽  
Flume Experiments ◽  
Governing Parameter ◽  
Bed Material ◽  
Movable Bed

Large wood (LW) in rivers increases the flow variability and provides habitats for various species. During flood events, transported logs can accumulate at river infrastructures and increase the flood hazard. LW accumulations result in an upstream backwater rise and may increase local scour, for instance at bridge piers. Consequently, estimates of the resulting backwater rise and local scour are necessary to improve the flood hazard assessment. This study presents the findings of flume experiments with a movable bed on local scour and backwater rise due to LW accumulations. The approach flow conditions and the bed material were varied systematically for a specific LW accumulation volume. For all experiments, the initial condition for the bed material was defined as weak transport, since the bed shear stress was slightly below the critical bed shear stress for incipient motion. The inflow Froude number was identified as the governing parameter for backwater rise due to LW accumulations. The present study confirms the hypothesis that the resulting local scour reduces backwater rise. For the local scour, the unit discharge and the grain size diameter are the decisive parameters.

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