Use of Large-Eddy Simulation for the bed shear stress estimation over a dune

2019 ◽  
Author(s):  
Adrien Bourgoin ◽  
Sylvain S. Guillou ◽  
Jérôme Thiébot ◽  
Riadh Ata
Keyword(s):  
Shear Stress ◽  
Large Eddy Simulation ◽  
Bed Shear Stress ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Stress Estimation

Quantifying Turbulent Wall Shear Stress in an Arteriovenous Graft Using Large Eddy Simulation

2012 ◽  
Author(s):  
L. D. Browne ◽  
P. Griffin ◽  
M. T. Walsh
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
Secondary Patency ◽  
Arteriovenous Graft ◽  
Venous Anastomosis ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Shear ◽  
Turbulent Wall

Hemodialysis patients require a vascular access capable of accommodating the high blood flow rates required for effective dialysis treatment. The arteriovenous graft is one such access. However, this access type suffers from reduced one year primary & secondary patency rates of 59–90% and 50–82% respectively [1]. The main contributor to the failure of this access is stenosis via the development of intimal hyperplasia (IH) that predominately occurs at the venous anastomosis. It is hypothesized that the resulting transitional to turbulent flow regime within the venous anastomosis contributes to the development of IH. The aim of this study is to investigate the influence of this transitional to turbulent behavior on wall shear stress within the venous anastomosis via the use of large eddy simulation.

scholarly journals Experimental study of wall boundary conditions for large-eddy simulation

2001 ◽  
Vol 446 ◽  
pp. 309-320 ◽  
Author(s):  
IVAN MARUSIC ◽  
GARY J. KUNKEL ◽  
FERNANDO PORTÉ-AGEL
Keyword(s):  
Boundary Layer ◽  
Boundary Condition ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
Boundary Conditions ◽  
Streamwise Velocity ◽  
New Model ◽  
Eddy Simulation ◽  
Large Eddy

An experimental investigation was conducted to study the wall boundary condition for large-eddy simulation (LES) of a turbulent boundary layer at Rθ = 3500. Most boundary condition formulations for LES require the specification of the instantaneous filtered wall shear stress field based upon the filtered velocity field at the closest grid point above the wall. Three conventional boundary conditions are tested using simultaneously obtained filtered wall shear stress and streamwise and wall-normal velocities, at locations nominally within the log region of the flow. This was done using arrays of hot-film sensors and X-wire probes. The results indicate that models based on streamwise velocity perform better than those using the wall-normal velocity, but overall significant discrepancies were found for all three models. A new model is proposed which gives better agreement with the shear stress measured at the wall. The new model is also based on the streamwise velocity but is formulated so as to be consistent with ‘outer-flow’ scaling similarity of the streamwise velocity spectra. It is therefore expected to be more generally applicable over a larger range of Reynolds numbers at any first-grid position within the log region of the boundary layer.

A Dynamic Procedure for Wall-Modeled Large-Eddy Simulation of High Reynolds Number Flows

2011 ◽  
Author(s):  
Soshi Kawai
Keyword(s):  
Reynolds Number ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
High Reynolds Number ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wall Shear ◽  
High Reynolds ◽  
Near Wall

This paper addresses the error in large-eddy simulation with wall-modeling (i.e., when the wall shear stress is modeled and the viscous near-wall layer is not resolved): the error in estimating the wall shear stress from a given outer-layer velocity field using auxiliary near-wall RANS equations where convection is not neglected. By considering the behavior of turbulence length scales near a wall, the cause of the errors is diagnosed and solutions that remove the errors are proposed based solidly on physical reasoning. The resulting method is shown to accurately predict equilibrium boundary layers at very high Reynolds number, with both realistic instantaneous fields (without overly elongated unphysical near-wall structures) and accurate statistics (both skin friction and turbulence quantities).

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.

Quantifying Turbulent Wall Shear Stress in a Stenosed Pipe Using Large Eddy Simulation

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Roland Gårdhagen ◽  
Jonas Lantz ◽  
Fredrik Carlsson ◽  
Matts Karlsson
Keyword(s):  
Shear Stress ◽  
Wall Shear Stress ◽  
Large Eddy Simulation ◽  
Recirculation Zone ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Large Fluctuations ◽  
Time Average ◽  
Wall Shear ◽  
Turbulent Wall

Large eddy simulation was applied for flow of Re=2000 in a stenosed pipe in order to undertake a thorough investigation of the wall shear stress (WSS) in turbulent flow. A decomposition of the WSS into time averaged and fluctuating components is proposed. It was concluded that a scale resolving technique is required to completely describe the WSS pattern in a subject specific vessel model, since the poststenotic region was dominated by large axial and circumferential fluctuations. Three poststenotic regions of different WSS characteristics were identified. The recirculation zone was subject to a time averaged WSS in the retrograde direction and large fluctuations. After reattachment there was an antegrade shear and smaller fluctuations than in the recirculation zone. At the reattachment the fluctuations were the largest, but no direction dominated over time. Due to symmetry the circumferential time average was always zero. Thus, in a blood vessel, the axial fluctuations would affect endothelial cells in a stretched state, whereas the circumferential fluctuations would act in a relaxed direction.

Modelling of Impinging Flow and Heat Transfer in a Confined Narrow Gap

2008 ◽  
Author(s):  
Y. Q. Zu ◽  
Y. Y. Yan
Keyword(s):  
Heat Transfer ◽  
Shear Stress ◽  
Large Eddy Simulation ◽  
Diameter Ratio ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Air Jet ◽  
Shear Stress Transport ◽  
Large Eddy ◽  
Target Spacing

In this paper, the flow and heat transfer characteristics of a circular air jet vertically impinging on a flat plate near to the nozzle (H/d = 1∼6, where H is the nozzle-to-target spacing, d the diameter of the jet) are numerical analyzed using the CFD code FLUENT 6.1.18. The relative performance of seven versions of turbulent models, including the standard k–ε model, the renormalization group k–ε model, the realizable k-ε model, the standard k–ω model, the Shear-Stress Transport (SST) k–ω model, the Reynolds Stress (RS) model and the Large Eddy Simulation (LES), for the prediction of this type of flow and heat transfer is investigated by comparing the numerical results with available benchmark experimental data. It is found that Shear-Stress Transport k–ω model and Large Eddy Simulation time-variant model can give better predictions of fluid flow and heat transfer properties; especially, the SST k–ω model is recommended as the best compromise between the computational cost and accuracy. Using SST k-ω model, the effects of jet Reynolds number (Re), jet plate length-to-jet diameter ratio (L/d), target spacing-to-jet diameter ratio (H/d) and jet plate width-to-jet diameter ratio (W/d) on local Nusselt number (Nu) of the target plate are examined. A correlation for the stagnation Nu is presented.

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