scholarly journals Modeling of Flow Around Vegetated Meandering River Reaches

2018 ◽  
Vol 203 ◽  
pp. 07008
Author(s):  
Akihiko Nakayama ◽  
Huan Tao Goh ◽  
Zafarullah Nizamani
Keyword(s):  
Large Eddy Simulation ◽  
Flow Velocity ◽  
Secondary Flow ◽  
Calculation Method ◽  
Curved Channel ◽  
River Flows ◽  
Meandering River ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Artificial Vegetation

Models required in a large eddy simulation of natural river flows which are influenced by the complex bed geometry and the vegetation are proposed. First the model and the calculation method have been applied to a laboratory flow in a curved channel with artificial vegetation. The effects of vegetation on the secondary flow are confirmed to be reproduced correctly. The method is then used to simulate the flow around a real meandering river with vegetation along the banks and on the bars. The results appear reasonable and important characteristics around the bends such as varying flow velocity and the bed shear are also reproduced.

scholarly journals Effects of Riparian Vegetation on the Transport and Accumulation of Floating Objects in a Meandering River

2018 ◽  
Vol 65 ◽  
pp. 07003 ◽  
Author(s):  
Nakayama Akihiko ◽  
Huan Tao Goh ◽  
Seak Ni Chai
Keyword(s):  
Large Eddy Simulation ◽  
Riparian Vegetation ◽  
River Flows ◽  
Meandering River ◽  
Eddy Simulation ◽  
Solid Objects ◽  
Large Eddy ◽  
Floating Objects

In order to study and understand the characteristics of transport and depositions of floating objects in real rivers, Large Eddy Simulation (LES) method of real river flows with complex bathymetry, the riparian vegetation and the floating objects has been developed and applied to a meandering river in Perak, Malaysia. The movement and accumulation of floating objects are different for different sizes and the shapes of the objects. The vegetation that may exists on the bed and the banks also are seen to influence the positions where the objects are accumulated and deposited. The results can be used to control the increasing amount of solid objects washed into the rivers and to the ocean.

Investigation of Fully Developed Turbulent Flow in a Straight Duct With Large Eddy Simulation

1994 ◽  
Vol 116 (4) ◽  
pp. 677-684 ◽  
Author(s):  
M. D. Su ◽  
R. Friedrich
Keyword(s):  
Reynolds Number ◽  
Large Eddy Simulation ◽  
Turbulent Flow ◽  
Secondary Flow ◽  
Initial Conditions ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Fully Developed Turbulent Flow ◽  
High Reynolds ◽  
Straight Duct

Large eddy simulations have been performed in straight ducts with square cross section at a global Reynolds number of 49,000 in order to predict the complicated mean and instantaneous flow involving turbulence-driven secondary motion. Isotropic grid systems were used with spatial resolutions of 256 * 642. The secondary flow not only turned out to develop extremely slowly from its initial conditions but also to require fairly high resolution. The obtained statistical results are compared with measurements. These results show that the large eddy simulation (LES) is a powerful approach to simulate the complex turbulence flow with high Reynolds number. Streaklines of fluid particles in the duct show the secondary flow clearly. The database obtained with LES is used to examine a statistical turbulence model and describe the turbulent vortex structure in the fully developed turbulent flow in a straight duct.

Large Eddy Simulation of Flow and Heat Transfer in a Staggered 45° Ribbed Duct

2004 ◽  
Author(s):  
Samer Abdel-Wahab ◽  
Danesh K. Tafti
Keyword(s):  
Heat Transfer ◽  
Large Eddy Simulation ◽  
Secondary Flow ◽  
Mean Flow ◽  
Cross Sectional ◽  
Heat Transfer Augmentation ◽  
Eddy Simulation ◽  
Flow And Heat Transfer ◽  
Large Eddy ◽  
Rib Vortex

Results from large eddy simulation (LES) of fully developed flow in a staggered 45° ribbed duct are presented with rib pitch-to-height ratio P/e = 10 and a rib height to hydraulic diameter ratio e/Dh = 0.1. The nominal Reynolds number based on bulk velocity is 47,300. Mean flow and turbulent quantities, together with heat transfer and friction augmentation results are presented. The flow is characterized by a helical vortex behind each rib and a complementary cross-sectional secondary flow, both of which result from the angle of the rib with respect to the mean flow. Averaged velocity profiles at the duct center show excellent agreement with experiments and heat transfer predictions agree well with experiments. Turbulent kinetic energy, shear stress, and heat transfer augmentation ratios show a strong correlation to the rib vortex and the secondary flow. Overall, heat transfer is augmented by a factor of 2.3 compared with a smooth duct and matches experimental data within 2%.

Large Eddy Simulation of Lock-Exchange Flow in a Curved Channel

2012 ◽  
Vol 138 (1) ◽  
pp. 57-70 ◽  
Author(s):  
M. Mahdinia ◽  
B. Firoozabadi ◽  
M. Farshchi ◽  
A. Ghasemi Varnamkhasti ◽  
H. Afshin
Keyword(s):  
Large Eddy Simulation ◽  
Exchange Flow ◽  
Curved Channel ◽  
Eddy Simulation ◽  
Large Eddy

scholarly journals Large-Eddy Simulation and RANS Analysis of the End-Wall Flow in a Linear Low-Pressure Turbine Cascade, Part I: Flow and Secondary Vorticity Fields Under Varying Inlet Condition

2019 ◽  
Vol 141 (12) ◽  
Author(s):  
Richard Pichler ◽  
Yaomin Zhao ◽  
Richard Sandberg ◽  
Vittorio Michelassi ◽  
Roberto Pacciani ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Large Eddy Simulation ◽  
Secondary Flow ◽  
Low Pressure ◽  
Eddy Simulation ◽  
Wall Boundary Layer ◽  
Wall Boundary ◽  
Large Eddy ◽  
Wall Flow ◽  
End Wall

Abstract In low-pressure turbines (LPTs), around 60–70% of losses are generated away from end-walls, while the remaining 30–40% is controlled by the interaction of the blade profile with the end-wall boundary layer. Experimental and numerical studies have shown how the strength and penetration of the secondary flow depends on the characteristics of the incoming end-wall boundary layer. Experimental techniques did shed light on the mechanism that controls the growth of the secondary vortices, and scale-resolving computational fluid dynamics (CFD) allowed to dive deep into the details of the vorticity generation. Along these lines, this paper discusses the end-wall flow characteristics of the T106 LPT profile at Re = 120 K and M = 0.59 by benchmarking with experiments and investigating the impact of the incoming boundary layer state. The simulations are carried out with proven Reynolds-averaged Navier–Stokes (RANS) and large-eddy simulation (LES) solvers to determine if Reynolds-averaged models can capture the relevant flow details with enough accuracy to drive the design of this flow region. Part I of the paper focuses on the critical grid needs to ensure accurate LES and on the analysis of the overall time-averaged flow field and comparison between RANS, LES, and measurements when available. In particular, the growth of secondary flow features, the trace and strength of the secondary vortex system, and its impact on the blade load variation along the span and end-wall flow visualizations are analyzed. The ability of LES and RANS to accurately predict the secondary flows is discussed together with the implications this has on design.

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