scholarly journals Large-eddy simulation of wave-breaking induced turbulent coherent structures and suspended sediment transport on a barred beach

2017 ◽  
Vol 122 (1) ◽  
pp. 207-235 ◽  
Author(s):  
Zheyu Zhou ◽  
Tian-Jian Hsu ◽  
Daniel Cox ◽  
Xiaofeng Liu
Keyword(s):  
Sediment Transport ◽  
Large Eddy Simulation ◽  
Suspended Sediment ◽  
Coherent Structures ◽  
Wave Breaking ◽  
Suspended Sediment Transport ◽  
Eddy Simulation ◽  
Turbulent Coherent Structures ◽  
Large Eddy

scholarly journals LARGE-EDDY SIMULATION OF OSCILLATORY FLOW AND MORPHODYNAMICS OVER RIPPLES

2017 ◽  
pp. 23
Author(s):  
Georgios Leftheriotis ◽  
Athanassios Dimas
Keyword(s):  
Sediment Transport ◽  
Large Eddy Simulation ◽  
Oscillatory Flow ◽  
Three Dimensional ◽  
Immersed Boundary ◽  
Suspended Sediment Transport ◽  
Mean Flow ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Bed Form

The objective of the present study was to study the morphodynamical development of ripples in a movable bed. The methodology is based on the coupling of fluid flow, sediment transport and morphodynamics. A well-resolved large-eddy simulation (LES) is employed for the simulation of the three-dimensional turbulent oscillatory flow and the corresponding bed and suspended sediment transport over a rippled bed. The evolution of the bed form is obtained by the numerical solution of the Exner equation based on the spanwise-mean flow and sediment transport conditions. The Immersed Boundary method is implemented for the imposition of fluid and sediment boundary conditions on the moving bed surface. Results are presented for ripple creation and propagation from a quasi-flat bed, as well as results of initially sinusoidal ripples adapting to water conditions, based on the mobility number, ψ. The numerical model demonstrates phenomena of ripple creation, propagation and migration, resulting in ripple lengths in agreement with those predicted by empirical equations. It was shown that under the same hydrodynamic forcing, the bed tends to reach the same equilibrium state, regardless of the initial bed form.

Large Eddy Simulation of Coherent Structures over Forest Canopy

2010 ◽  
pp. 143-149 ◽  
Author(s):  
K. Gavrilov ◽  
G. Accary ◽  
D. Morvan ◽  
D. Lyubimov ◽  
O. Bessonov ◽  
...  
Keyword(s):  
Large Eddy Simulation ◽  
Coherent Structures ◽  
Forest Canopy ◽  
Eddy Simulation ◽  
Large Eddy

Large-Eddy Simulation of Unsteady Surface Pressure Over a LP Turbine Blade Due to Interactions of Passing Wakes and Inflexional Boundary Layer

2005 ◽  
Author(s):  
S. Sarkar ◽  
Peter R. Voke
Keyword(s):  
Large Eddy Simulation ◽  
Turbine Blade ◽  
Coherent Structures ◽  
Pressure Fluctuations ◽  
Time Dependent ◽  
Suction Surface ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Grid Points ◽  
Lp Turbine

The unsteady pressure over the suction surface of a modern low-pressure (LP) turbine blade subjected to periodically passing wakes from a moving bar wake generator is described. The results presented are a part of detailed Large-Eddy Simulation (LES) following earlier experiments over the T106 profile for a Reynolds number of 1.6×105 (based on the chord and exit velocity) and the cascade pitch to chord ratio of 0.8. The present LES uses coupled simulations of cylinder for wake, providing four-dimensional inflow conditions for successor simulations of wake interactions with the blade. The three-dimensional, time-dependent, incompressible Navier-Stokes equations in fully covariant form are solved with 2.4×106 grid points for the cascade and 3.05×106 grid points for the cylinder using a symmetry-preserving finite difference scheme of second-order spatial and temporal accuracy. A separation bubble on the suction surface of the blade was found to form under the steady state condition. Pressure fluctuations of large amplitude appear on the suction surface as the wake passes over the separation region. Enhanced receptivity of perturbations associated with the inflexional velocity profile is the cause of instability and coherent vortices appear over the rear half of the suction surface by the rollup of shear layer via Kelvin-Helmholtz (K-H) mechanism. Once these vortices are formed, the steady-flow separation changes remarkably. These coherent structures embedded in the boundary amplify before breakdown while traveling downstream with a convective speed of about 37 percent of the local free-stream speed. The vortices play an important role in the generation of turbulence and thus to decide the transitional length, which becomes time-dependent. The source of the pressure fluctuations on the rear part of the suction surface is also identified as the formation of these coherent structures. When compared with experiments, it reveals that LES is worth pursuing as an understanding of the eddy motions and interactions is of vital importance for the problem.

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