Large Eddy Simulation of Wake Formation around a Free Surface–Piercing Circular Cylinder

2020 ◽  
Vol 37 (1) ◽  
Author(s):  
Hang Guo ◽  
Fahim Bahrian ◽  
Weipeng Zhang ◽  
Cong Sun ◽  
Jian Hu
Keyword(s):  
Free Surface ◽  
Circular Cylinder ◽  
Large Eddy Simulation ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Wake Formation

Large Eddy Simulation of a Flow Past a Free Surface Piercing Circular Cylinder

2001 ◽  
Vol 124 (1) ◽  
pp. 91-101 ◽  
Author(s):  
T. Kawamura ◽  
S. Mayer ◽  
A. Garapon ◽  
L. Sørensen
Keyword(s):  
Free Surface ◽  
Surface Wave ◽  
Circular Cylinder ◽  
Large Eddy Simulation ◽  
Vortex Shedding ◽  
Shear Layers ◽  
Computational Results ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Good Agreement

Interactions between surface waves and underlying viscous wake are investigated for a turbulent flow past a free surface piercing circular cylinder at Reynolds number Re=2.7×104 using large eddy simulation (LES). The computations have been performed for three Froude numbers Fr=0.2, 0.5 and 0.8 in order to examine the influence of the Froude number. A second-order finite volume method coupled with a fractional step method is used for solving the grid-filtered incompressible Navier-Stokes equations. The computational results are found to be in good agreement with the available experimental data. At low Froude numbers Fr=0.2 and 0.5, the amplitude of generated surface wave is small and the influence on the wake is not evident. On the other hand, strong wave-wake interactions are present at Fr=0.8, when the generated free surface wave is very steep. It is shown that structures of the underlying vortical flow correlate closely with the configuration of the free surface. Computational results show presence of a recirculation zone starting at the point where the surface slope changes discontinuously. Above this zone the surface elevation fluctuates intensively. The computed intensity of the surface fluctuation is in good agreement with the measurements. It is also shown that the periodic vortex shedding is attenuated near the free surface at a high Froude number. The region in which the periodic vortex shedding is hampered extends to about one diameter from the mean water level. It is qualitatively shown that the separated shear layers are inclined outward near the free surface due to the generation of the surface waves. This change in the relation between two shear layers is suggested to be responsible for the attenuation of the periodic vortex shedding.

Large-eddy simulation of free-surface decaying turbulence with dynamic subgrid-scale models

1997 ◽  
Vol 9 (8) ◽  
pp. 2405-2419 ◽  
Author(s):  
M. V. Salvetti ◽  
Y. Zang ◽  
R. L. Street ◽  
S. Banerjee
Keyword(s):  
Free Surface ◽  
Large Eddy Simulation ◽  
Subgrid Scale ◽  
Eddy Simulation ◽  
Scale Models ◽  
Large Eddy ◽  
Decaying Turbulence

Large-eddy simulation of free-surface turbulence

2001 ◽  
Vol 440 ◽  
pp. 75-116 ◽  
Author(s):  
LIAN SHEN ◽  
DICK K. P. YUE
Keyword(s):  
Boundary Condition ◽  
Free Surface ◽  
Large Eddy Simulation ◽  
Surface Boundary ◽  
Eddy Simulation ◽  
Large Eddy ◽  
Similarity Model ◽  
Scale Similarity ◽  
Surface Turbulence ◽  
Free Surface Turbulence

In this paper we investigate the large-eddy simulation (LES) of the interaction between a turbulent shear flow and a free surface at low Froude numbers. The benchmark flow field is first solved by using direct numerical simulations (DNS) of the Navier–Stokes equations at fine (1282 × 192 grid) resolution, while the LES is performed at coarse resolution. Analysis of the ensemble of 25 DNS datasets shows that the amount of energy transferred from the grid scales to the subgrid scales (SGS) reduces significantly as the free surface is approached. This is a result of energy backscatter associated with the fluid vertical motions. Conditional averaging reveals that the energy backscatter occurs at the splat regions of coherent hairpin vortex structures as they connect to the free surface. The free-surface region is highly anisotropic at all length scales while the energy backscatter is carried out by the horizontal components of the SGS stress only. The physical insights obtained here are essential to the efficacious SGS modelling of LES for free-surface turbulence. In the LES, the SGS contribution to the Dirichlet pressure free-surface boundary condition is modelled with a dynamic form of the Yoshizawa (1986) expression, while the SGS flux that appears in the kinematic boundary condition is modelled by a dynamic scale-similarity model. For the SGS stress, we first examine the existing dynamic Smagorinsky model (DSM), which is found to capture the free-surface turbulence structure only roughly. Based on the special physics of free-surface turbulence, we propose two new SGS models: a dynamic free-surface function model (DFFM) and a dynamic anisotropic selective model (DASM). The DFFM correctly represents the reduction of the Smagorinsky coefficient near the surface and is found to capture the surface layer more accurately. The DASM takes into account both the anisotropy nature of free-surface turbulence and the dependence of energy backscatter on specific coherent vorticity mechanisms, and is found to produce substantially better surface signature statistics. Finally, we show that the combination of the new DFFM and DASM with a dynamic scale-similarity model further improves the results.

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