Evaluation of LES models for flow over bluff body from engineering application perspective
01 Feb 2005-Sadhana-academy Proceedings in Engineering Sciences (Springer India)-Vol. 30, Iss: 1, pp 11-20
TL;DR: In this article, three SGS stress closure LES models are evaluated for turbulent flow over a square cylinder and it is concluded that a one-equation model for subgrid kinetic energy is the best choice.
Abstract: Three SGS stress closure LES models are evaluated for turbulent flow over a square cylinder. Emphasis is placed on solving engineering-application-type problems on affordable computer resources and within reasonable turnaround times. Results are compared with available experimental data and previously published workshop results. Numerical strategies are kept the same for all the cases. Results are also discussed keeping in view limitations of LES methodology of modelling for practical problems and current developments. It is concluded that a one-equation model for subgrid kinetic energy is the best choice.
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13 Jul 2018
TL;DR: In this article, a simulation study of wind loading on a group of octagonal cylinders with various longitudinal spacing is presented, where the surface static pressures at different locations of the cylinders were predicted for different longitudinal spacing with the help of computational program in terms hydraulic diameter (D) of the cylinder across flow direction ranging from one to eight times.
Abstract: A simulation study of wind loading on a group of octagonal cylinders with various longitudinal spacing is presented here. This simulation was carried out arranging two cylinders with same hydraulic diameter, placing one in upstream and one in downstream at uniform flow velocity 13.2 m/s using ANSYS 16. The surface static pressures at different locations of the cylinders were predicted for different longitudinal spacing with the help of computational program in terms hydraulic diameter (D) of the cylinder across flow direction ranging from one to eight times. Pressure coefficients were calculated from the static pressure distributions. It was observed that the drag coefficients are considerably smaller compared to those for a sharp-edged square cylinder and wind loading on a single structure is more severe than when it is a part of a group. The findings confirm the previous experimental works in similar arrangement of a group of octagonal cylinders.
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TL;DR: In this article, an extended period numerical integration of a baroclinic primitive equation model has been made for the simulation and the study of the dynamics of the atmosphere's general circulation, and the solution corresponding to external gravitational propagation is filtered by requiring the vertically integrated divergence to vanish identically.
Abstract: An extended period numerical integration of a baroclinic primitive equation model has been made for the simulation and the study of the dynamics of the atmosphere's general circulation. The solution corresponding to external gravitational propagation is filtered by requiring the vertically integrated divergence to vanish identically. The vertical structure permits as dependent variables the horizontal wind at two internal levels and a single temperature, with the static stability entering as a parameter. The incoming radiation is a function of latitude only corresponding to the annual mean, and the outgoing radiation is taken to be a function of the local temperature. With the requirement for thermal equilibrium, the domain mean temperature is specified as a parameter. The role of condensation is taken into account only as it effectively reduces the static stability. All other external sources and sinks of heat are assumed to balance each other locally, and are thus omitted. The kinematics are th...
12,952 citations
"Evaluation of LES models for flow o..." refers background in this paper
...Ever since Smagorinsky (1963) proposed first model 1 for the SGS stresses, many newer models have been developed....
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...2.1 Conventional smagorinsky model Smagorinsky (1963) proposed the first subgrid-scale stress model....
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...Ever since Smagorinsky (1963) proposed the first model for the SGS stresses, many newer models have been developed....
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... Smagorinsky (1963) proposed the first subgrid-scale stress model....
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06 Jan 1992
8,784 citations
TL;DR: In this article, a new eddy viscosity model is presented which alleviates many of the drawbacks of the existing subgrid-scale stress models, such as the inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes.
Abstract: One major drawback of the eddy viscosity subgrid‐scale stress models used in large‐eddy simulations is their inability to represent correctly with a single universal constant different turbulent fields in rotating or sheared flows, near solid walls, or in transitional regimes. In the present work a new eddy viscosity model is presented which alleviates many of these drawbacks. The model coefficient is computed dynamically as the calculation progresses rather than input a priori. The model is based on an algebraic identity between the subgrid‐scale stresses at two different filtered levels and the resolved turbulent stresses. The subgrid‐scale stresses obtained using the proposed model vanish in laminar flow and at a solid boundary, and have the correct asymptotic behavior in the near‐wall region of a turbulent boundary layer. The results of large‐eddy simulations of transitional and turbulent channel flow that use the proposed model are in good agreement with the direct simulation data.
6,747 citations
TL;DR: In this paper, the subgrid-scale closure method developed by Germano et al. is modified by use of a least squares technique to minimize the difference between the closure assumption and the resolved stresses.
Abstract: The subgrid‐scale closure method developed by Germano et al. is modified by use of a least squares technique to minimize the difference between the closure assumption and the resolved stresses. This modification removes a source of singularity and is believed to improve the method’s applicability.
3,730 citations
TL;DR: In this article, the three-dimensional, primitive equations of motion have been integrated numerically in time for the case of turbulent, plane Poiseuille flow at very large Reynolds numbers.
Abstract: The three-dimensional, primitive equations of motion have been integrated numerically in time for the case of turbulent, plane Poiseuille flow at very large Reynolds numbers. A total of 6720 uniform grid intervals were used, with sub-grid scale effects simulated with eddy coefficients proportional to the local velocity deformation. The agreement of calculated statistics against those measured by Laufer ranges from good to marginal. The eddy shapes are examined, and only the u-component, longitudinal eddies are found to be elongated in the downstream direction. However, the lateral v eddies have distinct downstream tilts. The turbulence energy balance is examined, including the separate effects of vertical diffusion of pressure and local kinetic energy.It is concluded that the numerical approach to the problem of turbulence at large Reynolds numbers is already profitable, with increased accuracy to be expected with modest increase of numerical resolution.
1,868 citations
"Evaluation of LES models for flow o..." refers background in this paper
...…study, numerical values of 0·13 and 0·094 have been set forCS andCk respectively to account appropriately for the energy in the resolvable turbulence (Deardorff 1970).1 is the filter width (grid size), and is the characteristic length scale of the largest subgrid-scale eddies and is taken to be…...
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