1,721,030 research outputs found
Form Invariance and Frame Indifference of Closure Relations in LES
No full textIn this paper the principle of Turbulent Frame Indifference is revised. It is demonstrated that not all the turbulent closure relations in LES must fulfil the principle of Turbulent Frame Indifference: in the turbulent closure relations, the modelled expressions of an unknown objective tensor must be formulated in terms of objective tensors (allowing the closure relations to fulfil the requirement of form invariance) and must retain the same dependence (on the angular velocity of the frame) of the unknown tensor. It is demonstrated that, since the generalized SGS turbulent stress tensor is objective and frame independent, closure relations for this tensor must fulfil the principle of Turbulent Frame Indifference. A new closure relation for the generalized SGS turbulent stress tensor is proposed. The proposed closure relation complies with the principle of Turbulent Frame Indifference. In the proposed model the generalized SGS turbulent stress tensor is related exclusively to the generalized SGS turbulent kinetic energy (which is calculated by means of its balance equation) and the modified Leonard tensor. The viscous dissipation of the generalized SGS turbulent kinetic energy is calculated by solving the balance equation of . It is demonstrated that the balance equation of the viscous dissipation is form-invariant but frame-dependent under Euclidean transformations of the frame; the closure relations proposed in this paper allow the modeled balance equation of to respect the properties of form-invariance and frame-dependence of the exact equation
Simulation of wave run-up by means of the exact solution of the wet/dry Riemann problem
Full text linkAn innovative method for the simulation of the hydrodynamics in the swash zone, related to the
wave run-up phenomenon, is presented. This method applies the exact solution of the Riemann problem over
a dry bed to correctly evaluate the celerity of water waves propagating over the shore, and so to precisely track
the coastline location. The simulations of velocity and wave fields outside the surf zone, inside the surf zone
and in the swash zone, are carried out by means of a numerical model which solves 3D motion equations
expressed in integral form, with a vertical coordinate that varies in time in order to follow the free surface
evolution. Several numerical validation tests are carried out, in order to verify the capability of the method to
track the coastline
Noll’s axioms and formulation of the closure relations for the subgrid turbulent tensor in large eddy simulation
Full text link-In this paper, the relation between the Noll formulation of the principle of material frame indifference and the principle of turbulent frame indifference in large eddy simulation, is revised. The principle of material frame indifference and the principle of turbulent frame indifference proposed by Hutter and Joenk imposes that both constitutive equations and turbulent closure relations must respect both the requirement of form invariance, and the requirement of frame independence. In this paper, a new rule for the formalization of turbulent closure relations, is proposed. The generalized SGS turbulent stress tensor is related exclusively to the generalized SGS turbulent kinetic energy, which is calculated by means of its balance equation, and the modified Leonard tensor
DYNAMIC BEHAVIOUR OF PRIMARY PRODUCERS IN SHALLOW MARINE WATER DUE TO NUTRIENT ENRICHMENT
No full textA New Turbulence Model for Large Eddy Simulation
No full textThe present - day Large Eddy Simulation models based on the Smagorinsky assumption and the drawbacks of the dynamic calculation of the closure coefficient for the generalised subgrid scale turbulent stress tensor are presented. The relations between numerical scheme conservation property of mass, momentum and kinetic energy and the
drawbacks of the dynamic Smagorinsky - type turbulence models are shown. A new turbulence model is proposed. The proposed model:
a) is able to take into account the anisotropy of the turbulence;
b) remove any balance assumption between the production and dissipation of sub grid scale turbulent kinetic energy;
c) is able to eliminate the numerical effects produced by the non conservation a priori of the resolved kinetic energy.
New closure relations for the unknown terms of the subgrid scale viscous dissipation balance equation are proposed. The filtered momentum equations are solved by using a sixth order finite difference scheme. The proposed model is tested for a turbulent channel flow at Reynolds numbers (based on friction velocity and channel half-width) ranging from 395 to 234
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