A dynamic two-equation sub grid scale model

In this paper we demonstrate that the transport equation of the generalised subgrid scale (SGS) turbulent stress tensor is form-invariant but not frame-indifferent under Euclidean transformations of the frame. A new closure equation between the generalized SGS turbulent stress tensor and the resolved kinematic quantities is proposed. The closure equation at the basis of the proposed model (Two-Equation Model, TEM): a) respects the principle of the turbulence frame indifference [ 1]; b) takes into account both the anisotropy of the turbulence velocity scales and turbulence length scales; c) removes any balance assumption between the production and dissipation of SGS turbulent kinetic energy; d) assumes scale similarity in the definition of the second-order tensor representing the turbulent velocity scales. In the proposed model: a) the closure coefficient C which appears in the constitutive equation is uniquely determined without using Germano's dynamic procedure [ 2]; b) 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; c) the viscous dissipation e of the generalized SGS turbulent kinetic energy is calculated by solving the e balance equation. The proposed model is tested for a turbulent channel flow at Reynolds numbers ( based on friction velocity and channel half-width) ranging from 180 to 2340.