A STRAIN PARAMETER TURBULENCE MODEL AND ITS APPLICATION TO HOMOGENEOUS AND THIN SHEAR FLOWS

The present paper examines the basic tenets upon which widely-used two -equation (k-epsilon) turbulence models are based. It is argued that t here exists a weakness at the core of this group of models, namely in the assumed stress/rate-of-strain constitutive equation. These remarks apply to both the 'high-Reynolds-number' parent model and to 'low-Rey nolds-number' variants of the formulation. Dimensional considerations and the work of Lee et al. (Proceedings of the Sixth Symposium on Turb ulent Shear Flows, 1987; J. Fluid Mech. 216 (1990) 561-583) support th e contention that the constitutive relation should take account of the ratio of turbulence Co mean strain timescales. In an extension of thi s approach, following Townsend (J. Fluid Mech. 41 (1970) 13-46) and Ma xey (J. Fluid Mech. 124 (1982) 261-282), the concept of effective tota l strain is introduced. A 'strain parameter', S, is then defined as th e subject of a third transport equation and a new turbulence model dam ping function is made to depend principally upon S. The model is compa red with data for homogeneous flow transients, steady fully-developed channel flow, and mixed convection flows. (C) 1998 Elsevier Science In c. All rights reserved.