EXPANDING THE LIMITS OF EQUILIBRIUM 2ND-MOMENT TURBULENCE CLOSURES

The paper discusses possibilities for refinements of conventional ''eq uilibrium'' second-moment turbulence closure models, aimed at improvin g model performances in predicting turbulent flows of greater complexi ty. In focus are the invariant modelling of the low-Re-number and wall proximity effects, as well as extra strain-rates and control of the t urbulence length-scale. In addition to satisfying most of the basic ph ysical constraints, the main criterion for model validation was the qu ality of reproduction of flow and turbulence details, particularly, in the vicinity of a solid wall, in a broad variety of non-equilibrium f lows featured by different phenomena. It is demonstrated that the new model, which includes several new modifications, but also some propose d in the past, can satisfactorily reproduce a range of attached and se parating flows with strong time- or space-variations or abrupt changes of boundary conditions. Cases considered cover a wide range of Re-num bers involving in some cases also the laminar-to-turbulent or reverse transition.