A priori evaluation of dynamic subgrid models of turbulence in square ductflow

A priori tests of two dynamic subgrid-scale (SGS) turbulence models have be en performed using a highly resolved direct numerical simulation database f or the case of turbulent incompressible flow in a straight duct of square c ross-section. The model testing is applied only to the homogeneous flow dir ection where grid filtering can be applied without the introduction of comm utation errors. The first SGS model is the dynamic (Smagorinsky/eddy viscos ity) SGS model (DSM) developed by Germano et al. [1] while the second is th e dynamic two parameter (mixed) model (DTM) developed by Salvetti and Baner jee [2]. For the Smagorinsky model we have used both the Fourier cut-off fi lter and a modified Gaussian filter which has the property that it removes aliasing errors in consistent a priori model-testing for spectral-based dat asets. Results largely consistent with those found for plane channel flow a re observed but with some slight differences in the corner regions. As foun d in prior studies of this sort, there is a very poor correlation of the mo delled and exact subgrid-scale dissipation in the case of the DSM. The DSM over-predicts subgrid-scale dissipation on average. Instantaneously, the mo del provides an inaccurate representation of subgrid-scale dissipation, in general underestimating the magnitude by approximately one order of magnitu de. On the other hand, the DTM shows excellent agreement with the exact SGS dissipation over most of the duct cross-section with a correlation coeffic ient of approximately 0.9.