Preliminary Study of the SGS Time Scales for Compressible Boundary Layers using DNS Data

We use direct numerical simulation data of turbulent boundary layers and a priori testingto estimate the time scales that are associated with the subgrid-scale terms in the conser-
vative form of the governing equations. The exact and modeled subgrid-scale terms are
gathered from the filtered direct numerical simulation fields for several time steps. The
model coefficients are evaluated using the Lagrangian averaging technique. We analyze the
time scales directly by performing temporal autocorrelations along fluid particle paths. To
assess the subgrid-scale models, we compare the time scales and the quantities given by the
exact and modeled representations. It is found that in general, mixed models give a larger
integral time scale than that of the exact terms and that the discrepancy is not related to
the prescribed memory length associated with the evaluation of the model coefficients.