Effects of strain-rate and subgrid dissipation rate on aligment trends between large and small scales in turbulent durt flow

摘要

HPIV measurements of a turbulent flow in a square duct are used for studying the 3-D geometric relations between SGS stresses, filtered strain rates and vorticity. Conditional sampling is perfomed based on the strian magnitude and SGS dissipation, including negative values. In regions of high dissipation, the flow is more likely to be in axisymmetric expansion with vorticity strongly aligned with the intermediate strain-rate eigendirection. The alighment between the most extensive SGS stress and the most compressive strain-rate (Tao et al 2000) vary with both the dissipation and strain-rate magnitude. The relative orientation pdf's of the other eigendirections of high dissipaton and strain-rate magnitude. However the alignments still differ from eddy viscosity models. The paper also presents the alignment pdf's between the measured stresses and model stresses by similarity SGS models. It is shown that the non-linear model (linearized similarity model) provides much better predictions of the alignment, a trend that presists in conditionally sampled data as well.