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On the Euler rotation angle and axis of a subgrid-scale stress model

In this research, geometrical characteristics of the constitutive relation between the subgrid-scale (SGS) stress and filtered strain rate tensors are investigated based on the concept of Euler rotation angle and axis. Four different SGS stress models are studied using a priori tests by processing a comprehensive direct numerical simulation (DNS) data set of a zero-pressure-gradient transitional boundary-layer flow. The proposed approach is proven to be effective for demonstrating geometrical properties of a SGS stress model and for quantifying its degree of nonlinearity.