The interaction of vorticity and rate-of-strain in homogeneous sheared turbulence

Abstract

The coupled interaction of vorticity ω and rate-of-strain S in homogeneous sheared turbulence is investigated using direct numerical simulation. Conditional sampling and comparison with linear simulations reveal various aspects of the structure and dynamics. Due to the influence of the imposed ω and S, distinct directional features develop. Initial stretching of fluctuating ω by mean extensional strain and the presence of mean vorticity establish a predominant misalignment of ω with respect to the principal axes of S. The associated locally induced rotation of the S axes results in preferred orientations in ω and S. In high amplitude rotation-dominated regions of the flow, distinct characteristics are exhibited by the pressure Hessian Π due to the presence of small-scale spatial structure. Nonlocally induced S axes rotation through Π tends to counteract locally induced rotation in these regions. These features are absent in the linear flow which suggests a lack of spatial coherence in the corresponding intense ω2 regions. High amplitude strain-dominated and comparable rotation-strain regions are also considered. In general, the high amplitude conditional samples capture the main features of the flow. The underlying behavior of ω and S is essentially the same as in isotropic turbulence; the directional preferences observed in shear flow demonstrate the physical implications of the associated mechanisms. Although there is greater directional variation in flows with high Reλ/Sh, results indicate the significance of the persistence of mean shear.