A Comparison of Structure and Dynamics Underlying Quasilinear and DNS Turbulence

A POD-based analysis was carried out on numerical data obtained from a DNS of a turbulent Poiseuille flow at Re=1650 and the corresponding quasilinear (QL) simulation. Striking similarity between the velocity fields of the streamwise mean roll-streak structure was seen in the two simulations. Compelling similarity was also seen between the perturbation velocity fields co-located with the streamwise mean roll-streak in the two simulations. This correspondence in the structure of the primary dynamical components underlying turbulence in QL and DNS suggests a similar dynamics is operating to maintain turbulence in these systems. Moreover, it is known that the QL system is a close approximation to a second order statistical state dynamics (SSD) formulation. This consideration invites exploiting the comprehensively characterized dynamics of turbulence in the second order SSD formulation to advance understanding of DNS turbulence. It is concluded that the SSP identified in the second order SSD, which is the same as that operating in QL turbulence, is also operating in DNS turbulence. This fundamental dynamical structure in the streamwise mean flow is identified as the roll-streak while the primary dynamical structure in the perturbation field is found to consist of a large cohort of decaying oblique waves.