Rotational vector-based analysis of turbulent structures in channel flow using large eddy simulation simulation

Abstract

Even with modern measurement techniques and data from direct numerical simulation (DNS), it is very difficult to identify the individual attached eddies and understand their dynamical behavior due to the multi-scale nature of the eddies in wall-bounded flows, which puts these issues at the center of the current debate. However, Liutex vector ( L for short), a rotational vector field with information on both the rotation axis and swirling strength, has recently been developed by Prof. Liu’s group as a more accurate and clear definition of a vortex. Combining conventional and L methods may provide more detailed information about the complex flow structures as well as insights into the flow’s mixing and transport features. We simulated the channel flow in large eddy simulation by implementing an inflow condition based on the box turbulence. After validating the results with DNS data, we used L isosurfaces and their vector profiles to track ordered flow structures in wall-bounded turbulence. Based on the data, we observe numerous turbulent phenomena that have been described in other works with different visualization techniques. Moreover, the shear contamination on the wall is the most severe while all the root-mean-square L component variations are negligible. Due to the presence of background shear, the peak location of vorticity fluctuation is closer to the wall than the corresponding L fluctuation, and the displacement of peak location brought on by shear contamination is greatest for the spanwise component (z-component) of the vorticity fluctuation. According to the two-point correlation of L components, the streamwise size of turbulent structures does not vary considerably with y+ , however, the spanwise size of turbulent structures increases gradually as y+ increases.