Nonlinear Interaction of Coherent Structures in Wall Turbulence at Low-to-Moderate Reynolds Numbers

Abstract

Direct numerical simulation of turbulent channel flow at Re _τ = 110 ∼ 650 is made in order to examine the nonlinear interaction of coherent structures in wall turbulence through the Karhunen-Loève decomposition of turbulent fluctuations. When Re _τ = 110, the nonlinear interaction acts as sink for the turbulence energy of vortical structures at y ⁺ ∼ 20, which correspond to the near-wall streamwise vortices. The energy is transferred toward/away from y ⁺ ∼ 20. On the other hand, when the Reynolds number increases, the streamwise vortices gains energy through the nonlinear interaction from the vortical structures at 20 < y ⁺ < 100. It is also found that direct interaction between inner (y ⁺ < 100) and outer (y ⁺ > 100) layers has minor effect on near-wall dynamics even at Re _τ = 650.