Bursts in turbulent channel flows and the interaction between flow structures of multiple scales

In the logarithmic region of turbulent channel flows, strong bursts of the wall-normal velocity, v, are known to play a crucial role in the production of turbulent kinetic energy (TKE). In turbulent channel flows, the only possible mechanism by which the wall-normal velocity can gain kinetic energy (v²) is via the work of pressure (i.e. continuity) as represented by ⟨pdv/dy⟩ term in the TKE budget equations. Therefore, events of strong pdv/dy are used as a proxy for strong bursts of v. When the wall-normal locations of strong pressure source and burst are close, the underlying flow pattern is the backward leaning v structures as previously observed (Jimenez, Phys. Fluids 2013). However, when the wall-normal locations of strong pressure source and burst are far apart, bursts are associated with a certain alignment of flow structures of different sizes, revealing a mechanism in which the interaction between structures of multiple scales can lead to strong bursts in the log region of turbulent channel flows.