Large-Scale Structure and the Sustenance Mechanism in Turbulent Poiseuille Flow at Low Reynolds Number(Fluids Engineering)

Abstract

The direct numerical simulation (DNS) with a spectral method is performed to study the large-scale structure in relaminarizing channel flow at low Reynolds number. The flow structure coined as turbulent-laminar pattern simultaneously contains the quasi-laminar and turbulent regions, outlines of which are maintained over time. In the quasi-laminar region, streamwise vortical structure almost disappears though weak streamwise vorticity is arrayed regularly around the channel center. Moreover, very long streak structure appears in the quasi-laminar region. In the turbulent region, however, many quasi-streamwise vortices are clustered around the curved streak structure. The criterion is defined to quantitatively distinguish these regions by using streamwise vorticity, and the turbulent energy budget is calculated over each region. As a result, it is found that quasi-laminar and turbulent regions simultaneously interact with each other; in the region away from the wall, there is the inrush of high-speed fluid toward the turbulent region, while in the near-wall region, low- and high-speed streaks are swept to quasi-laminar region. It is also found that the turbulent-laminar pattern is sustained by the energy transfer between two regions and the generation of the flow along the turbulent region.