Abstract
The flow of a viscous fluid in a plane channel is simulated numerically following the DNS approach, and using a computational code for the numerical integration of the Navier-Stokes equations implemented on a hybrid CPU/GPU computing architecture (for the meaning of symbols and acronyms used, one can refer to the Nomenclature). Three turbulent-flow databases, each representing the turbulent statistically-steady state of the flow at three different values of the Reynolds number, are built up, and a number of statistical moments of the fluctuating velocity field are computed. For turbulent-flow-structure investigation, the vortex-detection technique of the imaginary part of the complex eigenvalue pair in the velocity-gradient tensor is applied to the fluctuating-velocity fields. As a result, and among other types, hairpin vortical structures are unveiled. The processes of evolution that characterize the hairpin vortices in the near-wall region of the turbulent channel are investigated, in particular at one of the three Reynolds numbers tested, with specific attention given to the relationship that exists between the dynamics of the vortical structures and the occurrence of ejection and sweep quadrant events. Interestingly, it is found that the latter events play a preminent role in the way in which the morphological evolution of a hairpin vortex develops over time, as related in particular to the establishment of symmetric and persistent hairpins. The present results have been obtained from a database that incorporates genuine DNS solutions of the Navier-Stokes equations, without superposition of any synthetic structures in the form of initial and/or boundary conditions for the simulations.
Highlights
Isosurface representation representation of of vortical vortical structures structures in in conjunction conjunction with with quadrant quadrant isosurface ci isosurface representation of vortical structures in conjunction with quadrant events at t 450: vortical
(isosurfaces of ejections are shown in red, isosurfaces of sweeps are shown at t “events: t in events at t 220: (a) vortical structures are shown in cyan; (b) vortical structures are colored with the values yellow): (a) vortical structures are shown in cyan; (b) vortical structures are colored with the values vortical structures are shown in cyan; (b) vortical structures are colored with the values of λ: (a) vortical structures are shown in cyan; (b) vortical structures are colored with the values
Numerical Simulation (DNS) of the turbulent flow of incompressible fluid in a plane channel been executedSimulation at three values of of thethe friction-velocity number, fluid usinginaahybrid turbulent flowReynolds of incompressible plane computing architecture, and an analysis has been performed of the characteristics of the channel has been executed at three values of the friction-velocity Reynolds number, using a hybrid vortical structures in the wall region of an theanalysis turbulent flow
Summary
The flow of a viscous fluid in a channel has been investigated numerically by several authors in the recent past, becoming a reference case for the study of wall turbulence with DNS. The aim of these simulations is mainly that of calculating a given number of time steps of the statistically-steady turbulent flow in the channel, to build up DNS databases, and extracting from the latter useful information for a better comprehension of the wall-turbulence phenomena.
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