Large-scale Secondary Vortices Generated by Wall
Actuations: Application to the Turbulent Channel Flow

Ni, Weidan; Fang, Jian; Moulinec, Charles; Emerson, David R.; Lu, Lipeng; Yao, Yufeng

Abstract

The large-scale streamwise vortex (LSSV) generation mechanism in the turbulent boundary layer is closely linked to the turbulent mixing process and its potential to suppress flow separation. Direct numerical simulations (DNSs) of weakly compressible (Ma = 0.2) turbulent channel
ow using Spanwise Alternatively Distributed Strips (SADS) Control are conducted to investigate the characteristics of LSSV induced by small-scale wall actuation. The compressible
DNS code ASTR is used as a solver and the mesh dimension is 392 x 192 x 256 for a channel of 2pi x 2 x 2pi size. The DNS of the unperturbed case is first validated against the incompressible DNS data of Moser et al. SADS are
then obtained by applying out-of-phase control (OPC) and in-phase control (IPC), as presented in Figure 1 (a). The turbulent coherent structures in the channel using SADS are alternatively enhanced and suppressed by SADS,
as presented in Figure 1 (b). Instantaneous and mean velocity fields, shown in Figure 2, present large-scale modes in the y-z plane. Large-scale low-speed regions are identified above the OPC strips and when observing the mean velocity field, the low-speed region exhibits a steady flow streak structure. Near-wall
velocities increase above the IPC region because turbulence is enhanced there. Turbulent kinetic energy (TKE) and Reynolds shear stress (RSS) both increasein the near-wall region above the IPC strips. This is attributed to the activated near-wall turbulence generated by IPC. However, in the region above the OPC strips, large-scale clusters are present, with higher values of TKE and RSS in the outer part of the channel, although the turbulence coherent structures in the near-wall region are supressed by OPC. Therefore, the LSSVs generated by the current small-scale wall actuation present a strong ability in enhancing momentum transport and mixing. All the simulations are conducted on the UK national facility ARCHER using 2,400 cores.

• Presentation Conference Type: Conference Paper (unpublished)
• Conference Name: Parallel CFD Conference 2017
• Start Date: May 15, 2017
• End Date: May 17, 2017
• Acceptance Date: May 15, 2017
• Publication Date: May 17, 2017
• Peer Reviewed: Peer Reviewed
• Public URL: https://uwe-repository.worktribe.com/output/1434971
• Additional Information: Title of Conference or Conference Proceedings : Parallel CFD Conference 2017