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Direct numerical simulations (DNSs) were performed for flow near the wall surface with a distributed micro roughness (DMR) arrangement with various roughness densities. The Reynolds number was set to \(Re = 3,535\) based on the laminar boundary-layer thickness at the inlet boundary ( \(\delta _{s}\) ), with reference to the previous study (Hamada, Yakeno, and Obayashi, IJHFF, Vol. 104, 2023). The lengths of the computational domain in the streamwise and spanwise directions are \(L_{x}/\delta _{s} = 56.5\) and \(L_{y}/\delta _{s} = 11.3\) , respectively. An artificial disturbance was added at the inlet boundary to induce Tollmien-Schlichting (T-S) waves. The results of DNSs show that the DMR with the appropriate roughness density achieves a skin friction coefficient ( \(C_{f}\) ) reduction in comparison with the smooth flat plate case. The gradual collapse of the large-scale vortex structure suppresses the abrupt fluctuation in the \(C_{f}\) and increase in turbulent kinetic energy, thus achieving the \(C_{f}\) reduction.

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DNS Study of Flow Mechanism Contributing to Drag Reduction Over Distributed Micro Roughness

  • 会议论文

  • 发表日期：

    2026年

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  • Takuto Ogawa,
  • Aiko Yakeno

摘要

Direct numerical simulations (DNSs) were performed for flow near the wall surface with a distributed micro roughness (DMR) arrangement with various roughness densities. The Reynolds number was set to \(Re = 3,535\) based on the laminar boundary-layer thickness at the inlet boundary ( \(\delta _{s}\) ), with reference to the previous study (Hamada, Yakeno, and Obayashi, IJHFF, Vol. 104, 2023). The lengths of the computational domain in the streamwise and spanwise directions are \(L_{x}/\delta _{s} = 56.5\) and \(L_{y}/\delta _{s} = 11.3\) , respectively. An artificial disturbance was added at the inlet boundary to induce Tollmien-Schlichting (T-S) waves. The results of DNSs show that the DMR with the appropriate roughness density achieves a skin friction coefficient ( \(C_{f}\) ) reduction in comparison with the smooth flat plate case. The gradual collapse of the large-scale vortex structure suppresses the abrupt fluctuation in the \(C_{f}\) and increase in turbulent kinetic energy, thus achieving the \(C_{f}\) reduction.