DNS Study of Drag Reduction Effect on Ultra-Fine Rough Surfaces

POSTER

Abstract

The ultra-fine rough surfaces, even if it is randomly-distributed in space, sometimes delay transition and reduce drag, when their size is within the viscous sublayer (Tani (1988), Oguri et al. (1996), Tameike et al. (2021) and Hamada et al. (2022)). We name that surface structure to reduce drag as Distributed Micro Roughness (DMR). We demonstrated direct numerical simulation of Tollmien–Schlichting (T-S) transitional flow over the sand-grind roughness surface, that was implemented in the real shape we used in the wind tunnel experiment. Firstly, we confirmed the drag reduction effect over the sand-grid rough surface, by observation of the turbulent kinetic energy (TKE) distribution and friction drag with calculation of the integral value of the averaged Reynolds shear stress. Secondary, we analyzed the mechanism of the statistic change, by applying the statistical decomposition of temporal phase-averaging of the TS wave and other three-dimensional components. The results show that the TS vortex tends to break down into turbulence over the sand-grind rough surface, although TKE and friction drag were suppressed compared to the smooth surface. In the presentation, we will discuss the mechanism more in detail.

*Simulations were performed on the Supercomputer system at the Institute of Fluid Science (IFS) in Tohoku University. We acknowledge NEDO and the Collaborative Research Project Fund of IFS.

Publication: Hamada, S., Yakeno, A., Obayashi, S. & Nugroho, B., Small wavy roughness effect on T-S wave and three-dimensional transition by Direct Numerical Simulation, 73rd Annual Meeting of the APS Division of Fluid Dynamics (2020).

Hamada, S., Yakeno, A., & Obayashi, S., Ultra-Fine Roughness Effect on Transition Delay Using Direct Numerical Simulation, 12th International Symposium on Turbulence and Shear Flow Phenomena (2022).

Hamada, S., Yakeno, A., Obayashi, S. & Nugroho, B., Ultra-fine surface roughness effect on boundary layer transition, 17th International Conference on Flow Dynamics (2020).

Hamada, S., Yakeno, A., Obayashi, S. & Nugroho, B., Transition delay and drag reduction mechanism by designed surface roughness, 18th International Conference on Flow Dynamics (2021).

Tameike, H., Yakeno, A. & Obayashi, S. 2021 Influence of small wavy roughness on flatplate boundary layer natural transition, Journal of Fluid Science and Technology 16 (1), JFST0008–JFST0008.

Presenters

  • Shingo Hamada

    • Tohoku University

Authors

  • Shingo Hamada

    • Tohoku University

  • AIKO YAKENO

    • Tohoku University

  • Shigeru Obayashi

    • Tohoku University
    • Institute of Fluid Science, Tohoku University