Friction–pressure drag competition over turbulent flows with adaptive surface structures

Journal article, 2026

Surface geometry can significantly modify turbulence characteristics and thereby influence drag in turbulent boundary-layer flows. While compliant surfaces have shown promise for drag reduction, the hydrodynamic role of the deformation-induced surface geometry itself remains insufficiently understood. In the present study, a deformation-inspired surface profile previously obtained from a single flexible-wall unit is adopted as a prescribed geometry for rigid surface arrays, and the resulting turbulent flow is investigated using improved Delayed Detached-Eddy Simulation (IDDES) based on the shear stress transport k–omega model. A series of array configurations with systematically varied unit width and spacing are examined to clarify their influence on drag characteristics and flow-modulation behavior. The results reveal a strong competition between friction-drag reduction and pressure-drag generation. Net drag reduction is achieved only when these competing mechanisms are balanced. The findings highlight the importance of geometric parameter tuning in arrayed surface designs and provide qualitative insight into the comparative flow-modulation behavior induced by deformation-inspired surface structures. The present IDDES framework partially resolves the turbulence structures while modeling part of the near-wall flow. Therefore, the turbulence analyses presented here are primarily intended to reveal comparative trends among different configurations rather than fully resolved near-wall turbulence mechanisms.