Design and analysis of micro-nano scale nested-grooved surface structure for drag reduction based on 'Vortex-Driven Design'

Bioinspired grooved surface structure design has been widely used as an efficient passive flow control method in drag reduction. The total drag of plate with grooved surface structure can be decomposed into friction and pressure drag. In this paper, the relationship between them and the distribution of vortex structure in flow field has been analyzed for obtaining the drag reduction mechanism of grooved surface structure. The concept of 'Vortex-Driven Design' is proposed to improve the performance of conventional periodic single-level grooved surface structure. A design scheme of micro-nano scale nested-grooved surface structure with better drag reduction performance is given. The authors conduct numerical simulation of rectangular nested-grooved surface structure in laminar flow considering rarefaction based on Lattice Boltzmann Method at high Knudsen number. The results show that the nested-grooved surface structure induces higher complexity in the secondary vortex structure, and that the changes of vorticity distribution and flow characteristics drive the changes of velocity distribution and shear stress in the grooved surface. Compared with conventional grooved surface structure, the average friction drag of the surface is further reduced. Two geometric optimization cases of the conventional grooved surface and nested-grooved surface are realized by Genetic Algorithm, showing that the maximum drag reduction rate of the optimal nested-grooved surface can reach 18.76% while that of the optimal conventional grooved surface only reaches 13.61%. Based on 'Vortex-Driven Design', an innovative material improvement method for drag reduction is proposed as a new direction for subsequent research on microstructure in terms of drag reduction and energy conservation. (C) 2020 Elsevier Masson SAS. All rights reserved.

Automated summary

This paper analyzes the relationship between friction drag and pressure drag of grooved surface structure, as well as the distribution of vortex structure in the flow field, to reveal the drag reduction mechanism. The concept of 'Vortex-Driven Design' is proposed, and a design scheme of micro-nano scale nested-grooved surface structure with better drag reduction performance is introduced. Numerical simulations show that the nested-grooved surface structure induces higher complexity in the secondary vortex structure and significantly reduces friction drag.