Drag reduction by a solid wall emulating spanwise oscillations. Part 1

TL;DR

This paper proposes a novel turbulent drag reduction method using a specially shaped solid wall that emulates spanwise oscillations, potentially reducing skin friction by about 2.4% based on theoretical estimates.

Contribution

The study introduces a new approach to turbulent drag reduction by designing wall shapes that mimic spanwise oscillations, offering an alternative to in-plane wall motion techniques.

Findings

Estimated 2.4% drag reduction with a wavy wall design.

Optimal wave crests form a 38-degree angle with flow.

Wave period in main flow direction is about 1500 wall units.

Abstract

A new idea for turbulent skin-friction reduction is proposed, wherein the shape of the solid wall is designed to create the spanwise pressure gradient acting similarly to the well-known method of drag reduction by in-plane spanwise wall motion. Estimates based on the assumption of similarity with drag reduction effect of in-plane wall motion suggest that drag reduction of about 2.4% can be achieved in the flow past a wavy wall, with the crests forming an angle of about 38 degrees with the main flow direction, and the wave period in the main flow direction equal to about 1500 wall units. The required height of the wall waves have to be adjusted to achieve the same intensity of the spanwise motion as that created by an in-plane moving wall of the same wavelength and with peak wall velocity equal to 2 wall units. Further research is being conducted in order to determine this height. Suggestions are made for further research on confirming the feasibility of the proposed method and on optimising the wall shape.