Passive stabilization of crossflow instabilities by a reverse lift-up effect

TL;DR

This paper introduces a passive stabilization mechanism called the reverse lift-up effect, where a spanwise-invariant surface feature dampens crossflow instabilities in boundary layers, with potential applications in laminar flow control.

Contribution

The paper identifies a novel passive stabilization mechanism for crossflow instabilities via a reverse lift-up effect and develops a theoretical framework applicable to various 3D flows and surface geometries.

Findings

Spanwise-invariant surface features can significantly stabilize crossflow instabilities.

The reverse lift-up effect transfers energy from shear-flow instabilities to the laminar flow.

A general theoretical framework for energy transfer mechanisms in 3D flows is presented.

Abstract

A novel mechanism is identified, through which a spanwise-invariant surface feature (a two-dimensional forward-facing step) significantly stabilizes the stationary crossflow instability of a three-dimensional boundary layer. The mechanism is termed here as reverse lift-up effect, inasmuch as it acts reversely to the classic lift-up effect; that is, kinetic energy of an already existing shear-flow instability is transferred to the underlying laminar flow through the action of cross-stream perturbations. To characterize corresponding energy-transfer mechanisms, a theoretical framework is presented, which is applicable to generic three-dimensional flows and surface features of arbitrary shape with one invariant spatial direction. The identification of a passive geometry-induced effect responsible for dampening stationary crossflow vortices is a promising finding for Laminar Flow Control applications.