Plasma virtual roughness elements for cross-flow instability control

Kwing-So Choi,Jung-Hoon Kim

doi:10.1007/s00348-018-2609-x

Abstract

Recent experiments and numerical simulations demonstrated that discrete roughness elements can be used to control cross-flow instability over a swept wing. Here, the application of this passive technique requires a row of thin cylindrical elements of a few microns high immediately downstream of the leading edge to excite the subcritical modes of cross-flow instability. By properly choosing the spanwise spacing of these roughness elements, one can suppress the growth of most unstable modes, thereby delay transition. However, this passive technique of controlling cross-flow instability is very sensitive to the size (diameter and height), shape and location of discrete roughness. To mimic the discrete roughness elements and to be able to adjust the roughness parameters dynamically, virtual roughness elements based on dielectric-barrier-discharge plasma actuators have been developed and tested. In this paper, we show the plasma-induced flow field of several different prototype virtual roughness elements for cross-flow instability control, by describing the mechanisms of vortex generation from the virtual roughness elements through an interaction with the incoming laminar boundary layer.Graphical abstract

Highlights

The boundary layer developing over a swept wing is highly three-dimensional
We have developed several different types of dielectric-barrier-discharge (DBD) plasma actuators for cross-flow control by mimicking the discrete roughness elements, which we call plasma virtual roughness elements
Dielectric barrier discharge (DBD) plasma actuators are new breed of flow control actuators based on low-temperature plasma (Moreau 2007; Corke et al 2010; Kriegseis et al 2016)

Summary

Introduction

The boundary layer developing over a swept wing is highly three-dimensional. While the velocity component normal to the leading edge is reduced as the uniform flow approaches the swept wing, the velocity component parallel to the leading edge is not affected, diverting the inviscid streamline outboard (Reed and Saric 1989). The transition to turbulence of the laminar boundary layer over a swept wing is usually dominated by the cross-flow instability rather than two-dimensional T–S (Tollmien–Schlichting) wave instability (Saric et al 2003). Dielectric barrier discharge (DBD) plasma actuators are new breed of flow control actuators based on low-temperature plasma (Moreau 2007; Corke et al 2010; Kriegseis et al 2016). They are fast-acting, all-electric actuators without moving parts, consisting only of a pair of (upper and lower) electrodes sandwiching a dielectric sheet (Wang et al 2013), see Fig. 1. DBD plasma actuators have been used as virtual devices, such as vortex generators, flaps, travelling wave makers and tip-clearance seals, where significant improvements in aerodynamic and flow control performance have been made (Choi et al 2015)

Methods

Results

Conclusion