Special issue on global flow instability and control

Abstract

This special issue is intended to provide a snapshot of current research in the área of "Global Flow Instability and Control". The original papers, and to a certain extent the topic itself, are intimately linked with the series of symposia by the same ñame that were held in Crete, Greece, between 2001 and 2009. As members of the organizing committees of the Crete symposia, we invited all past participants to contribute, and all papers were reviewed following the strict standards of the journal. This preface gives a brief historical account of events that have shaped ideas in the fleld over the past decade, followed by a synopsis of the papers published herein. Keyword Global flow instability and control The Crete meetingsIn July 1998, Peter Duck and Anatoly Ruban organized the EUROMECH 384 CoUoquium on "Steady and Unsteady SeparatedFlows" in Manchester, with Sir James Lighthill as the keynote speaker. The proceedings of this colloquium were published as a Research Frontiers issue, volume 358, of the Philosophical Transactions of the Royal Society London journal. The preface of that issue contains the colourful hand-written transparencies of Sir James, which were bound to be the last scientiflc document written by this towering fluid mechanics figure. A summary versión of another set of hand-written colourful drawings, corresponding to the hour-long presentation of Uwe Dallmann on flow topology [6], was included as the last chapter of the three-part paper by Theofilis, Hein and Dallmann [39] and provided a qualitative description of the first quantitative discovery, via a partial-differential-equation (PDE)-based eigenvalue problem (EVP) solution, of what is now commonly called global mode of a laminar separation bubble. One of the highlights in the prematurely ended scientiflc career of Uwe Dallmann was the enthusiastic appreciation of his flow topology work by Sir James, which is only natural, given that the first appearance of the association between flow separation and flow topology was the work of Lighthill himself in the classic textbook of Rosenhead [19].

Structural changes of laminar separation bubbles induced by global linear instability

“…The structure of the eigenfunctions corresponding to the leading eigenmode for the different basic flows is qualitatively identical to the one shown in figures 2 and 3, and exhibit the same characteristics of those known from earlier work on the flat plate and from instability analysis of related flows (Theofilis et al 2002;Gallaire et al 2007;Robinet 2007;Abdessemed et al 2009;Kitsios et al 2009;Marquet et al 2009). …”

“…In the last decade instability analyses based on solutions of partial-derivative eigenvalue problems (often referred to as BiGlobal analyses, Theofilis 2003) and/or DNS have elucidated global instability mechanisms in a variety of LSB flows, including the aforementioned adverse-pressure-gradient flat-plate flow , backward-facing step flow , as well as geometry-induced separation (Marquillie & Ehrenstein 2003;Gallaire, Marquillie & Ehrenstein 2007), NACA 0012 airfoil in incompressible (Theofilis, Barkley & Sherwin 2002) and compressible flow (Crouch, Garbaruk & Magidov 2007), low-pressure-turbine flow (Abdessemed, Sherwin & Theofilis 2004, 2009), shock-induced separation (Boin et al 2006;Robinet 2007), open cavity (Akervik et al 2007) and S-shaped duct flows (Marquet et al 2008(Marquet et al , 2009. In all configurations examined consensus has been built that two different primary instability mechanisms coexist.…”

On the birth of stall cells on airfoils

“…There too the origin of the topological changes lies with the global flow eigenmode. While in terms of amplitude function stmctures the leading eigenmodes of separated flow on the flat píate and the stalled wing share their principal characteristics, a result established through research on other types of airfoils and low-pressure-turbines [27,1], the absence of the trailing edge in the flat píate is responsible for the differences in the respective surface streamlines topology.…”

Global mode-based control of laminar and turbulent high-speed jets

“…Global mode analysis complements these approaches in that it provides a direct means of analyzing the behavior of linear disturbances whose superposition can replicate a wavepacket character. Theofilis [16] and Theofilis and Colonius [17] review the use of global modes while Jordan and Colonius [1] review wavepackets as a model for low-frequency jet noise. Although they are more computationally intensive to compute than PSE modes, global modes are more faithful to the full ✩ Financial support from the United States Office of Naval Research (Drs.…”