Editorial

Abstract

Applied Mechanics Reviews (AMR) is an international review journal that serves as a premier venue for state-of-the-art and retrospective survey articles and reviews of research areas and curricular developments across all sub-disciplines of applied mechanics and engineering science, including fluid and solid mechanics, heat transfer, dynamics and vibration, and applications. AMR also provides a forum for dissemination of original tutorial articles. These organize novel insight and reflection on the use of one or several methods of modeling, design, analysis, or synthesis in an accessible format that can be used for guided instruction or self-study.This issue of Applied Mechanics Reviews expands upon original lecture notes delivered at a graduate-level Summer School on Advanced Instability Methods for Complex Flows, held in Stockholm, Sweden, in May 2013, and organized jointly by the Nordic Institute for Theoretical Physics (Nordita) and the Linné FLOW Centre at KTH Royal Institute of Technology.Nordita is a center for advanced research in theoretical physics with broad international participation. Nordita sponsors scientific programs in the form of extended workshops, where a limited number of scientists work together on specific topics for a period of up to 4 weeks. Program topics can range beyond the traditional borders of theoretical physics and include scientists in related areas of the natural sciences. The Linné FLOW Centre is one of 20 original centers of excellence created by the Swedish Research Council. Its mission is to solve a wide spectrum of problems with relevance for industry and society through fundamental research in fluid mechanics. The FLOW Centre also hosts a graduate school in fluid mechanics.The Summer School on Advanced Instability Methods for Complex Flows constituted the first week of the month-long Nordita program “Stability and Transition,” co-chaired by Ardeshir Hanifi, Dan Henningson, Luca Brandt, Jens Sørensen, Rama Govindarajan, and Shervin Bagheri. The aim of the overall program was to deepen the fundamental knowledge of stability and laminar-turbulent transition in fluid-flows by providing a forum for discussions between leading scientists from the Nordic countries and the rest of Europe, as well as from Asia and the Americas. Apart from the summer school, the program included four research themes:Stability and transition of flows belong to fundamental issues in the field of fluid mechanics with a wide range of applications to the engineering and natural sciences. Predicting flow structures and characteristics requires deep understanding of the different routes of transition. Recent developments in this area concern the adoption of concepts from optimization and control theory, as well as sensitivity and nonlinear modal analysis; these also enable an extension of the analysis from canonical to complex flows. The use of tools from dynamical system theory combined with numerical simulations has become crucial to the study and manipulation of flows in complex configurations.The lecture notes collected in this issue were developed to address the limited availability of educational material in this expanding area, on a topic important for the training and research of future scientists and engineers working on fluid-flow systems. Each paper expands upon material delivered during the 4 days of lectures, and includes exercises and project assignments similar to those worked on by students during the summer school. The four contributions are on modal stability theory (Juniper, Hanifi, and Theofilis), non-modal stability, receptivity and sensitivity (Schmid and Brandt), application of nonlinear dynamical systems to fluid mechanics (Govindarajan and Marathe), and optimal control applied to fluid flows (Cossu). Each is associated with auxiliary material, including computer codes for the proposed exercises and projects, which may be accessed through the ASME Digital Collection.We hope that this issue of AMR will provide a valuable collection of tutorial content that will support guided instruction and integration in existing graduate fluid mechanics curricula, as well as self-study and pedagogical reference.