Three Dimensional Interactions And Vortical Flows With Emphasis On High Speeds

The objective of this research is the basic theoretical investigation of three-dimensional pressure, skin friction, and heat transfer disturbances in both laminar and turbulent boundary layer flows including viscous-inviscid interaction effects, separation, and reattachment. A sound understanding of these phenomena is required in modern aerodynamic design analyses of high-speed flight vehicles. The primary emphasis in these studies has been to seek a basic physical understanding of the underlying fluid behavior by means of analytically-oriented methods; in this way, the results can be used to guide and interpret concurrent experimental and computationally-oriented investigations. This inquiry has focused on two parallel paths of investigation: three-dimensional, viscous-inviscid interaction phenomena within turbulent boundary layers in supersonic flow due to impinging swept shock and/or 3-D surface deflections, and streamwise vortex-disturbance mechanisms within laminar or turbulent boundary layers that are either separated or attached.

Viscous flow is treated usually in the frame of boundary-layer theory and as two-dimensional flow. Books on boundary layers give at most the describing equations for three-dimensional boundary layers, and solutions often only for some special cases. This book provides basic principles and theoretical foundations regarding three-dimensional attached viscous flow. Emphasis is put on general three-dimensional attached viscous flows and not on three-dimensional boundary layers. This wider scope is necessary in view of the theoretical and practical problems to be mastered in practice. The topics are weak, strong, and global interaction, the locality principle, properties of three-dimensional viscous flow, thermal surface effects, characteristic properties, wall compatibility conditions, connections between inviscid and viscous flow, flow topology, quasi-one- and two-dimensional flows, laminar-turbulent transition and turbulence. Though the primary flight speed range is that of civil air transport vehicles, flows past other flying vehicles up to hypersonic speeds are also considered. Emphasis is put on general three-dimensional attached viscous flows and not on three-dimensional boundary layers, as this wider scope is necessary in view of the theoretical and practical problems that have to be overcome in practice. The specific topics covered include weak, strong, and global interaction; the locality principle; properties of three-dimensional viscous flows; thermal surface effects; characteristic properties; wall compatibility conditions; connections between inviscid and viscous flows; flow topology; quasi-one- and two-dimensional flows; laminar-turbulent transition; and turbulence. Detailed discussions of examples illustrate these topics and the relevant phenomena encountered in three-dimensional viscous flows. The full governing equations, reference-temperature relations for qualitative considerations and estimations of flow properties, and coordinates for fuselages and wings are also provided. Sample problems with solutions allow readers to test their understanding.

In this book, recent developments in our understanding of fundamental vortex ring and jet dynamics will be discussed, with a view to shed light upon their near-field behaviour which underpins much of their far-field characteristics. The chapters provide up-to-date research findings by their respective experts and seek to link near-field flow physics of vortex ring and jet flows with end-applications in mind. Over the past decade, our knowledge on vortex ring and jet flows has grown by leaps and bounds, thanks to increasing use of high-fidelity, high-accuracy experimental techniques and numerical simulations. As such, we now have a much better appreciation and understanding on the initiation and near-field developments of vortex ring and jet flows under many varied initial and boundary conditions. Chapter 1 outlines the vortex ring pinch-off phenomenon and how it relates to the initial stages of jet formations and subsequent jet behaviour, while Chapter 2 takes a closer look at the behaviour resulting from vortex ring impingement upon solid boundaries and how the use of a porous surface alters the impingement process. Chapters 3 and 4 focus upon the formation of synthetic jets from vortex ring structures experimentally and numerically, the challenges in understanding the relationships between their generation parameters and how they can be utilized in flow separation control problems. Chapter 5 looks at the use of imposing selected nozzle trailing-edge modifications to effect changes upon the near-field dynamics associated with circular, noncircular and coaxial jets, with a view to control their mixing behaviour. And last but not least, Chapter 6 details the use of unique impinging jet configurations and how they may lend themselves towards greater understanding and operating efficacies in heat transfer problems. This book will be useful to postgraduate students and researchers alike who wish to get up to speed regarding the latest developments in vortex ring and jet flow behaviour and how their interesting flow dynamics may be put into good use in their intended applications.

A combined analytical experimental program, which has as its continuing objective the detailed investigation of the three dimensional vortex interactions which take place in turbulent boundary layers, is described and the accomplishments detailed. The analytical and numerical studies have examined both the development and characteristics of loop and hairpin vortices in both uniform and shear flows; particular attention has been paid to the strong three dimensional, inviscid viscous interaction of these types of vortical flow structures with wall region fluid. The experimental studies have focussed on the creation & detailed examination of three dimensional hairpin vortices, developing flow visualization patterns for cross-comparison with both the analytical studies and fully turbulent boundary layer flows. A technique for developing quantitative data by image processing of the visualization patterns is also described. Keywords: Turbulent boundary layer; Coherent structure; Flow visualization; Numerical modelling; Vortex wall interactions; Computer aided analysis; Loop vortices; Hairpin vortices.