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The last two decades have witnessed an intensifying effort in learning how to manage flow turbulence: it has in fact now become one of the most challenging and prized techno logical goals in fluid dynamics. The goal itself is of course not new. More than a hundred years ago, Reynolds already listed factors conducive to laminar and to turbulent flow (including among them curvature and acceleration). Further more, it is in retrospect clear that there were several early instances ot successful turbulence management. Examples are the reduction in drag achieved with a ring-trip placed on the front of a sphere or the insertion of a splitter-plate behind a circular cylinder; by the early 1950s there were numerous exercises at boundary layer control. Although many of these studies were interesting and suggestive, they led . to no spectacularly successful practical application, and the effort petered out in the late 1950s. The revival of interest in these problems in recent years can be attributed to the emergence of several new factors. First of all, fresh scientific insight into the structure of turbulence, in particular the accumulated evidence for the presence of significant order in turbulent flow, has been seen to point to new methods of managing turbulence. A second major reason has been the growing realisation that the rate at which the world is consuming its reserves of fossil fuels is no longer negligible; the economic value of greater energy effi ciency and lower drag has gone up significantly.
Inhaltsverzeichnis
1 Wall-Bounded Flows.- 1A Structure.- Documentation of turbulence producing structures in regular and manipulated turbulent boundary layers.- Measurements in a synthetic turbulent boundary layer.- A unified view of the origin and morphology of the turbulent boundary layer structure.- 1B Outer Layer Devices.- Evaluation of drag reduction by turbulence control devices.- Turbulent boundary layer manipulation and modelling in zero and adverse pressure gradients.- Computational and experimental studies of LEBUS at high device Reynolds numbers.- Blade manipulators in channel flow.- 1C Surface Manipulation.- On the possibility of drag reduction with the help of longitudinal ridges in the walls.- Direct drag and hot-wire measurements on thin-element riblet arrays.- Viscous drag reduction using streamwise aligned riblets: survey and new results.- The wall pressure fluctuations of modified turbulent boundary layer with riblets.- Turbulence management by groove roughness.- A case for turbulence management by imposed wall excitation for fully developed turbulent flows - a numerical study.- 2 Transition.- 2A Dynamics.- The nature of oblique instability waves in boundary layer transition.- Transition of a boundary layer: controlled fundamental-subharmonic interactions.- Three-dimensional boundary-layer transition on a concave-convex curved wall.- Numerical simulation of transition in a decelerating boundary layer.- Measurement of nonlinear transfer functions for transitioning flows.- 2B Control.- Laminar-turbulent transition control by localized disturbances.- Suppression of unstable oscillations in a boundary layer.- Is the dolphin a red herring?.- The optimization of compliant surfaces for transition delay.- 3 Relaminarisation, Natural Laminar Flow.- Visualization ofrelaminarising flows: a colour movie.- On the process of inverse transition in radial flow between parallel disks.- Turbulent drag reduction and relaminarisation by xanthan gum.- All laminar supercritical LFC airfoils with natural laminar flow in the region of the main wing structure.- 4 Free Shear Flows.- On the pairing process in an excited, plane, turbulent mixing layer.- Experiments on turbulence control in jets and shear flows.- Excitation of azimuthal modes in an axisymmetric jet.- Passive and active control of jet turbulence.- Turbulent mixing in accelerating jets.- The mixing mechanism by organised turbulence structures in a plane jet excited by a novel method.- Performance of fluidically controlled oscillating jet.- 5 Separated Flows.- The structure and control of a turbulent reattaching flow.- Control of separated flow on a symmetric airfoil.
