Speckle Photography for Fluid Mechanics Measurements

Optical methods provide tools of growing importance in experimental fluid dynamics. Recent interest focuses on whole-field methods that yield more-dimensional instantaneous velocity data. Today's most well established technique is particle image velocimetry (PIV) that has matured into a commercially available powerful routine. Yet, there exist a variety of closely related methods that can all be combined under the heading of speckle photography, and which are specially adapted to each provide specific flow data. It is the merit of the present book to give an overview on the basic optics behind these methods and outline the scope of areas of application. The first half of the book is devoted to the presentation of the background, describing the formation and properties of speckle-fields, their application for metrological purposes and the evaluation of the recorded speckle patterns. The thorough coverage of evaluation methods from times when powerful video recording and computer processing were not available illustrates the historical challenge and familiarizes the reader with many basic optical relations. Applications to problems in fluid mechanics occupy the second half of the volume. One chapter deals with particle velocimetry, including its extension into three dimensions. The main emphasis, however, is on the utilization and characterization of flow inhomogeneities as they are produced by temperature, density or concentration variations. It is shown how these fluctuations affect the propagation of light and how an analysis of the changing speckle patterns can be utilized to extract flow data. Appropriate optical set-ups climax in tomographic flow diagnostics which is covered in detail. In view of the rapid progress in electro-optics and computer image processing, any book on optical metrology faces the severe problem of remaining up-to-date. CCD technology and processing algorithms have advanced since the book went to press. However, the basic physics presented remains a good guide to designing and evaluating the performance of a system and in assessing new application areas. Scientists and engineers in fluid dynamics will profit from reading the book as will students in advanced areas of applied optics. Klaus Hinsch