Principles and Techniques of Schlieren Imaging

Abstract

This paper presents a review of modern-day schlieren optics system and its application. Schlieren imaging systems provide a powerful technique to visualize changes or nonuniformities in refractive index of air or other transparent media. For over two centuries, schlieren systems were typically implemented for a wide variety of non-intrusive real-time fluid dynamics studies. With the popularization of com- putational imaging techniques and widespread availability of digital imaging systems, schlieren systems provide novel methods of viewing transparent flow. Innovations such as background-oriented schlieren, rainbow schlieren interferometry, and synthetic schlieren imaging have built upon the fundamentals of schlieren imaging to provide less ambiguous, quantifiable studies of schlieren systems. This paper presents a historical background of the technique, describes the methodology behind the system, presents a mathematical proof of schlieren fundamentals, and lists various recent applications and advancements in schlieren studies. Contents