Abstract
All the principal techniques of flow visualization in water are reviewed, consideration also being given to the possibility of obtaining quantitative information from them. Static methods illustrate the pattern of velocity gradient at the surface of a solid boundary and are particularly valuable in indicating transition and separation of the boundary layer. Many kinetic methods involve the observation of tracer particles, either solid or bubbles of another fluid; the associated hydrodynamic and optical problems are discussed. Some of these methods may be adapted to indicate three-dimensional flow. Techniques based on streaming birefringence are reviewed but, for quantitative results, are found wanting. Chemical methods largely avoid the hydrodynamic problems but often have practical drawbacks. Among electrolytic methods that using hydrogen bubbles is remarkably versatile and now seems supreme; this technique is therefore discussed in some detail.