Particle image velocimetry - Classical operating rules from today’s perspective

Over the last four decades, particle image velocimetry (PIV) has evolved into a powerful and significant measurement technique. The technique has been applied to many areas of fluid mechanics and the accuracy and resolution has been greatly improved over the years. This was made possible by the creativity, enthusiasm and commitment of the developers, but also by the technical achievements in the field of tracer particles, light sources, recording systems, algorithms and computer power. Although time-resolved volumetric PIV measurements are possible today, the majority of measurements are still performed using planar PIV techniques for good reasons. First, planar PIV is rather simple to both install and use and the data is processed quickly and robustly. Second, in many cases planar PIV already provides the desired data to answer scientific questions. Due to the persistent interest in using planar PIV, it is the intention of this review to consider some classical operating rules from today’s perspective and to prove their validity. This may seem needless at first glance. However, it should be noted that once a technique has been established, the basic aspects are generally taken for granted. Therefore, a critical look from time to time is advisable to check whether the concepts are still valid or whether changes are necessary. Furthermore, we intend to deduce under which conditions the use of more complicated techniques pays off.