Abstract

This and the next chapter deal with different measurement techniques of turbulence and associated phenomena, such as two-phase flows or surface and internal wave generations. During the last 40 years, the main efforts were focused on the study of coherent structures in turbulence that are of medium or large size (big or intermediate eddies). To reach this goal one should have the ability to conduct simultaneous measurements of spatial flow patterns at a great number of points, on the one hand. On the other hand, there is a necessity to focus on the study of turbulence microstructures, enabling measurements of velocity derivatives’ tensor, vorticity, dissipation, and enstrophy generation that require very high spatial resolution. New technologies emerging all the time have helped to develop new instruments, such as multi-arrays assembled of conventional single sensors (hot-wires/films) possessing very small volumes in space and providing a very high time response and comprehensive optical devices featuring the entire flow pattern in plane, or even in volume, by tracking solid particles or air bubbles: particle tracking velocimetry (PTV), particle image velocimetry (PIV), laser Doppler anemometry (LDA), fiber optic sensors for detection of void fraction in two-phase flow, and planar laser-induced fluorescence (PLIF) for concentration field measurements.