The evolution of particle image velocimetry (PIV) from its various roots is discussed. The importance of these roots and their influence on different trends in the speciality are described. The state-of-the-art of the technique today is overviewed and illustrated by reference to recent, seminal publications describing both the development and application of PIV.

Particle image velocimetry: A review

Every mariner is aware that dangerous large breaking water waves occur on the world's oceans. The scope of this review is somewhat greater. Wave breaking occurs at a large range of scales and we do not restrict ourselves to the deep ocean. "Deep water" in the context of water wave studies implies water sufficiently deep that the surface waves are unaffected by the direct effects of variations in bed topography. Thus even a small pond can support breaking deep-water waves. Shallow water breaking is reviewed in Peregrine (1983). Some comments on the visual aspect of breakers are in order, since direct observation still has a role to play in the study of this complex phenomenon. The most dramatic breakers are plunging breakers where the breaking commences by the wave overturning and forming a forward moving sheet of water which plunges down into the water in front causing splashes, air entrainment, and eddies. Although plunging breakers are common on beaches they are less common on deep water, so much so that some people have argued that they do not occur naturally. However, read Coles (1991) for a distillation of an experienced yachtsman's account of waves at sea. Most other breakers are described as spilling breakers. From their

Wave Breaking in Deep Water

The measurement of velocity fields of a plunging wave impacting on a structure in a two-dimensional wave tank was investigated experimentally. As the wave impinged and overtopped the structure, a large highly aerated region was created in front of the structure and on top of the structure. The broken wave in front of the structure and associated greenwater on top of the structure are highly aerated containing not only a large number of bubbles but also very large sizes of bubbles. The highly aerated bubbly flow caused the traditional particle image velocimetry (PIV) technique to fail due to the uncontrollable scattering of laser light. A modified PIV method, called bubble image velocimetry (BIV), was introduced by directly using bubbles as the tracer and measuring the bubble velocity by correlating the 'texture' of the bubble images. No laser light sheet was needed while the depth of field was limited to minimize the error. Velocity measurements using BIV and fibre optic reflectometer were compared to validate the BIV technique. While the fluid velocity in the region where no or few bubbles exist can be successfully obtained using PIV, the velocity in the high void fraction region can be measured using BIV. Therefore, BIV can be seen as a complementary technique for PIV. The use of BIV is essential in the studied problem here due to the fact that in the vicinity of the structure the flow is almost entirely bubbly flow. From both the PIV and BIV measurements, it was found that the maximum fluid particle velocity as well as the bubble velocity in front of the structure during the impinging process is about 1.5 times the phase speed of the waves.

https://iopscience.iop.org/article/10.1088/0957-0233/16/10/009/pdf

Use of bubble image velocimetry for measurement of plunging wave impinging on structure and associated greenwater

Plunging breaking waves are generated mechanically on the surface of essentially deep water in a two‐dimensional wave tank by superposition of progressive waves with slowly decreasing frequency. The time evolution of the transient wave and the flow properties are measured using several experimental techniques, including nonintrusive surface elevation measurement, particle image velocimetry, and particle tracking velocimetry. The wave generation technique is such that the wave steepness is approximately constant across the amplitude spectrum. Major results include the appearance of a discontinuity in slope at the intersection of the lower surface of the plunging jet and the forward face of the wave that generates parasitic capillary waves; transverse irregularities occur along the upper surface of the falling, plunging jet while the leeward side of the wave remains very smooth and two dimensional; the velocity field is shown to decay rapidly with depth, even in this strongly nonlinear regime, and is simila...

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An experimental study of deep water plunging breakers

We describe an experimental investigation of various methods of using the non-intrusive particle image velocimetry (PIV) technology to obtain the acceleration field of fluid flows and particularly the force being exchanged between a fluid flow and its boundaries. Methods based on the Lagrangian and the Eulerian specifications respectively have been developed, applied to experiments and compared. The experiments were performed by using a four-CCD-camera system designed to acquire between two and four frames in a fast time sequence, to provide single- or multiple-exposure PIV images of general fluid flows. The experiments involved various types of surface waves impinging upon a vertical wall at the end of a flume. Simultaneous monitoring with various transducers provided the experimental evaluation of the force predictions, whereas numerical simulations and PIV measurements have been used to validate the techniques for determining accelerations.

https://iopscience.iop.org/article/10.1088/0957-0233/8/12/013/pdf

Particle image velocimetry for predictions of acceleration fields and force within fluid flows

Instantaneous, full-field velocity measurements under the crest of a laboratory generated breaking wave are presented and compared with a fully non-linear time-stepping numerical model. A plunging breaker is generated, on constant water depth, using the numerical model, then reproduced in a wave flume by matching wave amplitude timeseries at a position just before the breaking. The generation of the waves is achieved by means of a computer controlled wave paddle and measurements of the flow made with a full-field photographic technique (PIV). The photographic records of the flow are analysed on an automatic rig and the measurements are shown to compare well with the numerical calculations.

C. Gray

Papers

A comparison of time-stepping numerical predictions with whole-field flow measurement in breaking waves