Three-dimensional particle velocimetry

Light sheet particle image velocimetry (PIV), which renders an instantaneous record of in-plane components of the flow velocity throughout the sheet, is the starting point for the review of techniques to determine the three-dimensional velocity vector within an extended flow volume. The analysis is restricted to particle velocimetry. The accuracy of particle localization is given by the limits of high-resolution imaging. More traditional variations of PIV like coding of the depth position in the sheet or scanning laser sheets are mentioned. Stereo PIV yields the out-of-plane velocity component and provides an understanding of basic relations for depth resolution. A novel back-projection scheme minimizes distortion effects and leads the way to a sophisticated phase conjugate evaluation of holographic images. Particle holography is introduced and the performance of various configurations like in-line, off-axis or multiple light sheet holography for flow applications is discussed. The paper presents the state of the art in practical applications and provides material to assist in the selection of the method best suited for a given task.