Digital particle image velocimetry

Abstract

Digital particle image velocimetry (DPIV) is the digital counterpart of conventional laser speckle velocitmetry (LSV) and particle image velocimetry (PIV) techniques. In this novel, two-dimensional technique, digitally recorded video images are analyzed computationally, removing both the photographic and opto-mechanical processing steps inherent to PIV and LSV. The directional ambiguity generally associated with PIV and LSV is resolved by implementing local spatial cross-correlations between two sequential single-exposed particle images. The images are recorded at: video rate (30 Hz or slower) which currently limits the application of the technique to low speed flows until digital, high resolution video systems with higher framing rates become more economically feasible. Sequential imaging makes it possible to study unsteady phenomena like the temporal evolution of a vortex ring described in this paper. The spatial velocity measurements are compared with data obtained by direct measurement of the separation of individual particle pairs. Recovered velocity data are used to compute the spatial and temporal vorticity distribution and the circulation of the vortex ring.

DPIV Prediction of Flow Induced Platelet Activation—Comparison to Numerical Predictions

“…The maximum error of the DPIV technique is 5%. 20 Because of the huge amount of particle trajectories that can evolve either from a specific location or specific time point, an additional computational tool, which calculates the final cumulative activation level value of trajectories emanating from a specific seeding point for each time interval, was developed. This tool allowed an extensive investigation of the entire flow field to find trajectories that reach extreme values during the cycle.…”

“…The shutter speed determined the time between two successive frames, such that the local velocity field was obtained. 20 The DPIV system is based on continuous recording in real time of the investigated field. The video file produces consecutive frames at the camera frame rate (the sampling frequency of the flow field), as dictated by the NTSC video system used in this study.…”

Advances in the use of observed spatial patterns of catchment hydrological response

“…The method is a form of particle image velocimetry (e.g. [40,120]) and is based on cross-correlations between ''windows'' within the overall domain. A field of shift vectors can be calculated in the following way.…”

“…Willert and Gharib [120] describe a method using fast fourier transforms that significantly speeds up the computation of correlations.…”

On the accuracy of intracardiac flow velocimetry methods

“…Progress has been made to incorporate quantitative fluid dynamics into echocardiography using particle tracking algorithms [2,3,39] that are based mostly on the well-known optical imaging techniques of particle image velocimetry (PIV) [4][5][6] or color Doppler imaging [7][8][9][10]. Recent advances in understanding left ventricular (LV) fluid dynamics based on experimental methods [11][12][13][14] and numerical simulations [15][16][17] have shed light on many aspects of ventricular flow, such as the development of intraventricular vortices.…”