Benchmark evaluation of event-based imaging velocimetry using digital micro-mirror device

Abstract

A benchmark evaluation of event-based imaging velocimetry (EBIV) on its acquisition capability and measurement uncertainty is performed. Toward this end, a digital micro-mirror device interfaced with a pulsed laser light source is employed to generate illuminated particle images under various predefined particle diameters and concentrations, serving as the ground-truth base. For ease of comparison, a frame-based camera is used to provide the reference particle images. The measurement results indicate that the maximum frame-recovered acquisition frequency decreases as either particle image diameter or concentration increases, converging to a minimum level of 2400 Hz for the EVK4 event-based camera. Despite this lower limit of frequency, adding large-diameter and high-concentration particles may induce event overflow and then lead to incorrect velocity measurements. This deficiency can be avoided by maintaining a margin of around 5% between the maximum acquisition frequency and its lower limit, which corresponds to frequencies over 2500 Hz in this study. Furthermore, for an acquisition frequency over 2500 Hz, a diameter of 2.20 px exhibits the lowest mean velocity uncertainty, whereas, for an acquisition frequency below 2500 Hz, diameters of 2.20 and 3.06 px can both achieve the lowest uncertainty level. A linear model is also proposed to predict the maximum acquisition frequency in practical applications. This work establishes the relationship among acquisition frequency, measurement uncertainty, particle size and concentration for the EBIV system. Finally, a two-dimensional EBIV experiment on a water jet is successfully conducted at 4 kHz.