Cavitation Monitoring and Coherent Structure Identification using Event Cameras

Event cameras are bio-inspired sensors that measure logarithmic changes in image intensity and have seen increased use in recent years due to their high dynamic range, low data output rates, and high temporal resolution. Imaging cavitating flows is challenging, as the phenomenon is inherently high-speed, can be intermittent, and the air/water interface reduces optical access. We demonstrate that event cameras can address many of these shortcomings, with significant reductions in data rate, alongside improvements in the identification of internal features. We perform simultaneous high-speed and event camera measurements of a nozzle undergoing unsteady cloud cavity shedding. The high dynamic range of the event cameras allows for the observation of time-averaged internal features in the cavitation cloud; these features qualitatively match with regions of high void fraction obtained with x-ray densitometry, yet which could not be observed with conventional high-speed cameras. Dynamically, the dominant shedding frequency is captured well with the event and high-speed camera; however, corrections must be applied to the event camera for accurate frequency measurements. These corrections are inherent to the operating principle of the camera and extend to applications beyond cavitation.