Online Event-Based Insights into Unsteady Flows with TrackAER

We present a novel event-based quantitative flow visualization system, TrackAER, capable of continuously reconstructing, rendering and recording particle tracks in large test volumes and without limitations to the measurement duration. Multiple event-based cameras are synchronized and calibrated to produce independent and asynchronous, yet temporally co-registered data streams of flow tracers. Subsequently, these data streams are merged into time-resolved 3D particle tracks using photogrammetric techniques. Due to the operating principle of event cameras, the flow scenery is reduced to moving objects only, which effectively compresses the data stream at the camera source. In combination with an efficient data processing pipeline, the measurement system operates online. That is, the investigated flow field is reconstructed and rendered in an interactive 3D viewer without noticeable time lag. The data processing approach follows a “per-event” paradigm and is achieved in real-time, enabling the immediate observation and analysis of both, transient and long duration flow features. Specific issues resulting from event-based, frame-free processing are discussed as well as the advantages and limitations of event cameras. Exemplary results of two different test cases are provided to demonstrate the utility of the TrackAER system in- and outside a wind tunnel, where Lagrangian particle track information is displayed in a virtual scene together with extracted quantitative information such as local flow velocities.