Confetti Velocimetry: Time-Resolved Flow Imaging with Six-Color Particle Shadows.

We present an enhanced Particle Shadow Velocimetry (PSV) technique that utilizes six distinct background colors to significantly increase the effective temporal resolution. This is achieved by sequentially flashing colored LEDs—first the primary colors (Red, Green, Blue), followed by their additive combinations (Magenta, Cyan, Yellow)—within a single camera exposure. As a result, each particle produces six color-coded shadows corresponding to discrete time intervals, effectively multiplying the frame rate of a standard color camera by six while minimizing the loss of spatial resolution. Temporal information is thus encoded in the color of each shadow, enabling time-resolved flow measurements using a single frame exposure. However, this approach introduces challenges related to accurate color separation and the potential for shadow overlap, requiring robust image processing strategies. To address these, we implemented a color-splitting algorithm based on HSV color space and validated it using synthetically generated data. The technique was further tested in experimental setups, including channel flow and jet flow devices, using a cost-effective commercial high-speed color camera. Velocity fields were subsequently extracted using both cross-correlation and particle tracking velocimetry (PTV) methods. This multi-color PSV approach offers a scalable and low-cost solution for high-temporal-resolution flow diagnostics.