High-resolution volumetric flow measurements in a transverse shear layer between two angled streams, using Colored Tomographic Particle Shadow Velocimetry.

We measure the full volumetric velocity field in a transverse shear layer between two angled streams. The flow is set up in two in-house designed rectangular 3D-printed channels, having the same flow rate driven by independent centrifugal pumps, but angled in the horizontal direction and separated by a splitter plate. Polyamide particles are fed into the flow through holes embedded near the edge of the splitter plate. We use four high-resolution 12k (Blackmagic) video cameras from different angles to capture particle shadows using the Colored Tomographic Particle Shadow Velocimetry technique [1][2]. By pulsing a set of three differently colored LEDs, red – green – blue, during a single frame exposure, we can triple the base recording frame rate without significantly sacrificing spatial sensor resolution by encoding the temporal information in the color of the particle shadows. Therefore, we can increase our base frame rate from 24 fps to 72 fps. The timing between pulses is controlled with a digital delay generator. We preprocess the recorded images to separate the three different color fields by using hue values masks and minimizing noise. The resulting images are then processed with commercial software to obtain the full 3D-3C flow velocimetry with LaVision Shake-The-box and Tomographic-PIV algorithms.