Benchmarking particle shadow velocimetry (PSV) with particle image velocimetry (PIV) using higher-order statistics

Planar PIV and PSV are used to measure the velocity of a fully-developed turbulent pipe flow at the 11.2” diameter glycerin tunnel at Penn State. The turbulent energy spectrum is calculated from both PIV and PSV, and compared. PSV is a type of PIV that uses an in-line backlight to illuminate particles, so shadows are recorded. The shadows are inverted as to appear as an image acquired using PIV. Because the inverted image will typically contain more out-of-focus particles, PSV has a higher noise level than PIV. While previous works by the authors suggest that the ability to estimate velocity based on PSV images should be similar to that of PIV images, more rigorous analysis is needed to examine how noise in PSV affects the measured velocity. To do this, PSV is used to measure velocity in a fully-developed turbulent pipe flow. Turbulence statistics, such as the mean velocity, velocity correlations, and turbulent energy spectrum, are obtained. These measurements are compared to those obtained using PIV at the same facility. It is expected that this will demonstrate the effectiveness of PSV as type of velocimetry akin to PIV, and encourage the use of PSV in the velocimetry world.