A Color-Coded Single Camera Three-Dimensional Defocusing Particle Image Velocimetry System

A color-coded 3-D Defocusing Particle Image Velocimetry (3DDPIV) is a new modification of the 3-D measurement system originally developed by Willert {\&} Gharib (1992). It uses a single lens with 3 color-coded pinholes to overcome limitations of image saturation due to multiple exposures of each particle, and a 3-CCD color camera for image acquisition. The spectrum difference between the color filters and the CCD sensors is solved by a color space linear transformation, separating each pinhole's exposure. The requirement for a high intensity light source prevalent in conventional lighting setups is solved by backlighting the field-of-view and seeding the flow with black particles. An effective pinhole separation, $d'$, is proposed for use with multi-element lenses, and a multi-surface refraction correction to $d'$ is also proposed. Calibration results of the system with and without fluid are performed and compared. The technique is successfully applied to a buoyancy-driven flow, and a three-dimensional velocity field is extracted. The image volume is 3.25mm$\times $2.45mm$\times $1.5mm.