Measurements of instantaneous velocity fields could be done with the time and place high-resolution Particle-Image-Velocimetry (PIV). This technique is a scientific tool for qualitative and quantitative investigations of flow fields. The following figure shows the principle of PIV.
DPIV is based on the principle to capture the image of the flow field two times. A pulsing Dual-Nd:YAG laser is used. This device is specified by a wavelength of 532 nm, a pulse frequency of 15 Hz, a minimum pulse delay of 3 µs and a maximum pulse energy of 120 mJ. In the flow there are tracer particles with an average size of 1 µm. These particles reflect in the laser light sheet, which is formed with a light sheet optic consisting of a system of one spherical and two cylindrical lenses. It generates a light sheet with a thickness of 1 mm. The high resolution CCD camera takes one (Single- Frame) or two pictures (Double-Frame), depending on the pulsing laser. Each picture has a size of 2.5 MB. The CCD camera, perpendicularly positioned to the light sheet, is a so-called auto correlation camera or cross correlation camera having single-frame double-exposure or double-frame single-exposure evaluation. Now it is possible to calculate the value, direction and orientation of the absolute velocities with the Auto Correlation Function (ACF) or Cross Correlation Function (CCF).