Measurement Techniques

2D Particle Image Velocimetry (PIV), Stereoscopic 3D Particle Image Velocimetry

Particle image velocimetry (PIV) can measure the flow velocity in 2D planes by tracking small tracer particles. A laser sheet illuminates the particles, and a camera captures a pair of particle images. The images are divided into multiple interrogation windows. Velocity vectors can be obtained in each interrogation window by cross correlation and the time separation between the two frames. An instantaneous velocity vector field for homogeneous isotropic turbulence (HIT) is displayed in the left box.

Stereoscopic PIV is an advanced method, which can measure the flow velocity of 3 components (x, y, z direction) in a 2D plane. Based on the same principle as human eyesight, two cameras are placed at an angle (i.e. Scheimpflug condition) for perceiving the out-of-plane displacement of particles. Each camera takes images of particles within the laser sheet. Since the cameras are at an angle, the images are initially distorted. Image distortion is later removed, which allows the out-of-plane displacement to be calculated by the formula in the right box. The instantaneous in-plane velocity field (shown by vectors) is displayed with the out-of-plane velocity (shown by the colormap) for homogeneous isotropic turbulence (HIT), in the right box.

We are applying PIV in various applications such as fundamental turbulence, particle-laden flows, flow around gas turbine blades and drones.