Cross-correlation - Holographic particle image velocimetry

It is still one of the main problems to observe and measure the non-steady and spatial complex flows for the fluid mechanics. Except 2D-PIN and SPIV, the Holographic Particle Image Velocimetry ( HPIV) is one of the approaches to measure instantaneously the three component ( u, v, w) velocity vector field in a full 3D volume ( space). In this paper, the displacements of the particles in a volume of the flow was recorded instantaneously by a holographic recording system which was designed and tested specially. Using the two exposure pulses of YAG lasers separately, the diffused illuminating lights and the reference lights with a symmetric optical arrangement using a beam-combiner-splitter device (BCS), it could have the reconstruction of the holographic fields of the particles with different exposures time and use the cross-correlation method to determinate the directions of the displacements of the particles. Using the stereoscopic PIV ( SPIV) technique here, the particle images of every sectional view with a certain thickness (or equivalent the depth of field for the camera) in the holographic volume could be captured with stereoscopic method. Finally the instantaneous 3-component velocity vector field in a 3-dimensional volume of the flow was provided. Also some cross-correlation image processing methods, the three dimensional geometry match and calibration of the holographic reconstruction images and the error evaluation were discussed. The HPIV technique here was applied to a diagonal flow passed a cubic bos ( 100x100x100 mm(3)) and some results of the instantaneous 3 -component velocity vector field in a 3 -dimentional volume of a cubic bos flow were given.