Particle image velocimetry: image labeling by use of adaptive optics to modify the point-spread function

Area of Science:

• Fluid dynamics
• Optical engineering
• Image processing

Background:

• Particle-image velocimetry (PIV) is a key technique for measuring fluid flow.
• Accurate PIV analysis requires distinguishing between sequential image exposures.
• Current methods for image labeling can be complex or inefficient.

Purpose of the Study:

• To present a simple and effective method for labeling sequential images in PIV recordings.
• To enable independent spatial filtering and cross-correlation analysis of individual exposures.
• To enhance the accuracy and applicability of PIV measurements.

Main Methods:

• A rotating optic is inserted into the iris plane of the camera objective to alter optical transfer characteristics between exposures.
• Spatial filtering is employed to selectively address images from each exposure.
• Two systems are demonstrated: one using an aperture plate and another using a phase plate.

Main Results:

• The developed method successfully labels first- and second-exposure images.
• Spatial filtering allows for independent processing of the labeled images.
• The phase plate system demonstrates significantly higher light efficiency compared to the aperture plate system.

Conclusions:

• The presented technique offers a straightforward approach to image labeling in PIV.
• This method facilitates robust cross-correlation analysis for accurate flow field determination.
• The phase plate implementation is a promising, light-efficient solution for high-speed flow visualization.