Improvement of the accuracy of PIV measurement of flow field in a levitated droplet

Abstract

The use of levitated droplets with electrostatic and ultrasonic fields has attracted much attention in the fields of materials development, chemical engineering, droplet-based microfluidics, inkjet printing, and aerospace engineering. To use them properly, it is essential to understand the internal flow of the suspended droplet. The flow inside fluid droplets is visualized with the particle image velocimetry (PIV) method. The fluid that is to be investigated is scattered with small particles that follow the flow well. One problem that occurs when the PIV method is used to measure velocity fields inside droplets is however that light refracts at the droplet surface and the internal flow curvature is distorted. The aim of this research is to improve the accuracy of PIV measurement by correcting the distorted particle images of an acoustically levitated droplet using calibration method. In this study, a simulated droplet with different refractive index and aspect ratio was used to investigate their influence on distortion correction. The circular target plate was also utilized to correct the distortion in a simulated droplet using a calibration method of the python-OpenCV. The experimental results showed that the internal flow curvature can be distorted in two types such as barrel, pincushion distortions, and increase as the refractive index increases. Therefore, correction of the distorted image of particles in the droplet showed good convergence as the aspect ratio decreased.

Keywords

• acoustic levitation
• aspect ratio
• calibration method
• droplets
• particle image velocimetry (piv)
• refractive index