Applying Holographic Particle Image Velocimetry to Sprays

Abstract

Measuring the velocity field of dispersed flows is of major importance in many applications, such as sprays and particle-laden jets. Traditional particle image velocimetry (PIV) setup is common in laboratories but it is limited to planar measurements. The objective of the present study was to conduct velocity measurements for sprays using HPIV. The present study involved extension of present holographic PIV method to spray fields. The present optical setup is based on inline digital holographic microscopy. Double-pulsed holograms were recorded and reconstructed to yield many two-dimensional slices (planes) of the flow field at two time instances. A large number of focused and unfocused drops appeared in each slice resulting in a lot of noise. Thus it was required to develop new image processing subroutines which could bypass the noise and consider only the focused droplets present in each plane while rejecting the shadow of non focused droplets not present in plane. Threshold subroutines help user to decide the signal to noise ratio in final processed images from hologram. The PIV correlation was used to calculate velocity from images processed with subroutines.