PTV measurement on interaction between two immiscible droplets and turbulent uniform shear flow of carrier fluid

Abstract

A flow visualization and a particle-tracking-velocimetry measurement have been conducted for a turbulent water plane Couette flow with two oil droplets in the central region in order to elucidate the effect of secondary flow induced by the droplets on the modification of shear-dominant turbulence. The diameters of these droplets are about 80 times larger than the micro scale of turbulence. The tracer particles coated with fluorescence color and the optical filter for the video camera is found to be effective for diminishing the reflected light from the interface and the moving wall. The experimental results show that zero-velocity regions exist near the interface around the axis because the direction of the wall-normal secondary flow is opposite to that of water moving with the rotating droplets. It is also found that the turbulence intensities in the region between the two droplets and in the small regions for the confluence and stagnation are attenuated due to the weakening of the wall-normal secondary flow particularly in the case where the distance between the centers of the two droplets is twice as long as the droplet diameter.