Refractive index matched visualization and particle image velocimetry measurements of initial breakup of turbulent oil jet

Abstract

Subsurface oil well blowouts create buoyant, immiscible jets and plumes. Turbulent breaks jets into oil droplets with sizes ranging from several millimeters to sub-microns. The fate of oil droplets largely depends on their sizes. The physics of single thread of fluid breaks into several smaller droplets in low Reynolds number and Ohnesorge number can be well explained by Plateau-Rayleigh instability. However, when Reynolds number and Ohnesorge number are high, namely the atomization regime, the physics of high-speed jet fragments into a wide range of droplets is not well understood. Because of the opaque nature of crude oil, it is difficult to visualize and optically quantify the process of initial jet breakup and droplet generation within the zone of flow establishment (less than 10 nozzle diameters downstream). In order to overcome this issue, in this experimental study, two immiscible fluids (silicone oil, 64% v/v sugar water solution) with a matching index of refraction of nD=1.4015 are used as surrogates of crude oil and seawater. High speed visualization and particle image velocimetry (PIV) are implemented to study vertical turbulent oil jets of varying Reynolds and Ohnesorge numbers, all falling in the atomization range. The refractive index match enables light to pass through the test sample region with little refraction, thus providing undistorted images for flow visualization and quantitative measurements. The kinematic viscosity ratio voil/vaq = 5.64, density ratio ρoil/ρaq = 0.83, and interfacial tension σ = 28.8 mN/m between silicone oil and sugar water solution are closely matched with those of crude oil and seawater. Entrainment of the aqueous phase by the high speed oil jet can be clearly shown by PIV. Using fluorescent dye in the oil phase, jet fragmentation morphology can be captured simultaneously with PIV images.