Holographic flow visualization as a tool for studying three-dimensional coherent structures and instabilities

Abstract

Holography is capable of three-dimensional (3D) representation of spatial objects such as fluid interfaces and particle ensembles. Based on this, we adapt it into a 3D flow visualization tool called Holographic Flow Visualization (HFV). This technique provides a novel means of studying spatially and temporally evolving complex fluid flow structures marked by a disperse phase or interfaces of different fluids. This paper demonstrates that HFV is a straightforward technique, especially when the In-line Recording Off-axis Viewing (IROV) configuration is used. The technique can be applied either as a stand-alone experimental tool for studying scalar-based coherent structures, flow instabilities, interactions of different fluids driven by fluid dynamics, interfacial phenomena, or as a precursor to volumetric 3D velocity vector field measurement of complex transient flow dynamics. Experimental results in several complex fluid flows and flames demonstrate the effectiveness of HFV. Different methods are used to mark flow structures undergoing different instabilities: 1) a vortex ring grown out of a drop of polymer suspension falling in water, 2) cascade of a bag-shaped drop of milk in water, and 3) internal flow structures of a jet diffusion flame.

Laboratory experiments with tilted convective plumes on a centrifuge: a finite angle between the buoyancy force and the axis of rotation

“…First, blobs formed near the source owing to instability and wriggling motion of the incoming jet ( figure 3a). The dynamics of this process is poorly understood, but probably is somewhat similar to the instability of a drop of milk in a cup of coffee (Mollo-Christensen 1972; Meng et al 1998). Secondly, as the dyed fluid channelled along developing tilted Taylor 'ink walls' (or better to say 'tilted curtains') and accumulated at the lower end of the curtains (figure 3b), a blob formed which then descended at a somewhat steeper angle.…”

Tackling turbulence with Holographic Particle Image Velocimetry (HPIV)

“…Indeed, its optical simplicity makes it attractive for many applications including holographic 3D flow visualization, and hence it is one of the major HPIV techniques this lab is currently pursuing. 16,17 More remarkably, owing to the lower spatial resolution compared to off-axis holography, IROV is a promising framework for digital reconstruction, which the author believes to be the future wave of HPIV.…”

Preliminary Investigation of Three-Dimensional Flame Measurements with a Plenoptic Camera

“…Li and Ma [11] recently used similar tomographic techniques with an array of cameras to image turbulent reactive flows without any seeding by instead relying on the chemiluminescence of the flames. Meng et al [12] imaged a jet diffusion flame via holographic techniques, and Cho et al [13] used a 3D LIF technique to capture the combustion of droplets.…”