Particle image velocimetry in a variable density flow: application to a dynamically evolving microburst

Abstract

A fundamental difficulty in the experimental study of gravity-driven flows using particle image velocimetry (PIV) and other optical diagnostic techniques is the problem associated with variations in the refractive index within the fluid. This paper discusses a method by which the refractive indices of two fluids are matched while maintaining density differences of up to 4%-Aqueous solutions of glycerol and potassium phosphate are used to achieve precise index matching in the presence of mixed and unmixed constituents. The effectiveness of the method is verified in a PIV study of a laboratory-scale model of an atmospheric microburst where planes of two-dimensional velocity vectors are obtained in the evoiving flow field.

Refractive-index and density matching in concentrated particle suspensions: a review

“…Hopkins et al (2000) characterized the flow into an optically transparent nasal cavity and Budwig (1994), Gijsen et al (1996) and Nguyen et al (2004) the flow in arteries. Alahyari and Longmire (1994), Atsavapranee and Gharib (1997), Augier et al (2003), Daviero et al (2001), Hannoun et al (1988) and McDougall (1979) used two sets of immiscible refractive-index-matched fluids to measure into density-stratified flows.…”

Scaling for turbulent viscosity of buoyant plumes in stratified fluids: PIV measurement with implications for submarine hydrothermal plume turbulence

“…where κ3 (Alahyari and Longmire, 1994;Daviero et al, 2001;Horner-Devine, 2006). However, the present study did not take any measure to match the index of refraction in the fluid.…”

A review of solid–fluid selection options for optical-based measurements in single-phase liquid, two-phase liquid–liquid and multiphase solid–liquid flows

“…Miscible liquid-liquid RIM systems, which are considered single-phase flows here, are of interest, for instance when studying the mixing or multicomponent, density stratified flows (Hannoun 1985;Hannoun et al 1988;De Silva and Fernando 1998;Daviero et al 2001) or gravity-induced flows (McDougall 1979;Longmire 1994, 1997). The miscible liquids can be RI matched and the density can be tuned separately, for example, Alahyari and Longmire (1994) used two aqueous solutions (potassium dihydrogen phosphate (KH 2 PO 4 ) and glycerol) to create a density difference of 4% in the RIM fluids. Similarly, beyond RI matching, it may be desirable to match also the viscosity of the liquids to set the Reynolds number or, alternatively, to introduce controlled viscosity variations that would be exhibited in processes such as the mixing of miscible systems.…”