Abstract
An optical system combining phase-shifting interferometry (PSI) and particle image velocimetry (PIV) is built and verified with simultaneous two-dimensional temperature- and velocity-field measurements of a convective flow. The well-known Rayleigh-B\'enard convection in laminar regime in a cubical cavity filled with water is chosen as the experimental validation case. Three-, four-, and six-bucket temporal phase-shifting equations using a rotating polarizer method are tuned under different light-source power conditions, first without PIV, to produce high-resolution phase-shifted data. The results showed that the three-bucket phase-shifting equation is the most robust method over a wide range of laser powers, while the PIV tracers decreased the PSI precision from 1.5% in the case without tracers to 3.0% when seeded at 0.02 wt%. The temporal and spatial resolution of the PSI measurement is 0.1 s and 6.47 $\ensuremath{\mu}\mathrm{m}$, respectively. Owing to the combined PSI and PIV technique, both temperature and velocity characteristics are obtained, unveiling the existence of several flow bifurcations as the Rayleigh number is increased up to $1.06\ifmmode\times\else\texttimes\fi{}{10}^{5}$. This optical setup is a potential paradigm shift in heat- and fluid-flow visualization, while having a great potential in biosensor development for concurrent velocity-, concentration-, and temperature-field measurements of aerosols and flows with multicomponent species.
Highlights
Buoyant flows are ubiquitous in nature [1,2] and engineered systems (e.g., [3,4,5])
The results showed that the three-bucket phase-shifting equation is the most robust method over a wide range of laser powers, while the particle image velocimetry (PIV) tracers decreased the phase-shifting interferometry (PSI) precision from 1.5% in the case without tracers to 3.0% when seeded at 0.02 wt%
Despite convection entailing the concurrent transport of both momentum and energy, most of the experimental visualization techniques developed so far focus on either heat and mass or fluid flow, represented by temperature and concentration and velocity fields, respectively
Summary
Buoyant flows are ubiquitous in nature [1,2] and engineered systems (e.g., [3,4,5]). The physics of thermal plumes in buoyant flows has long been one of the central research questions in the fluid mechanics and geophysics communities, owing to its paramount role in convective heat and mass transport phenomena (e.g., [6,7,8,9]). A major challenge that limits the exploration of buoyant flows is the lack of experimental diagnostics for simultaneous, high-resolution, and noninvasive temperature- and velocity-field measurements. We propose a hybrid optical system in which phase-shifting interferometry (PSI) and particle image velocimetry (PIV) are employed to perform concurrent temperature- and velocity-field measurements. PSI and PIV are well-established techniques to measure temperature [10] and velocity [11] fields, respectively, but have never been used to determine both flow fields instantaneously. High-accuracy measurements are generally limited to either velocity [12] or temperature [13] fields. Another common approach is to complement limited experimental data to validate numerical
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