Optical Method for Simultaneous High-Resolution Measurement of Heat and Fluid Flow: The Case of Rayleigh-Bénard Convection

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.