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 μm, 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 1.06×10⁵. 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.