A novel approach is presented to simultaneously measure volume fraction (using two-tracer planar laser induced fluorescence (PLIF)) and velocity (using particle image velocimetry (PIV)) to study three-component mixing in the multilayer Rayleigh–Taylor instability, constituting of three layers in a blow-down gas tunnel. This approach enables non-intrusive, planar measurements of each of the three components in the mixture. By using acetone and anisole as PLIF tracers and a three-camera system, each tracer’s fluorescence is captured alongside scattered light from PIV particles. Key considerations for two-tracer PLIF with acetone and anisole are discussed, including spectral conflicts as well as the independence of anisole fluorescence from the presence of acetone, and vice-versa. The diagnostic is first validated and then applied to the Rayleigh–Taylor instability in a three-layer configuration, yielding previously unattainable results. This includes simultaneous volume fraction profiles, the covariances between the volume fraction fluctuations of different layers, as well as each layer’s covariance between their respective volume fraction and vertical velocity fluctuations. Such quantities are crucial for the development and validation of variable density turbulence models. The presented diagnostic is extendable to other three-component gas mixing experiments with small pressure variations, provided that the tracer volume fractions remain small.
Dzurny et al. (Sun,) studied this question.