Experimental investigation of Rayleigh-Taylor mixing in gases using simultaneous PIV-PLIF

Dynamics of Rayleigh-Taylor (RT) mixing is studied using statistically stationary experiments performed in a multi-layer gas tunnel. The density ratio of air and air-helium-nitrogen mixture used results in an Atwood number (A) 0.13. Two types of diagnostics - particle image velocimetry (PIV) and planar laser induced fluorescence (PLIF) - are employed to obtain mixing width and simultaneous velocity-density data. PLIF using acetone is implemented for the first time for convective-type (flowing) statistically stationary RT experiments with gases. Velocity and density statistics, and their correlations (u^' ,v^' ,ρ^' ,ρ^'v^') are presented. As Atwood number for current experiments exceeds the widely accepted A 0.1 limit for Boussinesq approximation, non-Boussinesq-ness and anisotropy effects at this Atwood number are evaluated using metrics like higher-order moments (skewness, kurtosis) and anisotropy tensor. Results from current experiments are compared with existing turbulent RT mixing models (like BHR models).