Investigation of grid generated turbulence and initial conditions on the multilayer Rayleigh-Taylor instability

The influence of grid-generated turbulence on Rayleigh–Taylor instability (RTI) is investigated in a multi-layered gas tunnel. Experiments are conducted in a statistically stationary, blow-down, three-layer gas tunnel, where the top and bottom layers are dense air streams, and the middle layer is a lighter air–helium mixture. This configuration creates a three-layer stratification with an upper RTI-unstable interface and a lower RTI-stable interface. Classic grids made from sheet-metal are placed upstream to introduce controlled turbulence, adding 1%–10% kinetic energy to each stream. Simultaneous particle image velocimetry (PIV) and two-tracer planar laser-induced fluorescence (PLIF) are used to resolve velocity fields and volume fractions. Data are presented for Atwood numbers from 0.25 to 0.6. The two-tracer PLIF allows detailed quantification of mixing between layers via molecular mixedness and other scalar metrics. The interplay between interfacial dynamics and the turbulent velocity field is explored. These measurements support the development and validation of turbulence models in variable-density flow regimes.