Rarefaction-induced Rayleigh–Taylor growth for a light gas layer

The Rayleigh–Taylor (RT) interface evolution within a light fluid layer subjected to rarefaction-driven flows is investigated through rarefaction-tube experiments and numerical simulations, with focus on initial condition effects. Rarefaction-induced acceleration yields distinct RT instability responses at the two interfaces: the upstream interface (I1) becomes RT-unstable while the downstream interface (I2) remains RT-stable. This contrast drives interface coupling that reduces perturbation growth for in-phase configurations but weakly suppresses or promotes growth for anti-phase configurations. To resolve these distinct behaviors, Mikaelian's linear model [Phys. Fluids, 7, 888–890 (1995)] is modified through incorporating a phase correction factor. The modified model accurately predicts linear amplitude evolution for both interfaces across layer widths, with validity further confirmed through comparison with prior heavy fluid layer results. Increasing I2's initial amplitude or reducing layer width modulates I1 growth, suppressing it for in-phase cases while amplifying it for anti-phase cases, where layer width reduction proves more effective. A higher Atwood number at I2 intensifies the reflected rarefaction wave, thereby reducing I1 growth; however, it simultaneously enhances interface coupling, enlarging the growth disparity at I1 between in-phase and anti-phase configurations. These findings provide insights for manipulating perturbation growth through tailored initial conditions.