The effect of initial conditions on the growth of Richtmyer–Meshkov instability

The baroclinic generation of vorticity at a stratified interface when subjected to a shock-wave occurs in a process known as the Richtmyer–Meshkov instability. This study investigates the growth of single-mode sinusoidal perturbations on an air/sulfur hexafluoride (SF₆) interface by this process using a 7m tall vertical shock tube (1.2 Ma). The perturbations are induced by subjecting the interface to an undulating cross-flow structure produced by steady-state oscillations of a symmetrical motorized airfoil flapper in the cross-stream. For various flapper frequencies and sweeping angles employed, both the initial perturbation wavelength (λ₀) and amplitude (η₀) produced are noted to affect the late-time growth rates, significantly. The perturbation amplitude (η) follows a power-law dependence with downstream distance and can be collapsed for all flapper conditions by a dimensional-scaling k(η/ η₀) = 0.21(kx)^0.44 . Turbulent statistics of the mixing region in addition to vortex identification and swirl strength within are also investigated for obtaining correlations with the flapper oscillation characteristics.