Simulations on perturbation growth and mixing of a shocked light fluid layer with two different interfaces

The Richtmyer–Meshkov instability of a light fluid layer with two different interface modes is studied numerically. By fixing the wavelength of the second interface (I2) while varying that of the first interface (I1), we examine distinct cases with identical wavelengths at both interfaces, as well as smaller or larger wavelengths at I1, to explore the effects of initial layer configurations on instability development. The larger wavelength interface significantly transmits modes to the smaller wavelength interface, whereas mode transmission in the reverse direction is limited. This results in two primary consequences: (i) the smaller wavelength interface and the overall mixing layer evolve periodically with the larger wavelength; (ii) compared to the identical wavelength case, the linear amplitude growth duration of I2 is slightly extended for the smaller I1 wavelength case, but significantly prolonged for the larger I1 wavelength case. The linear amplitude growth rate of I2 for all cases can be predicted by the model of Jacobs et al. [J. Fluid Mech., vol. 195, 23–42 (1995)]. For cases with identical wavelengths and larger I1 wavelengths, the collisions of finger structures at both interfaces occur earlier, suppressing the growth of mixing width at early times while enhancing the mixed mass. In the later stages, the overall mixing efficiency in these cases significantly declines, despite continuous increases in both mixing width and mixed mass. This decline is attributed to severe deformation of the mixing layer due to interactions between finger structures, confining intense mixing to localized regions.