Evolution of a shocked multimode interface with sharp corners

Richtmyer-Meshkov instability of an inverse-chevron air/SF6 interface subjected to a weak shock wave is experimentally studied. The inverse-chevron interface is a typical configuration that possesses multimode features and sharp corners. Using the soap film technique, five inverse-chevron interfaces with different initial vertex angles are generated to highlight the effects of initial amplitude-wavelength ratio on flow characteristics. A high-speed Schlieren system is used to observe the postshock flow field. After shock impact, a vortex pair is derived from the upstream interface, and the scale of the vortex pair is sensitive to the initial amplitude-wavelength ratio. The width growth in the linear phase is measured and compared with the classical impulsive model and a modified model considering a velocity reduction factor, and the latter is proven to be effective for moderate to large initial amplitudes. The linear growth rate is also a nonmonotone function of the amplitude-wavelength ratio. Further comparison with our previous work illustrates that the amplitude-wavelength ratio corresponding to the maximum width growth rate is associated with the Atwood number, which is consistent with the previous numerical results. A weakly nonlinear growth is observed at late stages, which deviates from the predictions of most typical nonlinear models. Finally, an empirical model is proposed that provides a satisfactory prediction of width growth in linear and weakly nonlinear stages.