Experiments on the Richtmyer-Meshkov instability of two nearby interfaces

The Ricthmyer-Meshkov instability of two nearby interfaces separating three gases of differing densities is studied experimentally in a vertical shock tube. The two interfaces are formed in the shock tube test section using opposed gas flows where the heaviest of the three gases (SF6) enters at the bottom of the test section and flows upward and the lightest gas (either air or helium) enters at the top of the driven section and flows downward. The intermediate gas (either air or CO2) enters the test section through porous metal plates forming an intermediate layer with 50 mm thickness. All three gases exit the shock tube through small holes at the interface locations, leaving two flat, stable interfaces separating the three gases. A nearly 2-dimensional, sinusoidal initial perturbation is given the lower interface by oscillating the shock tube in the lateral direction to produce a standing wave. A shock wave is generated by puncturing a polypropylene diaphragm that then travels downward in the shock tube where it impacts the fluid layer to produce the instability. The gas layer is visualized using time-resolved, planar Mie scattering. Measurements of the growth in perturbation amplitude are obtained and compared with equivalent single-interface configurations.