Richtmyer-Meshkov instability occurs whenever a shock wave passes over a nearly planar interface separating two fluids of unequal density. It is one of the most fundamental fluid instabilities and is of importance to applications ranging from astrophysics to supersonic combustion.

 

Previous experimental studies have been hampered by the difficulty in generating a well-defined interface between two gases. We have overcome this difficulty by utilizing a counter-flow system in which a light gas (Air) and a heavy gas (SF6) flow from opposite ends of the driven section of a vertical shock tube. The gases meet and are allowed to exit the tube through slots in the shock tube wall thus forming a stagnation point flow at the interface location.

 

The instability is initiated by the interaction of an M = 1.2 incident shock wave.  A random three-dimensional perturbation is then imposed on the otherwise flat interface by oscillating the column of gas in the vertical direction using two loudspeakers located at the top and bottom of the driven section.

 

We study the turbulent mixing layer that develops at the interface as a result of initial shock-interface interaction. The flow is visualized using planar Mie scattering in which light from a laser sheet is scattered by smoke particles seeded in the air and captured using high-speed CMOS video cameras. Experiments reveal a distribution of growth behaviors ranging from linear growth with a nearly constant growth rate to highly nonlinear growth with a growth rate that strongly decreases with time.