pike and vortex formation in an

We present an experimental and numerical study of a complex flow that develops upon impulsive (shock) acceleration of a compressible multiphase medium. In the initial conditions, both diffuse density interfaces (gas-gas) and sharp density interfaces (gas-fluid) are present, with the fluid phase embedded within the gas in the form of small droplets. Our initial experiments failed to reveal some features prominent in the numerical simulations. For such occurrences, it is common practice to look for problems with the computational model or its implementation. In the case we present, however, the fault lay with a visualization technique that relied exclusively on visible-light Mie scattering from the droplets. A different visualization technique (laser-induced fluorescence) reveals that droplets do not follow some of the flow features forming after acceleration. The experiments and numerics we present cover Mach numbers ranging from 1.2 to 2.1, with characteristic Atwood number (dimensionless density ratio) of 0.5.