Strong-Shock Interface Interactions
Ravi Samtaney, NASA Ames Research Center
Daniel I. Meiron, California Institute of Technology

The interaction of a shock wave with a contact discontinuity, e.g. an interface separating two gases, is an important problem in compressible hydrodynamics. Studies of shock-contact interactions are motivated by a desire to understand turbulent mixing in supersonic combustion ramjets where mixing is desirable, in inertial confinement fusion where mixing inhibits fusion, and in astrophysical phenomenon such as supernovae.

The goal of the Center for Simulation of Dynamic Response of Materials at Caltech is to construct a virtual shock physics facility in which the full three-dimensional response of a variety of target materials can be computed for a wide range of compressive, tensional, and shear loadings, including those loadings produced by detonation of energetic materials. As part of that Center's activities, Dr. Samtaney has been collaborating with Prof. Meiron to further our understanding of this "re-shock" problem. Dr. Samtaney is currently carrying out his calculations on all 512 application processors of the CRAY T3E at the Pittsburgh Supercomputing Center , where he is working closely with Dr. Nick Nystrom to optimize his utilization of computational resources.

The physical picture is characterized by a shock wave propagating from left to right in a gas. Upon striking the interface the shock wave splits into a reflected wave and a transmitted shock, which moves into the gas of different density. The main parameters of interest are the speed of the incident shock, the ratio of densities of the two gases, the specific heat ratio of the two gases, and the geometry of the interface. The focus of the present study is to investigate the effect of a strong shock moving from a light to a heavy gas. The present study is a continuation of the work of Samtaney and Meiron, wherein they examined strong shock-contact interactions in two dimensions. Furthermore, the current study is a precursor to planned experiments in the hypervelocity shock tunnel "T5" at Caltech.

The figures show the density before (1a-c) and after (2a-c) the transmitted shock is allowed to reflect from the right side boundary and re-shock the interface. The re-shock causes the interface to become much more convoluted, which is advantageous for mixing. Including sufficient detail to obtaining correct results requires very large computational resources: this three-dimensional calculation involves 16 million grid points and evolves through 19,200 time steps. Related calculations will use a grid twice as dense in each dimension, resulting in 128 million grid points.

Ongoing work at PSC is increasing the resolution and time scale of these simulations to further explore re-shock phenomena as well as other aspects of compressible turbulence vital to the ASCI mission.