Proposed mechanism describes the transition to turbulent flow in shocked heavy gases

Shock waves that impact heavy gases are important in a variety of applications, including inertial confinement fusion. In this case, high pressures and temperatures create imperfect and uneven material interfaces. Shock waves propagate these surface defects through the gas to create an initial flow, and secondary shocks can disrupt the flow to cause turbulence, which can be detrimental to the application.

New research in Physics of Fluids attempts to understand these phenomena from a fundamental level by using direct numerical simulations based on the high resolution finite-volume methods. The model considers a heavy gas in a rectangular tube separated from air by a sinusoidal thin film. An initial shock disrupts the heavy gas, creating a waveform initiated in the shape of the thin film, while generating instability in the gas that causes vortices in the flow. As the shock reflects off the end of the tube and returns through the gas, the instability is enhanced and turbulent mixing is observed.

The bulk of this work is intended to understand the time dynamics from shock initiation to turbulence generation. While previous studies focused on turbulent behavior from shock phenomena, the authors here developed a deeper understanding of the actual mixing process.

They propose a new mechanism for the mixing state using a subgrid scale energy transfer, causing forward and backward energy scattering at developed vortices during the transition to turbulence. Collisions of these vortices produce a spreading of the dissipated energy in three dimensions causing smaller scale structures, which destroy the two-dimensional flow from the initial shock. These results help identify a new fundamental mechanism of shock-related flow and turbulent mixing in heavy gases.

Source: “Turbulent mixing and energy transfer of reshocked heavy gas curtain,” by Wei-Gang Zeng, Jian-Hua Pan, Yu-Tao Sun, and Yu-Xin Ren, Physics of Fluids (2018). The article can be accessed at https://doi.org/10.1063/1.5032275 .