Energy transfer across scales in laser-driven turbulence

We investigate the kinetic energy (KE) pathways in high-energy-density turbulence by applying the coarse graining approach to decompose scales. Using the FLASH code, we simulate a turbulent jet ablated from an aluminum cone target in both 2D and in 3D, following the configuration by Liao et al. [1]. The KE transfer across scales includes two processes: (i) deformation work, Π, which transfers energy due to multiscale velocity and determines the cascade in constant-density turbulence, and (ii) baropycnal work, Λ, which transfers energy due to pressure and density variations. We show that in both 2D and 3D, the strong shocks and high compressibility levels in our flows lead to a downscale transfer by deformation work, Π, and an upscale transfer by baropycnal work, Λ. However, marked differences between 2D and 3D become apparent when we restrict the analysis to the divergence-free part of the flow, where we find that Π transfers energy upscale in 2D, unlike in 3D. This contributes to the 2D turbulent jet to be more energetic at large scales and to travel faster relative to 3D.

[1] Liao A. S., et al., 2019, Physics of Plasmas, 26, 032306