Pressure-Strain Interaction: I. On Compression, Deformation, and Implications For Pi-D

Abstract

The pressure-strain interaction describes the rate per unit volume that energy is converted between bulk flow and thermal energy in neutral fluids or plasmas. The term has been written as a sum of the pressure dilatation and the collisionless analogue of viscous heating referred to as $\mathrm{Pi}-\mathrm{D}$, which isolates the power density due to compressible and incompressible effects, respectively. It has been shown that $\mathrm{Pi}-\mathrm{D}$ can be negative, which makes its identification as collisionless viscous heating troubling. We argue that an alternate decomposition of pressure-strain interaction can be useful for interpreting the underlying physics. Since $\mathrm{Pi}-\mathrm{D}$ contains both normal deformation and shear deformation, we propose grouping the normal deformation with the pressure dilatation to describe the power density due to converging/diverging flows, with the balance describing the power density purely due to shear deformation. We then develop a kinetic theory interpretation of compression, normal deformation, and shear deformation. We use the results to determine the physical mechanisms that can make $\mathrm{Pi}-\mathrm{D}$ negative. We argue that both decompositions can be useful for the study of energy conversion in weakly collisional or collisionless fluids and plasmas, and implications are discussed.

16 pages, 4 figures, accepted to Physics of Plasmas

References in corpus (12)

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Cited by in corpus (5)

• Quantifying Energy Conversion in Higher Order Phase Space Density Moments in Plasmas
• Pressure-Strain Interaction: III. Particle-in-Cell Simulations of Magnetic Reconnection
• Pressure-Strain Interaction: II. Decomposition in Magnetic Field-Aligned Coordinates
• Higher-order nonequilibrium term: Effective power density quantifying evolution towards or away from local thermodynamic equilibrium
• HelioSwarm: A Multipoint, Multiscale Mission to Characterize Turbulence