Inviscid criterion for decomposing scales

Zhao, Dongxiao; Aluie, Hussein

doi:10.1103/physrevfluids.3.054603

Cited by 43 publications

(32 citation statements)

References 55 publications

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“…The numerical simulations are conducted with the DiNuSUR code which has been used in many previous studies (e.g. [50,41,51,52]). We use sixth-order compact finite differences [53] in the vertical direction and pseudo-spectral method in the horizontal direction, similar to previous RTI DNS in the variable density limit [54,55].…”

Section: Governing Equationsmentioning

confidence: 99%

Revisiting the late-time growth of single-mode Rayleigh–Taylor instability and the role of vorticity

Bian

Aluie

Zhao

et al. 2020

Physica D: Nonlinear Phenomena

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Growth of the single-fluid single-mode Rayleigh-Taylor instability (RTI) is revisited in 2D and 3D using fully compressible high-resolution simulations. We conduct a systematic analysis of the effects of perturbation Reynolds number (Re p ) and Atwood number (A) on RTI's late-time growth. Contrary to the common belief that single-mode RTI reaches a terminal bubble velocity, we show that the bubble re-accelerates when Re p is sufficiently large, consistent with [Ramaparabhu et al. 2006, Wei andLivescu 2012]. However, unlike in [Ramaparabhu et al. 2006], we find that for a sufficiently high Re p , the bubble's late-time acceleration is persistent and does not vanish. Analysis of vorticity dynamics shows a clear correlation between vortices inside the bubble and re-acceleration. Due to symmetry around the bubble and spike (vertical) axes, the self-propagation velocity of vortices points in the vertical direction. If viscosity is sufficiently small, the vortices persist long enough to enter the bubble tip and accelerate the bubble [Wei and Livescu 2012]. A similar effect has also been observed in ablative RTI [Betti and Sanz 2006]. As the spike growth increases relative to that of the bubble at higher A, vorticity production shifts downward, away from the centerline and toward the spike tip. We modify the Betti-Sanz model for bubble velocity by introducing a vorticity efficiency factor η = 0.45 to accurately account for re-acceleration caused by vorticity in the bubble tip. It had been previously suggested that vorticity generation and the associated bubble re-acceleration are suppressed at high A. However, we present evidence that if the large Re p limit is taken first, bubble re-acceleration is still possible. Our results also show that re-acceleration is much easier to occur in 3D than 2D, requiring smaller Re p thresholds.

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Section: Governing Equationsmentioning

confidence: 99%

Revisiting the late-time growth of single-mode Rayleigh–Taylor instability and the role of vorticity

Bian

Aluie

Zhao

et al. 2020

Physica D: Nonlinear Phenomena

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“…To study the energy spectrum in variable-density or compressible turbulence, it is common to decompose the energy as | √ ρu| 2 or | √ ρu | 2 [56,[66][67][68]. However, it is pointed out by Zhao and Aluie [69] that one cannot prove spectral locality using energy definitions of the form | √ ρu| 2 , because the corresponding transport equations contain terms FIG. 24.…”

Section: E Probability Density Functions Of Mole Fractionmentioning

confidence: 99%

High-resolution Navier-Stokes simulations of Richtmyer-Meshkov instability with reshock

2019

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The interaction of a Mach 1.45 shock wave with a perturbed planar interface between sulphur hexafluoride and air is studied through high-resolution two-dimensional (2D) and three-dimensional (3D) shock-capturing adaptive mesh refinement simulations of multi-species Navier-Stokes equations. The sensitivities of time-dependent statistics on grid resolution for 2D and 3D simulations are evaluated to ensure the accuracy of the results. The numerical results are used to examine the differences between the development of 2D and 3D Richtmyer-Meshkov instability during two different stages: (1) initial growth of hydrodynamic instability from multi-mode perturbations after first shock and (2) transition to chaotic or turbulent state after re-shock. The effects of the Reynolds number on the mixing in 3D simulations are also studied through varying the transport coefficients. * wongml@stanford.edu † livescu@lanl.gov ‡

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“…The kinetic and internal energy spectra are calculated based on the Fourier transforms of √ ρu and √ ρcs. While this choice theoretically violates the inviscid criterion for decomposing scales for variable density flows(Zhao & Aluie 2018), we expect no practical differences for our simulations given the limited density variations in the subsonic regime.…”

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confidence: 98%

As a Matter of State: The Role of Thermodynamics in Magnetohydrodynamic Turbulence

Grete

O’Shea

Beckwith

2020

ApJ

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Turbulence simulations play a key role in advancing the general understanding of the physical properties turbulence and in interpreting astrophysical observations of turbulent plasmas. For the sake of simplicity, however, turbulence simulations are often conducted in the isothermal limit. Given that the majority of astrophysical systems are not governed by isothermal dynamics, we aim to quantify the impact of thermodynamics on the physics of turbulence, through varying adiabatic index, γ, combined with a range of optically thin cooling functions. In this paper, we present a suite of ideal magnetohydrodynamics simulations of thermally balanced stationary turbulence in the subsonic, super-Alfvénic, high β p (ratio of thermal to magnetic pressure) regime, where turbulent dissipation is balanced by two idealized cooling functions (approximating linear cooling and free-free emission) and examine the impact of the equation of state by considering cases that correspond to isothermal, monatomic and diatomic gases. We find a strong anticorrelation between thermal and magnetic pressure independent of thermodynamics, whereas the strong anticorrelation between density and magnetic field found in the isothermal case weakens with increasing γ. Similarly, with the linear relation between variations in density and thermal pressure with sonic Mach number becomes steeper with increasing γ. This suggests that there exists a degeneracy in these relations with respect to thermodynamics and Mach number in this regime, which is dominated by slow magnetosonic modes. These results have implications for attempts to infer (e.g.) Mach numbers from (e.g.) Faraday rotation measurements, without additional information regarding the thermodynamics of the plasma. However, our results suggest that this degeneracy can be broken by utilizing higher-order moments of observable distribution functions.

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Inviscid criterion for decomposing scales

Cited by 43 publications

References 55 publications

Revisiting the late-time growth of single-mode Rayleigh–Taylor instability and the role of vorticity

Revisiting the late-time growth of single-mode Rayleigh–Taylor instability and the role of vorticity

High-resolution Navier-Stokes simulations of Richtmyer-Meshkov instability with reshock

As a Matter of State: The Role of Thermodynamics in Magnetohydrodynamic Turbulence

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