Large-scale flow effects, energy transfer, and self-similarity on turbulence

Mininni, Pablo D.; Alexakis, Alexandros; Pouquet, A.

doi:10.1103/physreve.74.016303

Cited by 107 publications

(139 citation statements)

References 66 publications

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“…The solenoidal contribution to the interface (2 km s −1 ) would exceed the possible compressive one (≤2 km s −1 ), in agreement with Federrath et al (2009), who found that our observed statistical properties of turbulence in the Polaris Flare are in good agreement with solenoidal forcing on large scales. This result is similar to the findings of Mininni et al (2006a) that the stronger the shear on large scales, the more intense the intermittency of velocity increments on small scales.…”

Section: What Is the Nature Of The Interface?supporting

confidence: 82%

“…Because it is supersonic, magnetized, and develops in a multiphase medium, interstellar turbulence is expected to differ from turbulence in laboratory flow experiments or in state-of-the-art numerical simulations, e.g., Chanal et al (2000) for experiments in gaseous helium and Mininni et al (2006a) or Alexakis et al (2007) for MHD simulations. Nonetheless, it may carry some universal properties of turbulence, such as space-time intermittency (for a review see Anselmet et al 2001).…”

Section: Introductionmentioning

confidence: 99%

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Intermittency of interstellar turbulence: parsec-scale coherent structure of intense, velocity shear

Hily-Blant¹,

Falgarone

2009

A&A

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Aims. Benefitting from the duality of turbulence (random versus coherent motions), we search for coherent structures in the turbulent velocity field of molecular clouds, anticipating their importance in cloud evolution. Methods. We analyse a large map (40 by 20 ) obtained with the HERA multibeam receiver (IRAM-30 m telescope) in a high latitude cloud of the Polaris Flare at unprecedented spatial (11 ) and spectral (0.05 km s −1 ) resolution for the 12 CO(2−1) line. Results. We find that two parsec-scale components of velocities differing by ∼2 km s −1 , share a narrow interface (<0.15 pc) that appears to be an elongated structure of intense velocity-shear, ∼15 to 30 km s −1 pc −1 . The locus of the extrema of line-centroidvelocity increments (E-CVI) in that field follows this intense-shear structure as well as that of the 12 CO(2−1) high-velocity line wings. The tiny spatial overlap in projection of the two parsec-scale components implies that they are sheets of CO emission and that discontinuities in the gas properties (CO enrichment and/or increase in gas density) occur at the position of the intense velocity shear. Conclusions. These results identify spatial and kinematic coherence on scales of between 0.03 pc and 1 pc. They confirm that the departure from Gaussianity of the probability density functions of E-CVIs is a powerful statistical tracer of the intermittency of turbulence. They provide support for a link between large-scale turbulence, its intermittent dissipation rate and low-mass dense core formation.

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Section: What Is the Nature Of The Interface?supporting

confidence: 82%

Section: Introductionmentioning

confidence: 99%

Intermittency of interstellar turbulence: parsec-scale coherent structure of intense, velocity shear

Hily-Blant¹,

Falgarone

2009

A&A

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“…However, the T ± (K, Q) transfer functions do not give us direct information on the scales of the two fields z + and z − that interact and contribute to the energy cascade. To investigate the locality on nonlocality of the interactions between the two Elsässer counterpropagating waves, we introduce the partial fluxes (see [28,29]) defined as:…”

Section: Definitionsmentioning

confidence: 99%

Anisotropic fluxes and nonlocal interactions in magnetohydrodynamic turbulence

et al. 2007

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We investigate the locality or nonlocality of the energy transfer and of the spectral interactions involved in the cascade for decaying magnetohydrodynamic (MHD) flows in the presence of a uniform magnetic field B at various intensities. The results are based on a detailed analysis of threedimensional numerical flows at moderate Reynold numbers. The energy transfer functions, as well as the global and partial fluxes, are examined by means of different geometrical wavenumber shells. On the one hand, the transfer functions of the two conserved Elsässer energies E + and E − are found local in both the directions parallel (k -direction) and perpendicular (k ⊥ -direction) to the magnetic guide-field, whatever the B-strength. On the other hand, from the flux analysis, the interactions between the two counterpropagating Elsässer waves become nonlocal. Indeed, as the B-intensity is increased, local interactions are strongly decreased and the interactions with small k modes dominate the cascade. Most of the energy flux in the k ⊥ -direction is due to modes in the plane at k = 0, while the weaker cascade in the k -direction is due to the modes with k = 1. The stronger magnetized flows tends thus to get closer to the weak turbulence limit where the three-wave resonant interactions are dominating. Hence, the transition from the strong to the weak turbulence regime occurs by reducing the number of effective modes in the energy cascade.

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“…Recently, MJ04 found that intense structures of vorticity and rate of strain are respectively filaments and ribbons that are not randomly distributed in space but that instead form clusters of inertial-range extent, implying a large-scale organization of the small-scale intermittent structures. In 1024 3 numerical simulations of incompressible turbulence, with variable large-scale stirring forces, Mininni et al (2006a) have shown that the large and small-scale properties of the flow are correlated, namely that i) more intense small-scale gradients and vortex tubes are concentrated in the regions where the large-scale shears are the largest, and that ii) the departure from the Kolmogorov scaling is more pronounced in these regions. They infer from these results that the statistical signatures of intermittency are linked to the existence of the small-scale vortex tubes.…”

Section: Introductionmentioning

confidence: 99%

Dissipative structures of diffuse molecular gas

Hily-Blant

Falgarone

Pety

2008

A&A

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Aims. We further characterize the structures tentatively identified on thermal and chemical grounds as the sites of dissipation of turbulence in molecular clouds (Papers I and II). Methods. Our study is based on two-point statistics of line centroid velocities (CV), computed from three large 12 CO maps of two fields. We build the probability density functions (PDF) of the CO line centroid velocity increments (CVI) over lags varying by an order of magnitude. Structure functions of the line CV are computed up to the 6th order. We compare these statistical properties in two translucent parsec-scale fields embedded in different large-scale environments, one far from virial balance and the other virialized. We also address their scale dependence in the former, more turbulent, field. Results. The statistical properties of the line CV bear the three signatures of intermittency in a turbulent velocity field: (1) the nonGaussian tails in the CVI PDF grow as the lag decreases, (2) the departure from Kolmogorov scaling of the high-order structure functions is more pronounced in the more turbulent field, (3) the positions contributing to the CVI PDF tails delineate narrow filamentary structures (thickness ∼0.02 pc), uncorrelated to dense gas structures and spatially coherent with thicker ones (∼0.18 pc) observed on larger scales. We show that the largest CVI trace sharp variations of the extreme CO linewings and that they actually capture properties of the underlying velocity field, uncontaminated by density fluctuations. The confrontation with theoretical predictions leads us to identify these small-scale filamentary structures with extrema of velocity-shears. We estimate that viscous dissipation at the 0.02 pc-scale in these structures is up to 10 times higher than average, consistent with their being associated with gas warmer than the bulk. Last, their average direction is parallel (or close) to that of the local magnetic field projection. Conclusions. Turbulence in these translucent fields exhibits the statistical and structural signatures of small-scale and inertial-range intermittency. The more turbulent field on the 30 pc-scale is also the more intermittent on small scales. The small-scale intermittent structures coincide with those formerly identified as sites of enhanced dissipation. They are organized into parsec-scale coherent structures, coupling a broad range of scales.

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Large-scale flow effects, energy transfer, and self-similarity on turbulence

Cited by 107 publications

References 66 publications

Intermittency of interstellar turbulence: parsec-scale coherent structure of intense, velocity shear

Intermittency of interstellar turbulence: parsec-scale coherent structure of intense, velocity shear

Anisotropic fluxes and nonlocal interactions in magnetohydrodynamic turbulence

Dissipative structures of diffuse molecular gas

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