Turbulent transport in a non-Markovian velocity field
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arXiv
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| Format: | Preprint |
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2025
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| _version_ | 1866929698779430912 |
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| author | Kishore, G. Singh, Nishant K. |
| author_facet | Kishore, G. Singh, Nishant K. |
| contents | The commonly used quasilinear approximation allows one to calculate the turbulent transport coefficients for the mean of a passive scalar or a magnetic field in a given velocity field. Formally, the quasilinear approximation is exact when the correlation time of the velocity field is zero. We calculate the lowest-order corrections to the transport coefficients due to the correlation time being nonzero. For this, we use the Furutsu-Novikov theorem, which allows one to express the turbulent transport coefficients in a Gaussian random velocity field as a series in the correlation time. We find that the turbulent diffusivities of both the mean passive scalar and the mean magnetic field are suppressed. Nevertheless, contradicting a previous study, we show that the turbulent diffusivity of the mean magnetic field is smaller than that of the mean passive scalar. We also find corrections to the $α$ effect. |
| format | Preprint |
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arxiv_https___arxiv_org_abs_2502_02946 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Turbulent transport in a non-Markovian velocity field Kishore, G. Singh, Nishant K. Fluid Dynamics Astrophysics of Galaxies Solar and Stellar Astrophysics The commonly used quasilinear approximation allows one to calculate the turbulent transport coefficients for the mean of a passive scalar or a magnetic field in a given velocity field. Formally, the quasilinear approximation is exact when the correlation time of the velocity field is zero. We calculate the lowest-order corrections to the transport coefficients due to the correlation time being nonzero. For this, we use the Furutsu-Novikov theorem, which allows one to express the turbulent transport coefficients in a Gaussian random velocity field as a series in the correlation time. We find that the turbulent diffusivities of both the mean passive scalar and the mean magnetic field are suppressed. Nevertheless, contradicting a previous study, we show that the turbulent diffusivity of the mean magnetic field is smaller than that of the mean passive scalar. We also find corrections to the $α$ effect. |
| title | Turbulent transport in a non-Markovian velocity field |
| topic | Fluid Dynamics Astrophysics of Galaxies Solar and Stellar Astrophysics |
| url | https://arxiv.org/abs/2502.02946 |