arXiv subjects

De-Jun Sun

Publications and source records attributed to De-Jun Sun.

3 recordsLinked to original sources

arXiv2024

Self-generated magnetic field in three-dimensional ablative Rayleigh-Taylor instability

The self-generated magnetic field in three-dimensional (3D) single-mode ablative Rayleigh-Taylor instabilities (ARTI) relevant to the acceleration phase of a direct-drive inertial confinement fusion (ICF) implosion is investigated. It is found that stronger magnetic fields up to a few thousands of T can be generated by 3D ARTI than by its two-dimensional (2D) counterpart. The Nernst effects significantly alter the magnetic fields convection and amplify the magnetic fields. The scaling law for the magnetic flux obtained in the 2D simulations performs reasonably well in the 3D cases. While the magnetic field significantly accelerates the bubble growth in the short-wavelength 2D modes through modifying the heat fluxes, the magnetic field mostly accelerates the spike growth but has little influence on the bubble growth in 3D ARTI.

physics.plasm-ph↗

arXiv2019

Penetrative turbulent Rayleigh-Bénard convection in two and three dimensions

Penetrative turbulent Rayleigh-Bénard convection which depends on the density maximum of water near $4^\circ\rm{C}$ is studied using two-dimensional (2D) and three-dimensional (3D) direct numerical simulations (DNS). The working fluid is water near $4^\circ\rm{C}$ with Prandtl number $Pr=11.57$. The considered Rayleigh numbers $Ra$ range from $10^7$ to $10^{10}$. The density inversion parameter $θ_m$ varies from 0 to 0.9. It is found that the ratio of the top and bottom thermal boundary-layer thickness ($F_λ=λ_t^θ/λ_b^θ$) increases with increasing $θ_m$, and the relationship between $F_λ$ and $θ_m$ seems to be independent of $Ra$. The centre temperature $θ_c$ is enhanced compared to that of Oberbeck-Boussinesq (OB) cases, as $θ_c$ is related to $F_λ$ with $1/θ_c=1/F_λ+1$, $θ_c$ is also found to have a universal relationship with $θ_m$ which is independent of $Ra$. Both the Nusselt number $Nu$ and the Reynolds number $Re$ decrease with increasing $θ_m$, the normalized Nusselt number $Nu(θ_m)/Nu(0)$ and Reynolds number $Re(θ_m)/Re(0)$ also have universal relationships with $θ_m$ which seem to be independent of both $Ra$ and the aspect ratio $Γ$. The scaling exponents of $Nu\sim Ra^α$ and $Re\sim Ra^β$ are found to be insensitive to $θ_m$ despite of the remarkable change of the flow organizations.

physics.flu-dyn↗

arXiv2008

Onset of unsteady horizontal convection in rectangle tank at $Pr=1$

The horizontal convection within a rectangle tank is numerically simulated. The flow is found to be unsteady at high Rayleigh numbers. There is a Hopf bifurcation of $Ra$ from steady solutions to periodic solutions, and the critical Rayleigh number $Ra_c$ is obtained as $Ra_c=5.5377\times 10^8$ for the middle plume forcing at $Pr=1$, which is much larger than the formerly obtained value. Besides, the unstable perturbations are always generated from the central jet, which implies that the onset of instability is due to velocity shear (shear instability) other than thermally dynamics (thermal instability). Finally, Paparella and Young's [J. Fluid Mech. 466 (2002) 205] first hypotheses about the destabilization of the flow is numerically proved, i.e. the middle plume forcing can lead to a destabilization of the flow.

physics.flu-dyn↗