23 research outputs found
Fast Numerical simulations of 2D turbulence using a dynamic model for Subgrid Motions
We present numerical simulation of 2D turbulent flow using a new model for
the subgrid scales which are computed using a dynamic equation linking the
subgrid scales with the resolved velocity. This equation is not postulated, but
derived from the constitutive equations under the assumption that the
non-linear interactions of subgrid scales between themselves are equivalent to
a turbulent viscosity.The performances of our model are compared with Direct
Numerical Simulations of decaying and forced turbulence. For a same resolution,
numerical simulations using our model allow for a significant reduction of the
computational time (of the order of 100 in the case we consider), and allow the
achievement of significantly larger Reynolds number than the direct method.Comment: 35 pages, 9 figure
Scaling laws and vortex profiles in 2D decaying turbulence
We use high resolution numerical simulations over several hundred of turnover
times to study the influence of small scale dissipation onto vortex statistics
in 2D decaying turbulence. A self-similar scaling regime is detected when the
scaling laws are expressed in units of mean vorticity and integral scale, as
predicted by Carnevale et al., and it is observed that viscous effects spoil
this scaling regime. This scaling regime shows some trends toward that of the
Kirchhoff model, for which a recent theory predicts a decay exponent .
In terms of scaled variables, the vortices have a similar profile close to a
Fermi-Dirac distribution.Comment: 4 Latex pages and 4 figures. Submitted to Phys. Rev. Let
A Comparison of Time Discretization Schemes for Two-Timescale Problems in Geophysical Fluid Dynamics
Bridging the condensation–collision size gap: a direct numerical simulation of continuous droplet growth in turbulent clouds
In most previous direct numerical simulation (DNS) studies on droplet growth in
turbulence, condensational growth and collisional growth were treated
separately. Studies in recent decades have postulated that small-scale
turbulence may accelerate droplet collisions when droplets are still small
when condensational growth is effective. This implies that both processes
should be considered simultaneously to unveil the full history of droplet
growth and rain formation. This paper introduces the first direct
numerical simulation approach to explicitly study the continuous droplet growth by condensation and collisions
inside an adiabatic ascending cloud parcel. Results from the
condensation-only, collision-only, and condensation–collision experiments are
compared to examine the contribution to the broadening of droplet size
distribution (DSD) by the individual process and by the combined processes.
Simulations of different turbulent intensities are conducted to investigate
the impact of turbulence on each process and on the condensation-induced
collisions. The results show that the condensational process promotes the
collisions in a turbulent environment and reduces the collisions when in
still air, indicating a positive impact of condensation on turbulent
collisions. This work suggests the necessity of including both processes
simultaneously when studying droplet–turbulence interaction to quantify the
turbulence effect on the evolution of cloud droplet spectrum and rain
formation