Fundamental aspects of turbulence and turbulent mixing are investigated using direct numerical simulations (DNS) of stationary isotropic turbulence, with Taylor-scale Reynolds numbers ranging from 8 to 650 and Schmidt numbers from 1/8 to 1024. The primary emphasis is on important scaling issues that arise in the study of intermittency, mixing and turbulence under solid-body rotation.
Simulations up to 2048^3 in size have been performed using large resource allocations on Terascale computers
at leading supercomputing centers.
Substantial efforts in algorithmic development have also been undertaken
and resulted in
a new code based on a two-dimensional domain decomposition
which allows
the use of very large number of processors.Benchmark tests indicate
very good parallel performance
for resolutions up to 4096^3 on up to 32768 processors.
Investigation of intermittency through the statistics of
dissipation and enstrophy in a series
of simulations at the same Reynolds number but different
resolution indicate that accurate
results in high-order moments require a higher degree
of fine-scale resolution than commonly practiced.
At the highest Reynolds number in our simulations (400 and 650)
dissipation and enstrophy exhibit
extreme fluctuations of O(1000) the mean
which have not been studied in
the literature before and suggest a universal scaling
of small scales.
Simulations at Reynolds number of 650 on 2048^3 grids
with scalars at Sc=1/8 and 1
have allowed us to obtain the clearest evidence of attainment of
inertial-convective scaling in the scalar spectrum
in numerical simulations to date whereas
results at high Sc support k^{-1} viscous-convective scaling.
Intermittency for scalars as measured by the tail of the PDF of scalar dissipation
and moments of scalar gradient fluctuations is found to saturate at high Sc.
Persistent departures from isotropy are observed as the Reynolds number increases.
However, results suggest a return to isotropy
at high Schmidt numbers, a tendency that appears to be stronger
at high Reynolds numbers.
The effects of the Coriolis force on
turbulence under solid-body rotation are investigated using
simulations on enlarged solution domains which
reduce the effects of
periodic boundary conditions.
| Identifer | oai:union.ndltd.org:GATECH/oai:smartech.gatech.edu:1853/19794 |
| Date | 09 August 2007 |
| Creators | Donzis, Diego Aaron |
| Publisher | Georgia Institute of Technology |
| Source Sets | Georgia Tech Electronic Thesis and Dissertation Archive |
| Detected Language | English |
| Type | Dissertation |
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