Scaling of turbulence and turbulent mixing using Terascale numerical simulations

Turbulence;Fluid dynamics;Large scale simulations;Direct numerical simulations

Donzis, Diego Aaron ; Aerospace Engineering

University:Georgia Institute of Technology

Department:Aerospace Engineering

关键词: Turbulence;    Fluid dynamics;    Large scale simulations;    Direct numerical simulations;   

Others  :  https://smartech.gatech.edu/bitstream/1853/19794/1/donzis_diego_a_200712_phd.pdf

美国|英语

来源: SMARTech Repository

【 摘 要 】

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 computersat leading supercomputing centers.Substantial efforts in algorithmic development have also been undertakenand resulted ina new code based on a two-dimensional domain decompositionwhich allowsthe use of very large number of processors.Benchmark tests indicatevery good parallel performancefor resolutions up to 4096^3 on up to 32768 processors.Investigation of intermittency through the statistics ofdissipation and enstrophy in a seriesof simulations at the same Reynolds number but differentresolution indicate that accurateresults in high-order moments require a higher degreeof fine-scale resolution than commonly practiced.At the highest Reynolds number in our simulations (400 and 650)dissipation and enstrophy exhibitextreme fluctuations of O(1000) the meanwhich have not been studied inthe literature before and suggest a universal scalingof small scales.Simulations at Reynolds number of 650 on 2048^3 gridswith scalars at Sc=1/8 and 1have allowed us to obtain the clearest evidence of attainment ofinertial-convective scaling in the scalar spectrumin 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 dissipationand 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 isotropyat high Schmidt numbers, a tendency that appears to be strongerat high Reynolds numbers.The effects of the Coriolis force onturbulence under solid-body rotation are investigated usingsimulations on enlarged solution domains whichreduce the effects ofperiodic boundary conditions.