The closure of a turbulence field is a longstanding fundamental problem, while most closure models are introduced in spectral space. Inspired by Chou＇s quasi-normal closure method in spectral space, we propose an ana...The closure of a turbulence field is a longstanding fundamental problem, while most closure models are introduced in spectral space. Inspired by Chou＇s quasi-normal closure method in spectral space, we propose an analytical closure model for isotropic turbulence based on the extended scale similarity theory of the velocity structure function in physical space. The assumptions and certain approximations are justified with direct numerical simulation. The asymptotic scaling properties are reproduced by this new closure method, in comparison to the classical Batchelor model.展开更多
We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory.By introducing a fractal approach to describe the chaotic dynamical behavio...We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory.By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization,we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons,and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy.We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons.Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field,and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms.It is shown that,besides the electric and magnetic fields,core scattering is a primary factor in the fractal dynamics.展开更多
Scale similarity is found in many natural phenomena in the universe,from fluid dynamics to astrophysics.In large eddy simulations of turbulent flows,some sub-grid scale(SGS)models are based on scale similarity.The ear...Scale similarity is found in many natural phenomena in the universe,from fluid dynamics to astrophysics.In large eddy simulations of turbulent flows,some sub-grid scale(SGS)models are based on scale similarity.The earliest scale similarity SGS model was developed by Bardina et al.,which produced SGS stresses with good correlation to the true stresses.In the present study,we perform a mathematical analysis of scale similarity.The analysis has revealed that the ratio of the resolved stress to the SGS stress is g2,where g is the ratio of the second filter width to the first filter width,under the assumption of small filter width.The implications of this analysis are discussed in the context of large eddy simulation.展开更多
文摘The closure of a turbulence field is a longstanding fundamental problem, while most closure models are introduced in spectral space. Inspired by Chou＇s quasi-normal closure method in spectral space, we propose an analytical closure model for isotropic turbulence based on the extended scale similarity theory of the velocity structure function in physical space. The assumptions and certain approximations are justified with direct numerical simulation. The asymptotic scaling properties are reproduced by this new closure method, in comparison to the classical Batchelor model.
基金Project supported by the Natural Science Foundation of Shandong Province,China(Grant No.ZR2014AM030)
文摘We study the ionization of helium Rydberg atoms in an electric field above the classical ionization threshold within the semiclassical theory.By introducing a fractal approach to describe the chaotic dynamical behavior of the ionization,we identify the fractal self-similarity structure of the escape time versus the distribution of the initial launch angles of electrons,and find that the self-similarity region shifts toward larger initial launch angles with a decrease in the scaled energy.We connect the fractal structure of the escape time plot to the escape dynamics of ionized electrons.Of particular note is that the fractal dimensions are sensitively controlled by the scaled energy and magnetic field,and exhibit excellent agreement with the chaotic extent of the ionization systems for both helium and hydrogen Rydberg atoms.It is shown that,besides the electric and magnetic fields,core scattering is a primary factor in the fractal dynamics.
基金The authors gratefully acknowledge the support by NASA under grant NNX12AK04A monitored by Dr.H.T.Huynh and AFOSR under grant FA95501210286 managed by Dr.Fariba Fahroo.
文摘Scale similarity is found in many natural phenomena in the universe,from fluid dynamics to astrophysics.In large eddy simulations of turbulent flows,some sub-grid scale(SGS)models are based on scale similarity.The earliest scale similarity SGS model was developed by Bardina et al.,which produced SGS stresses with good correlation to the true stresses.In the present study,we perform a mathematical analysis of scale similarity.The analysis has revealed that the ratio of the resolved stress to the SGS stress is g2,where g is the ratio of the second filter width to the first filter width,under the assumption of small filter width.The implications of this analysis are discussed in the context of large eddy simulation.
