Dynamical aspect of entropy transfer in free convection turbulence

摘要

From a dynamical perspective, entropy transfer processes are investigated in two-dimensional free convection turbulence in comparison with an entropy cascade picture based on the coupled dynamics of the T vorticity chi=(partial derivative(y)T,-partial derivative(x)T) and the velocity gradient tensor. Typical entropy transfer processes are observed in direct numerical simulations. For these processes, two characteristic times, the transfer time and the staying time are determined: the farmer time obeys a Bolgiano-Obukhov (BO) time scaling corresponding to the eddy turnover time in energy cascade. It is suggested that this typical transfer process is not an elementary process of cascade but a dynamical manifestation of intermittency. To examine the meaning of the characteristic times of the typical entropy transfer process, a shell model is constructed based on the entropy cascade picture. By this model, it is shown numerically that typical entropy transfer processes are regarded as the fluctuations satisfying a dynamical similarity. This similarity proved by perturbation analysis requires naturally that the transfer time should obey the BO time scaling. [References: 24]