Comparison of Lorenz type and plasma fluid models for nonlinear-interchange-mode generation of shear flow

By solving nonlinear fluid model equations, it is shown that the nonlinear interchange mode generates shear flow through Reynolds stress, which suppresses fluctuation amplitude substantially. The nonlinear interaction between vortex motion and shear flow produces a relaxation oscillation. This behaviour is also confirmed by a Lorenz type model with five ordinary differential equations. However, for the same Rayleigh number and Prandtl number (Pr=1.0), the period of relaxation oscillation becomes shorter and the amplitude of vortex motion becomes smaller. (author)