The compressible evolution of the super-Alfvénic magnetized wake

Abstract

The effects of compressibility on the linear and nonlinear properties of the magnetized wake are examined, with an emphasis on the high speed flow situation. It is found that compressibility can modify properties of this system previously identified for the incompressible case. Of particular interest is an investigation of how the properties of the magnetized wake vary with the sonic Mach number. It is found that, in general, the growth rates of the unstable sinuous and varicose modes decrease with increasing Mach number and with increasing Alfvén number. However, at high sonic Mach numbers the varicose modes can have a growth rate which increases as the spanwise wave number increases, a significant difference from the incompressible case. The linear compressible equations are solved by a Chebyshev collocation technique. Nonlinear computations based on a finite volume method are also presented. Growth rates computed by both codes in the linear regime are in excellent agreement. At long times the system relaminarizes to an overall accelerated and broadened wake channel. It is found that variations in the Mach and Alfvén numbers have a strong affect on the evolution of the magnetized wake, e.g., for high M fast magnetosonic shocks are observed to develop.