CFD-MHD Project Research Highlights

Zeus 2D Simulations of Wide-angle winds

Hsien Shang, together with research assistant Mei-Yin Chou and Anthony Allen are carrying out studies of MHD flows by Zeus2D. Simulations of wide-angle winds are done on their asymptotic regime and for long-term evolution to achieve time-steady state, and to further investigate the implications on the formation of outflows by interacting these wide-angle winds with ambient media. They adopted analytic construction for the MHD wind where the density, poloidal and toroidal velocity, and toroidal magnetic fields follow a simple power-law relationship from Li & Shu (1996). Due to the sharp drop-off in density and magnetic field strengths characterized by such winds, and large spatial coverage in the computational domains, establishing robust numerical results has been a challenging task. The numerical boundary and reflection effects arise very easily. To establish robust runs and performances based on local resources, they first established benchmark tests on various platforms of locally accessible ASIAA machines and with the use of a variety of optimization flags, the benchmark is summarized in Allen, Chou, and Shang (2002). Steady-state runs have also been established for super-Alfv\'enic winds running into vacuum from a narrow launch sphere of hidden zones in the hope to mimic the x-winds.

On the effects of wide-angle winds interacting with ambient environment, in progress are the simulations of winds running into surrounding medium of constant density, and later on more realistic configurations from Li and Shu (1997) toroid model sequences may be implemented. In the figures are simulations of winds of terminal speed of 300 km/s (~ 3 Va) and ambient densities from 10-16 and 10-19g/cm3. These results are plotted on four-panels to illustrate selected time frames of 100, 400, 700, and 1000 years of evolution. The appearance of the resultant density structures and shapes of shock fronts suggests strong connections to the lobe shapes of molecular outflows. Further work will continue to investigate such connections.