Evrard Collapse Problem

This is a standrard SPH test problem. A 1/r density sphere of cold gas is allowed to collapse under it's own grvaity in an isolated box. The setup for this problem is called evrard (MNRAS 235 (1988) 911). This problem was setup by Colin McNally (Colin's evrard page).

To get into the FLASH code and the physics of self gravitational collapse, I tried to reproduce Colin's results using his setup.

The resolution study (see below) shows that the energy conservation improves significantly (is less worse) by increasing the maximal refinement levels from 5 to 6/7 (unfortunately, the 'r_max = 7' run did not finish due to unkown problems with idra and/or flash).

Initial radial density distribution (r_max = 6).

Initial radial pressure distribution (r_max = 6).

Radial density distribution at about 0.8 free fall time.

Radial pressure distribution at about 0.8 free fall time.

Some statements

• Although, effects due to moderate grid resolutions are quite visible (see pictures below) the qualitative Flash-solutions match that of Evrard.
• All simulations used the 'multigrid' gravity solver. The multipole solver didn't work for FLASH2.1 (this solver supposed to be particular appropriate for spherical problems).

2D slices of density and pressure at the center of the simulation box using XFLASH IDL routines. Also the refined blocks are shown.

Some nice 3D pictures from the of density, pressure and x-velocity using SLICER3 IDL-function. The pictures are compiled from the 'r_max=6' run at about t = 0.8 free fall time.