[FLASH-USERS] 2D Spherical and Cartesian Geometry

[Klaus Weide]

On Fri, 23 Sep 2016, Mordecai-Mark Mac Low wrote:

> Dear Michiel,
> 
> On your second question: are you sure that you’re not setting up a 
> cylindrical blast wave, rather than a spherical one?  A 2D, slab 
> symmetric, point explosion is effectively that of an infinite line 
> charge, rather than a spherical, point explosion.  The line charge 
> indeed expands faster.  There is, of course, an exact analytic solution 
> for this. For an analogous case with a constant energy input, see eqs. 
> 5-7 of Mac Low, McCray, & Norman, ApJ (1989). Therefore, you may be fine 
> sticking with your Cartesian grid, so perhaps you don’t need to solve 
> your first problem.

Yes indeed, to the above.

There is also a subsection in the FLASH Users Guide with some discussion 
related to the meaning of 2D simulations, which might be useful to some:

  8.11 Grid Geometry
  8.11.1 Understanding Curvilinear Coordinates


Michiel, you may also want to refer to the provided SodSpherical example.
1) Note that Y ranges only from 0 to 90 degrees, with reflecting 
boundaries in Y direction.
2) Note that the *physical* geometry set up in the SodSpherical problem
is cylindrical - comparable to a line charge - but the coordinates used by 
FLASH are spherical, thus in the parfile:

  # Grid geometry
  geometry = "spherical"



Klaus