Version 56 (modified by 11 years ago) ( diff ) | ,
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3D MHD Shear Flows
Diameter | 40 pc |
Mach | 1.5 |
Shear Angles | 15, 30, 60 degrees |
Density | 1 cm-3 |
Beta | 1, 10 |
Initial B-field orientation | Uniform in x |
Cells/Jeans Length | 64 |
Cooling | II curve |
Final time | 20 Myr |
Resolution | 48 + 2 ~ 200 cells effective |
Box size | 62.5 x 75 x 75 pc in x,y,z |
Boundary conditions | Outflow-only, and multipole for gravity |
Self-gravity | On |
Orientation of Collision Interface
Plot showing the direction of the tilted interface:
The interface is tilted about y. This is the Shear 15 case.
Parallel-field case; Beta = 1,10
The field is initialized to be uniformly distributed throughout the cylinder and the ambient medium, oriented along the flow axis.
Evolution of the tilted interface
A slice taken through the center of the box, in the x-z plane, shows that in the strong magnetic field case, the interface tends to realign so that it is vertical:
For production runs, the domain needs to be extended in x so that the sheared interface doesn't reach the boundaries.
Instabilities: Beta = 1 is too strong of a field, as it completely prevents formation of the 3 instabilities relevant to molecular cloud formation; thermal instabilities, kelvin helmoltz waves, and the NTSI are all absent in the strong field case. The NTSI seems to be strongest in the hydro case, and KH seems to increase in strength with increasing shear angle.
Column Density Maps
These column density maps are made by summing the density over all cells through a given dimension, using both the gas and sink components of mass/cell. Recall, the interface is rotated about y (as can be seen in above plot). In the 'down the barrel case', the vertical dimension is z, and the horizontal axis is y. The axes are given in the other plots.
'Down the Barrel'
Down Y
Down Z
A strong ring effect is present in the strong beta cases that isn't in the weaker B field and hydro case.
Peak Densities and Sink Particles
A strong magnetic field leads to more sink particles forming by the end of the simulation compared to the hydro case, but at slightly later times.
A weak field case tends to just delay the formation of sinks, but doesn't seem to enhance the number of sinks that form.
This trend holds for both the Shear 15 and Shear 30 cases.
In contrast, the Shear 60 cases do not make sinks, except for the weak field case that makes 1 by the end of the sim.
Run | Time when sink first appears | Number of sinks by end |
Beta1, Shear15 | Frame 160/200, t=16 Myr | 8 |
Beta1, Shear30 | Frame 173/200, t=17 Myr | 7 |
Beta1, Shear60 | No Sinks Form | 0 |
Beta10, Shear15 | Frame 184/200, t=18 Myr | 5 |
Beta10, Shear30 | Frame 161/200, t=16 Myr | 2 |
Beta10, Shear60 | Frame 196/200, t=19.5 Myr | 1 |
Hydro, Shear15 | Frame 118/200, t=11 Myr | 6 |
Hydro, Shear30 | Frame 146/200, t= 14.5 Myr | 3 |
Hydro, Shear60 | No Sinks Form | 0 |
Here is a plot of the peak densities in the grid over time:
Perpendicular-field cases
It was not obvious which field orientation to use for the perpendicular field cases, since the shear angle breaks the symmetry of the cylinder. So to compare the difference, here are 3D low res runs of the Shear 15 case with either a y or z field. These were run with Beta = 1 and Beta = 10.
Beta = 1, y-field
Beta = 10, y-field
Beta = 1, z-field
Beta = 10, z-field
Peak densities and sink particles
Further, peak densities were similar in the transverse cases and both did not form sinks,
B-field Direction | Peak Density at .25, .50, .75, 1 | Time first sink formed | No. of sinks by end |
x | 229, 947, 2383, 4934 | 15 Myr | 8 |
y | 27, 58, 69, 88 | -No sinks form- | 0 |
z | 22, 51, 50, 58 | -No sinks form- | 0 |
Beta = 10
B-field Direction | Peak Density at .25, .50, .75, 1 | Time first sink formed | No. of sinks by end |
x | 598, 1140, 1535, 1487 | 18 Myr | 5 |
y | 83, 210, 255, 225 | -No sinks form- | 0 |
z | 58, 132, 194, 163 | -No sinks form- | 0 |
Issues with the perpendicular case
Attachments (40)
- ColDensX_CF15_Beta1.gif (11.0 MB ) - added by 11 years ago.
- ColDensX_CF15_Beta10079.png (37.8 KB ) - added by 11 years ago.
- ColDensY_CF15_Beta10079.png (29.7 KB ) - added by 11 years ago.
- ColDensY_CF15_Beta1.gif (7.3 MB ) - added by 11 years ago.
- ColDensZ_CF150079.png (32.2 KB ) - added by 11 years ago.
- ColDensZ_CF15_Beta1.gif (8.4 MB ) - added by 11 years ago.
- down_x0114.png (145.9 KB ) - added by 11 years ago.
- down_x_coldens.gif (16.3 MB ) - added by 11 years ago.
- down_y0114.png (87.5 KB ) - added by 11 years ago.
- down_y_coldens.gif (13.5 MB ) - added by 11 years ago.
- down_z0114.png (116.9 KB ) - added by 11 years ago.
- down_z_coldens.gif (17.4 MB ) - added by 11 years ago.
- shear30axes.png (32.4 KB ) - added by 11 years ago.
- shear15axes.png (29.9 KB ) - added by 11 years ago.
- shear60axes.png (38.1 KB ) - added by 11 years ago.
- xz_plane_rho0029.png (62.1 KB ) - added by 11 years ago.
- xz_plane_rho.gif (9.7 MB ) - added by 11 years ago.
- Hydro.png (37.0 KB ) - added by 11 years ago.
- Beta10.png (36.7 KB ) - added by 11 years ago.
- Beta1.png (35.7 KB ) - added by 11 years ago.
- Bx_Init.png (39.9 KB ) - added by 11 years ago.
- Bz_Init.png (42.1 KB ) - added by 11 years ago.
- By_Init.png (46.1 KB ) - added by 11 years ago.
- diff_fields_compare.gif (21.1 MB ) - added by 11 years ago.
- b1s15ycdm.2.gif (16.6 MB ) - added by 11 years ago.
- b10s15zcdm.gif (19.2 MB ) - added by 11 years ago.
- b1s15zcdm.gif (12.8 MB ) - added by 11 years ago.
- b10s15ycdm.gif (18.2 MB ) - added by 11 years ago.
- b1s15ycdm.gif (16.6 MB ) - added by 11 years ago.
- b10s15xcdm.gif (31.1 MB ) - added by 11 years ago.
- b1s15xcdm.gif (22.1 MB ) - added by 11 years ago.
- HydroS60_nosinks.gif (21.2 MB ) - added by 11 years ago.
- B1S15CDM_sinks.gif (12.1 MB ) - added by 11 years ago.
- B10S30CDM_sinks.gif (18.8 MB ) - added by 11 years ago.
- B10S60CDM_sinks.gif (17.5 MB ) - added by 11 years ago.
- B10S15CDM_sinks.gif (17.9 MB ) - added by 11 years ago.
- B1S60CDM_nosinks.gif (14.2 MB ) - added by 11 years ago.
- B1S30CDM_sinks.gif (13.5 MB ) - added by 11 years ago.
- HydroS30_sinks.gif (21.5 MB ) - added by 11 years ago.
- HydroS15CDM_sinks.gif (20.0 MB ) - added by 11 years ago.