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:

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. You can use the above 3D plot for orientation. 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
movie​	movie​	movie​

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

Was not obvious which field orientation would be best to use for the transverse (i.e. perpendicular to the flow direction) field run, since the shear angle breaks the symmetry of the cylinder. So to compare the difference, here are 3D low runs of the Shear 15, Beta=1 case.

Beta = 1

In column density, the transverse runs (y-field and z-field) are mirror images of each other. This can be seen at once looking down the barrel in x. When looking transversely, orient yourself to the direction of the incoming flow along x, then consider the direction of the field using the coordinate axes at bottom of each column. You will see that the same behavior is seen between the different orientations. That is, the middle box has same behavior as bottom right box, when you consider the relative directions of the field and the colliding flows.

And here are the 3 different initial conditions for orientation:

Bx

By

Bz

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