Boundary Effects

Boundary noise can manifest when subsonic waves near the boundary cause errors that may propagate inward with speed less or equal to the sound speed. Thus to consider if such a disturbance has time enough to travel from the boundary to the BE sphere/ambient boundary, I put together this table that shows the sound speed of the ambient, the final time of the simulation, and the distance that a sonic wave would travel in this time. For all cases, except for the stability case, sonic disturbances from the boundary do not have time enough to propagate from the boundary to the sphere's surface. Note, I have taken the boundary to be the sphere of radius = 15, centered on the origin.

Case	Sound Speed Ambient	Tsim	Distance sound wave from boundary can travel	Does flow at boundary become supersonic?
Matched	4.491	0.216	0.97 RBe ~ 1/15 Domain	yes
BP	42.82	0.192	8.2 RBe ~ ½ Domain	no
Stability	44.91	1.1	44 RBe ~ 3*Domain	no
1/3 Ambient	8	0.28	2.25 RBe	yes
1/10 Ambient	4.491	0.216	0.97 RBe	yes
1/30 Ambient	4.491	0.216	0.97 RBe	yes

Below are 2D slices of pseudocolor plots showing rho and vrad/cs.

Matched

BP

Ambient 1/3

Ambient 1/10

Ambient 1/30