Update 3/26: Wind Tunnel Run 007

Finished Runs

WT Run 007

Same setup with Run006B: softening length resolved by 16 pixels. Region of highest refinement et to 30 CUs. Box size is set to be 20483 CUs, 23 as large as those of Run 006s, 43 as large as Run 005s. This enables a increase of run time to 2CU.

Log density & velocity vectors movie:

As shown in the movie, although the density disturbance around the particle is almost always contained within the box, near the end of the simulation gas velocities at the boundaries are altered due to gas self-gravity. In other words the gas across the box begins to collapse onto itself. This is to be expected since the box is larger than the Jeans scale of the gas, and self-gravity introduces positive feedback to "accretion" around the point particle.

The dynamic friction also confirms this positive feedback. In the shorter timescale used before (¼ of total runtime), Run 007 does not stand out -

But the drag blows up later -

Which can be fitted by an exponential function - F = f0*Exp(t/tau) + c

Here f0 = 0.157, tau = 7.442, and c = 2.324.

Constant offset c here can represent the drag force as predicted by BHL, ignoring self-gravity.

To avoid using incorrect DF measurements due to limited box size, I am running currently Run 007B, which is the same setup as Run 007 but with a factor of 23 box.

Next Steps - parameter space? Non-dimensionalization?

I think the simulation module has become mature enough that exploring a larger portion of the parameter space becomes possible. MacLeod suggested me to non-dimensionalize the problem, to better aim at the physics. I am studying his (their) approach - there might be some difficulties in, for instance, the scalability of density. But even in cgs we can still artificially alter Mach number, density and the particle mass, etc.

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