wiki:u/erica/AccretionModelingBlog

Version 10 (modified by Erica Kaminski, 7 years ago) ( diff )

Bondi Accretion

3/18/2018

Am working on a 3D simulation of Bondi Flow onto a central sink particle and studying the accretion properties using the Krumholz accretion algorithm.

The setup has the following parameters (in computational units):

Lx=Ly=Lz 20
MaxLevel (AMR) 2
Mx=My=Mz 64
Effective resolution (dx) .15625
Sink dx = 4dx .625

From Bondi (1952) we have the following quantities (in order: Bondi radius, accretion rate, sonic radius, nondimensional density and velocity):

In the above, is a numerical coefficient which controls the strength of the accretion flow. At its critical value, , is strongest. In the code, is solved for using Eqn. 18 in Bondi's paper. In this simulation, these parameters are:

.2526
1.66

Additionally, we have:

1.291
~1
~1
.14318E+13
25.63
.0128
2692.17

The case of flow is an extreme limit for the solution space. This value of has a few interesting features:

Results

The simulation setup reproduces the correct nondimensional profiles. Here's a comparison of the t=0 nondimensional density and velocity profiles astrobear calculates for the bondi module (left), compared to the Bondi solutions for (curves II and III for the case of ).

However, the accretion rate onto the particle does not match the theoretical value. Sampling the mass of the particle over 10 different times shows the accretion rate to be fairly constant at,

(note, the sim was ran for about the freefall time of the average density in the box)

Mesh

Library

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