Changes between Version 14 and Version 15 of u/erica/OutflowFeedback


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Timestamp:
10/17/17 18:25:05 (7 years ago)
Author:
Erica Kaminski
Comment:

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  • u/erica/OutflowFeedback

    v14 v15  
    33The outflow module injects a fraction of accreted mass, momentum and angular momentum back into the grid following each accretion time step and between hydro advances.
    44
    5 Before we discuss the details of this routine, let us briefly recall the accretion prescription here. The feedback module is currently configured to work with the Bondi accretion routine in the code (aka Krumholz accretion). This routine establishes a mass cut-off of gravitationally unstable material around the sink particle (in a control volume of radius = 4dx). Any mass greater than this cut off is removed from the ith cell in this volume and placed into the sink particle:
     5== Brief Accretion Module Review ==
    66
    7 This implies that the momentum in the ith cell has now decreased discontinuously over the accretion step. To correct for this, the `missing' momentum is placed into the sink particle:
     7Before we discuss the details of this routine, let us briefly recall the accretion prescription here. The feedback module is currently configured to work with the Bondi accretion routine in the code (aka Krumholz accretion). This routine establishes a mass cut-off of gravitationally unstable material around the sink particle (in a control volume of radius = 4dx). Any mass greater than this cut off is removed from the ith cell in this volume (i.e. ''is accreted'') and placed into the sink particle. The ''total'' accreted mass is then given by:
     8
     9$M_{acc} = \Sigma (m_{i}-m_{i, thresh})$
     10
     11Simply removing this mass from the cells contained within the kernel leads to an overall decrease in the momenta in the grid over the accretion step. To correct for this, the `missing' momentum is placed into the sink particle, i.e. momentum is conserved between the grid (gas) and the sink particle. For example, the components of the accreted momentum vector is:
     12
     13$p_{x, acc} = \Sigma p_{x,i} = M_{acc}\Sigma v_{x,i}$
     14
     15$p_{y, acc} = \Sigma p_{y,i} = M_{acc}\Sigma v_{y,i}$
     16
     17$p_{z, acc} = \Sigma p_{z,i} = M_{acc}\Sigma v_{z,i}$
     18
     19
     20The same is so with Energy:
     21
     22Now, jets are launched from rotating protostellar systems, so it makes sense to assign a 'spin' to the sink particle, induced from accreting angular momentum from the surrounding gas. While we do not explicitly conserve angular momentum in the code, angular momentum would be reduced in the grid due to the accretion step, and so to be conservative between the gas and sink particle, we assign a total accreted angular momentum to the sink as follows:
     23
     24Note, this accreted ngular momentum is the sink's ''spin'' angular momentum, rather than its orbital angular momentum. This is because in addition to enforcing mass, momentum, and energy conservation between the gas and the sink particle, we also conserve the COM of the system.
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