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Astrophysical Plasmas Group

Numerical Simulations


Problems, Methods, and Computers

Our group performs numerical simulations of fluid dynamics and magnetofluid dynamics. Most of the codes have been developed by members of our group and are written in Fortran or C based on pseudospectral methods. However, we also have codes based on finite differences and finite elements. Codes were developed in two and three dimensions, with different purposes involving research and education. Some of the applications are
Simulations are carried on different computers, ranging from desktop computers to massive parallel systems. Some of the simulations were carried on an Sgi Origin 2000 parallel computer (UBA - Physics Dept.). The group is also testing a beowulf cluster of 40 nodes (UBA - Physics Dept.).


Hydrodynamic simulations

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A 2D hydrodynamic code (with an MHD counterpart) was developed in our group for teaching and educational purposes. The code is written in Fortran 77 and a graphic user interface prepared for Linux is also available. The code is based on a pseudospectral scheme and solves the Navier-Stokes equations in a square box with periodic boundary conditions. This code is freely available (please contact mininni@df.uba.ar) and was used by members of our group to teach several courses on turbulence and fluid dynamic.
The image shows the simulation of a submerged jet using our 2D hydrodynamic code (click the image to see an animation).
 2D hydrodynamic jet

Click on the image to see an animation

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Jet/cloud colission The group also has hydrodynamic codes in three dimensions, which are used for modelling of isotropic turbulence and astrophysical applications.
The image shows constant density surfaces in a 3D simulation of the collision of a jet with a dense molecular cloud. The simulation was performed with an adaptive mesh grid of 1024x1024x1024 points (click on the image to see a movie).



Magnetohydrodynamic (MHD) and Hall-MHD simulations

Magnetohydrodynamic codes were developed in two and three dimensions by members of our group to study magnetic reconnection, dynamo mechanisms, turbulent coronal heating, and different astrophysical problems.
Most of these codes are pseudospectral with periodic boundary conditions. Depending on the code, time derivatives are computed using either Runge-Kutta methods, predictor-corrector methods, and also an implementation of a leap-frog method. The group also have developed codes in the reduced MHD approximation (RMHD). These codes use a combination of pseudospectral methods and finite differences to compute time derivatives.

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Hall-MHD simulation
We also have a three dimensional code to solve the MHD system in presence of Hall currents (Hall-MHD). This is also a pseudospectral code, mainly intended to study the impact of the Hall effect in turbulent dynamo mechanisms and in magnetic reconnection. The figure shows magnetic field intensity in a cubic box with periodic boundary conditions (click on the image to see a movie).
Click on the image to see an animation


More simulations

Shallow water
We also have developed codes to solve the hydrodynamic and magnetohydrodynamic equations in special approximations or geometries  whichare of interest in some astrophysical environments. Some examples are: codes to numerically solve the kinetic dynamo equations , the Burger's equation, and the HD and MHD equations in the shallow water approximation.
The figure shows current and magnetic field (arrows) for an MHD shallow water simulation in a square box with periodic boundary conditions, using a pseudospectral method to compute spatial derivatives and Runge-Kutta of order 2 to compute time derivatives.
Slice of current, and magnetic field (arrows)