Kelvin- Helmholtz Instability
Introduction
The Kelvin- Helmholtz instability is created by two fluids moving past one another in opposite directions. Pressure and density are initially uniform throughout the grid. The top half of the grid will move to the right and the bottom half to the left. Small perturbations are added to seed the instability.
2d Tests
All 2d KH tests were run on a 600 x 600 grid with a physical size of -0.5 x 0.5 in both dimensions. Pressure was initialized to 0.6 throughout the grid and density at 1.0. The x component of the velocity was set throughout the grid as -0.5 U TANH ( 25.0 * y), where U = 1.0. Using this creates a transition region for the change in x velocity.
Results
Ma= Infinity ( No B field )
Below is a movie of color. Note the "cat's eye".
Ma = 1000 ( Weak B field) Bx = 1e-3
Below is a movie of color.
Below is a movie of the magnitude of the magnetic field.
Ma = 5 ( Strong B field ) Bx = 0.2
Below is a movie of color for the strong field case. Note that the instability is unable to persist in this case.
Below is a movie of the magnitude of the magnetic field during this same instability.
More Information
Frank A., Jones T. W., Ryu D. & Gaalaas J. B., 1996, Astrophysical Journal, 460, 777 (ADS Link)